Apley's Orthopedics chapter 20- the knee

Blount's disease This is a progressive bow-leg deformity associated with abnormal growth of the posteromedial part of the proximal tibia. The children are usually overweight and start walking early; the condition is

bilateral in 80 per cent of cases. Children of negroid descent appear to be affected more frequently than others. Deformity is noticeably worse than in physiological bow legs and may include internal rotation of the tibia. The child walks with an outward thrust of the knee; in the worst cases there may be lateral subluxation of the tibia.

OSTEOCHONDRITIS DISSECANS The prevalence of osteochondritis dissecans is between 15 and 30 per 100 000 with males being affected more often than females (ratio 5:3). An increase in its incidence has been observed in recent years, probably due to the growing participation of young children of both genders in competitive sports. A small, well-demarcated, avascular fragment of

bone and overlying cartilage sometimes separates from one of the femoral condyles and appears as a loose body in the joint. The most likely cause is trauma, either a single impact with the edge of the patella or repeated microtrauma from contact with an adjacent tibial ridge. The fact that over 80 per cent of lesions occur on the lateral part of the medial femoral condyle, exactly where the patella makes contact in full flexion, supports the first of these. There may also be some general predisposing factor, because several joints can be affected, or several members of one family. Lesions are bilateral in 25 per cent of cases

diagnosis. Investigations should include Mantoux testing and synovial biopsy. The ideal is to start antituberculous chemotherapy before joint destruction occurs. SWELLINGS IN FRONT OF THE JOINT PREPATELLAR BURSITIS ('HOUSEMAID'S KNEE') The fluctuant swelling is confined to the front of the patella and the joint itself is normal. This is an uninfected bursitis due not to pressure but to constant friction between skin and bone. It is seen mainly in carpet layers, paving workers, floor cleaners and miners who do not use protective knee pads. Treatment consists of firm bandaging, and kneeling is avoided; occasionally aspiration is needed. In chronic cases the lump is best excised.

lump is best excised. Infection (possibly due to foreign body implantation) results in a warm, tender swelling. Treatment is by rest, antibiotics and, if necessary, aspiration or excision. INFRAPATELLAR BURSITIS ('CLERGYMAN'S KNEE') The swelling is below the patella and superficial to the patellar ligament, being more distally placed than prepatellar bursitis; it used to be said that one who prays kneels more uprightly than one who scrubs! Treatment is similar to that for prepatellar bursitis. Occasionally the bursa is affected in gout. OTHER BURSAE Occasionally a bursa deep to the patellar tendon or the pes anserinus becomes inflamed and painful. Treatment is non-operative.

TECHNIQUE For sound biomechanical reasons, a varus deformity is best corrected by a valgus osteotomy at the proximal end of the tibia, whereas a valgus deformity should be corrected by a varus osteotomy at the femoral supracondylar level. Angles must be accurately measured and the position of correction carefully mapped out on x-rays before starting the operation. A high tibial valgus osteotomy can be performed either by removing a pre-determined wedge of bone based laterally and then closing the gap (closing wedge technique) or by opening a wedge-shaped gap on the medial side (opening wedge technique).

medial side (opening wedge technique). In the lateral closing wedge method the fibula must first be released either by dividing it lower down or by disrupting the proximal tibio-fibular joint. The tibia is divided just above the insertion of the patellar ligament. Two transverse cuts are made, one parallel to the joint surface and another just below that, angled to create the desired laterally based wedge. The wedge of bone is removed and the fragments are then approximated and fixed in the corrected position either with staples or with compression pins. The limb is immobilized in a cast for 4-6 weeks, by which time the osteotomy should have started to unite.

RESULTS High tibial valgus osteotomy, when done for osteoarthritis, gives good results provided (1) the disease is confined to the medial compartment, and (2) the knee has a good range of movement and is stable. Relief of pain is good in 85 per cent of cases in the first year but drops to approximately 60 per cent after 5 years. A recent review has shown that modern medial

opening wedge osteotomy techniques can achieve sat- 20 isfactory postoperative alignment in 93 per cent of patients and survivorship rates of 94 per cent at 5- year, 85 per cent at 10-year, and 68 per cent at 15- year follow-up, with conversion to total knee arthroplasty as the end point (Brower et al., 2007; Virolainen and Aro, 2004). The clinical results of distal femoral varus osteotomy have been good in selected patients. Substantial improvements in pain and function can be expected in approximately 90 per cent of patients (Preston et al., 2005).

OSTEOTOMY Osteotomy above or below the joint used to be a popular method of treating arthritis of the knee, especially when articular destruction was more or less limited to one compartment and the knee had developed a varus or valgus deformity. With the development of joint replacement techniques, the operation gradually fell into disuse, or at best was seen as a temporizing measure to buy time for patients who would ultimately undergo some form of arthroplasty. However, improvements in technique and the introduction of

operations for meniscal and articular cartilage repair have led to renewed interest in this procedure. The rationale for osteotomy is based on both biomechanical and physiological principles. Malalignment of the limb results in excessive loading and stress in part of the joint and consequently increased damage to the articular cartilage in that area - the medial compartment if the knee is in varus and the lateral compartment in a valgus knee. As the articular surface is destroyed, the deformity progressively increases. Osteotomy and repositioning of the bone fragments, by correcting the deformity, will improve the loadbearing mechanics of the joint. Furthermore, it will reduce the intraosseous venous congestion, and this may relieve some of the patient's pain.

Treatment For the purposes of management, it is useful to 'stage' the lesion; hence the importance of radionuclide scanning, MRI and arthroscopy. Lesions in adults have a greater propensity to instability whereas juvenile osteochondritis is typically stable. Those lesions with an intact articular surface have the greatest potential

to heal with non-operative treatment if repetitive impact loading is avoided. In the earliest stage, when the cartilage is intact and the lesion is 'stable', no treatment is needed but activities are curtailed for 6-12 months. Small lesions often heal spontaneously

CLINICAL ASSESSMENT SYMPTOMS Pain, either insidious in onset or more acute, is the most common knee symptom. With inflammatory or degenerative disorders it is usually diffuse, but with mechanical disorders (and especially after injury) it is often localized - the patient can, and should, point to the painful spot. If the patient can describe the mechanism of the injury, this is extremely useful: a direct blow to the front of the knee may damage the patello-femoral joint; a blow to the side may rupture the collateral ligament; twisting injuries are more likely to cause a torn meniscus or a cruciate ligament rupture. Swelling may be diffuse or localized. If there was an injury, it is important to ask whether the swelling appeared immediately (suggesting a haemarthrosis) or only after some hours (typical of a torn meniscus). A complaint of recurrent swelling, with more or less normal periods in between, suggests a longstanding internal derangement - possibly an old meniscal tear, degeneration of the meniscus, a small osteoarticular fracture or loose bodies in the joint. Chronic swelling is typical of synovitis or arthritis.

typical of synovitis or arthritis. A small, localized swelling on the anteromedial or anterolateral side of the joint makes one think of a cyst of the meniscus (always on the medial side) or a floating loose body. Swelling over the front of the knee could be due to a prepatellar bursitis; a localized bulge in the popliteal fossa can also be caused by a bursal swelling, but is more often due to ballooning of the synovial membrane and capsule at the back of the joint. 'Stiffness' is a common complaint, but it must be distinguished from inhibition of movement due to pain, or simple weakness of the extensor apparatus. Particularly characteristic is stiffness that appears regularly after periods of rest - so-called 'post-inactivity stiffness' - which suggests some type of chronic arthritis.

SIGNS WITH THE PATIENT SITTING With the patient sitting sideways on the examination couch, the outlines of the patellae and patellar ligaments, as well as the general shape and symmetry of the two knees and the tibial tubercles, can be made out quite easily. With the knees dangling at 90 degrees of flexion, the patellae should be facing straight forwards; note if they appear to be seated higher than usual (patella alta) or lower than usual (patella baja). Patella alta is believed to be associated with a higher than normal incidence of chondromalacia patellae. Next, ask the patient to straighten each knee in turn and observe how the patella moves upwards. Does it

veer off towards one side in the early phase of knee extension and then slide back to the centre with full extension - suggesting a tendency to subluxation? Patellar alignment can also be assessed by measuring the Q-angle (quadriceps angle). This is the angle subtended by a line drawn from the anterior superior iliac spine to the centre of the patella and another from the centre of the patella to the tibial tubercle (Fig. 20.2c); it normally averages about 14 degrees in men and 17 degrees in women. An increased Q-angle is regarded as a predisposing factor in the development of chondromalacia; however, small variations from the norm are not a reliable indicator of future pathology.

HAEMOPHILIC ARTHRITIS The knee is the joint most commonly involved in bleeding disorders. Repeated haemorrhage leads to chronic synovitis and articular cartilage erosion. Movement is progressively restricted and the joint may end up deformed and stiff. Clinical features Fresh bleeds cause pain and swelling of the knee, with the typical clinical signs of a haemarthrosis (see Chapter 5). Between episodes of bleeding the knee often

continues to be painful and somewhat swollen, with restricted mobility. There is a tendency to hold the knee in flexion and this may become a fixed deformity. X-rays Radiographic examination may show little abnormality, apart from local osteoporosis. In more advanced cases the joint space is narrowed and large 'cysts' or erosions may appear in the subchondral bone.

SIGNS WITH THE PATIENT UPRIGHT For the examination, both lower limbs must be exposed from groin to toe; a mere hitching up of the skirt or rolling back of a trouser leg is not good enough. Deformity (valgus or varus or hyperextension) is best seen with the patient standing and bearing weight, lower limbs together (if possible!) and feet pointing forward. Normally the knees and ankles can touch in the midline; this means that the knees must be in slight valgus (about 7 degrees in women and

5 degrees in men), because the hips are wider than the knees. Genu valgum and genu varum are determined in relation to this normal anatomical alignment. But look carefully to see whether the deformity is really in the knee (often a sign of arthritis) and not in the lower end of the femur (a bone tumour?) or the upper end of the tibia (e.g. a malunited fracture, or maybe Paget's disease (see Fig. 20.1e)). Alignment of the extensor mechanism (quadriceps, patella and patellar ligament) can also be measured with the patient standing but is probably more conveniently done with the patient seated (see below). Gait is important; the patient should also be observed walking with and without any support such as a stick or crutch. In the stance phase note whether the knee extends fully (is there a fixed flexion deformity or a hyperextension deformity?) and see if there is any lateral or medial thrust signifying instability. In the swing phase note whether the knee moves freely or is held in one position - usually because the joint is painful but perhaps because it really is ankylosed! When the patient walks, is there any sign of a limp? And if so, does it stem from the knee? Or perhaps the hip, or the foot?

COMPLICATIONS Compartment syndrome in the leg This is the most important early complication of tibial osteotomy. Careful and repeated checks should be carried out during the early postoperative period to ensure that there are no symptoms or signs of impending ischaemia. Early features of compartment compression in the leg are sometimes mistaken for those of a deep vein thrombosis; this mistake should be avoided at all costs because the consequent delay in starting treatment could make the difference between complete recovery and permanent loss of function. Peroneal nerve palsy Overzealous attempts at correcting a longstanding valgus deformity can stretch and damage the peroneal nerve. Poor cast techniques may do the same, which is a good reason why postoperative cast application should not be left to an unsupervised junior assistant. Failure to correct the deformity Under- or overcorrection of the deformity are really failures in technique. With medial compartment osteoarthritis, unless a slight valgus position is obtained, the result is liable to be unsatisfactory. However, marked overcorrection is not only mechanically unsound but the cosmetic defect is liable to be bitterly resented by the patient. Delayed union and non-union These complications can be avoided by ensuring that fixation of the bone fragments is stable and secure.

ARTHRODESIS Arthrodesis of the knee has long been considered a demanding procedure that is subject to a variety of postoperative complications and often results in marginal or unacceptable outcomes. A stiff knee is a considerable disability; it makes climbing difficult and sitting in crowded areas distinctly awkward. Consequently, it is not often performed. For these reasons, arthrodesis has typically been held in reserve as a final salvage procedure for patients with irretrievably failed total knee arthroplasties and other comparable conditions. INDICATIONS In the past - and even today in some parts of the world - the main indications for arthrodesis of the knee were (and are) irremediable instability due to the late effects of poliomyelitis and painful loss of mobility due to tuberculosis or chronic pyogenic infection. In countries with advanced medical facilities the commonest indication is failed total knee replacement (either septic or aseptic).

The swelling may diminish following aspiration and injection of hydrocortisone; excision is not advised, because recurrence is common unless the underlying condition is treated. POPLITEAL ANEURYSM This is the commonest limb aneurysm and is sometimes bilateral. Pain and stiffness of the knee may precede the symptoms of peripheral arterial disease, so it is essential to examine any lump behind the knee for pulsation. A thrombosed popliteal aneurysm does not pulsate, but it feels almost solid.

BONY SWELLINGS AROUND THE KNEE Because the knee is a relatively superficial joint, bony swellings of the distal femur and proximal tibia are often visible and almost always palpable. Common examples are cartilage-capped exostoses (osteochondromata) and the characteristic painful swelling of Osgood-Schlatter disease of the tibial tubercle (see below).

IMAGING X-RAYS Anteroposterior and lateral views are routine; it is often useful also to obtain tangential ('skyline') patello-femoral views and intercondylar (or tunnel) views. The anteroposterior view should always be taken with the patient standing; unless the femoro-tibial compartment is loaded, narrowing of the articular space may be missed. Both knees should be x-rayed, so as to compare the abnormal with the normal side. Tibio-femoral alignment can be measured on fulllength standing views. Normal indices have also been established for patellar height and patello-femoral congruence. These features are discussed in the relevant sections of the chapter. OTHER FORMS OF IMAGING Radioscintigraphy may show increased activity in the subarticular bone in early osteoarthritis. It is also helpful in showing 'hot spots' due to infection after joint replacement. CT is useful for showing patello-femoral congruence at various angles of flexion. MRI provides a reliable means of diagnosing lateral and medial meniscal tears and cruciate ligament injuries (Oei et al., 2003). It is also helpful in identifying the early stages of osteoarticular lesions and osteonecrosis of the femoral or tibial condyles

ARTHROSCOPY Arthroscopy is useful: (1) to establish or refine the accuracy of diagnosis; (2) to help in deciding whether to operate, or to plan the operative approach with more precision; (3) to record the progress of a knee disorder; and (4) to perform certain operative procedures. Arthroscopy is not a substitute for clinical examination; a detailed history and meticulous assessment of the physical signs are indispensable preliminaries and remain the sheet anchor of diagnosis. However, arthroscopy is especially helpful in diagnosing meniscal injuries - and dealing with them at the same time. Full asepsis is essential.

SIGNS WITH THE PATIENT LYING PRONE Scars or lumps in the popliteal fossa are noted. If there is a swelling, is it in the midline (most likely a bulging capsule) or to one side (possibly a bursa)? A semimembranous bursa is usually just above the joint line, a Baker's cyst below it. The popliteal fossa is carefully palpated. If there is a lump, where does it originate? Does it pulsate? Can it be emptied into the joint?

Apley's test With the patient prone the knee is flexed to 90 degrees and rotated while a compression force is applied; this, the grinding test, reproduces symptoms if a meniscus is torn. Rotation is then repeated while the leg is pulled upwards with the surgeon's knee holding the thigh down; this, the distraction test, produces increased pain only if there is ligament damage. Lachman's test The Lachman test can be readily performed with the patient prone

ment of anterior knee pain. Another predisposing factor is a high-riding patella (patella alta); compressive force on the patellar articular surface during flexion and extension is likely to be greater than normal. Patella alta is best measured on the lateral x-ray). Lastly, the structures around the knee should be carefully examined for other sources of pain, and the hip is examined to exclude referred pain. Imaging X-ray examination should include skyline views of the patella, which may show abnormal tilting or subluxation, and a lateral view with the knee half-flexed to see if the patella is high or small. The most accurate way of showing and measuring patello-femoral malposition is by CT or MRI with the knees in full extension and varying degrees of flexion.

Arthroscopy Cartilage softening is common in asymptomatic knees, and painful knees may show no abnormality. However, arthroscopy is useful in excluding other causes of anterior knee pain; it can also serve to gauge patello-femoral congruence, alignment and tracking. Differential diagnosis Other causes of anterior knee pain must be excluded before finally accepting the diagnosis of patellofemoral pain syndrome (see Table 20.1). Even then, the exact cause of the syndrome must be established before treatment: e.g. is it abnormal posture, overuse, patellar malalignment, subluxation or some abnormality in the shape of the bones?

Imaging Plain x-rays may show a line of demarcation around a lesion in situ, usually in the lateral part of the medial femoral condyle. This site is best displayed in special intercondylar (tunnel) views, but even then a small lesion or one situated far back may be missed. Once the fragment has become detached, the empty hollow may be seen - and possibly a loose body elsewhere in the joint. Radionuclide scans show increased activity around the lesion, and MRI consistently shows an area of low signal intensity in the T1 weighted images; the adjacent bone may also appear abnormal, probably due to oedema. These investigations usually indicate whether the fragment is 'stable' or 'loose'. MRI may also allow early prediction of whether the lesion will heal or no

Arthroscopy With early lesions the articular surface looks intact, but probing may reveal that the cartilage is soft. Loose segments are easily visualized. Differential diagnosis Avascular necrosis of the femoral condyle - usually associated with corticosteroid therapy or alcohol abuse - may result in separation of a localized osteocartilaginous fragment. However, it is seen in an older age group and on x-ray the lesion is always on the dome of the femoral condyle, and this distinguishes it from osteochondritis dissecans.

Treatment Treatment is conservative in the first instance and consists of measures to reduce loading of the joint and analgesics for pain. If symptoms or signs increase, operative treatment may be considered. Surgical options include arthroscopic debridement, drilling with or without bone grafting, core decompression of the femoral condyle at a distance from the lesion, and (for patients with persistent symptoms and well-marked articular surface damage) a valgus osteotomy or unicompartmental arthroplasty. Resurfacing with osteochondral allografts has also been employed, with variable results.

CHARCOT'S DISEASE Charcot's disease (neuropathic arthritis) is a rare cause of joint destruction. Because of loss of pain sensibility and proprioception, the articular surface breaks down and the underlying bone crumbles. Fragments of bone and cartilage are deposited in the hypertrophic synovium and may grow into large masses. The capsule is stretched and lax, and the joint becomes progressively unstable. Clinical features The patient chiefly complains of instability; pain (other than tabetic lightning pains) is unusual. The joint is swollen and often grossly deformed. It feels like a bag of bones and fluid but is neither warm nor tender. Movements beyond the normal limits, without pain, are a notable feature. Radiologically the joint is subluxated, bone destruction is obvious and irregular calcified masses can be seen. Treatment Patients often seem to manage quite well despite the bizarre appearances. However, marked instability may demand treatment - usually a moulded splint or caliper will do - and occasionally pain becomes intolerable. Arthrodesis is feasible but fixation is difficult and fusion is very slow. Replacement arthroplasty is not indicated.

Treatment If the symptoms warrant operation, the cyst may be removed. In the past this was usually combined with total meniscectomy, in order to prevent an inevitable recurrence of the cyst. However, it is quite feasible to examine the meniscus by arthroscopy, remove only the torn or damaged portion and then decompress the cyst from within the joint. The recurrence rate following such arthroscopic surgery is negligible (Parisien, 1990).

CHRONIC LIGAMENTOUS INSTABILITY The knee is a complex hinge which depends heavily on its ligaments for medio-lateral, anteroposterior and rotational stability. Ligament injuries, from minor strains through partial ruptures to complete tears, are common in sportsmen, athletes and dancers. Whatever the nature of the acute injury, the victim may be left with chronic instability of the knee - a sense of the joint wanting to give way, or actually giving way, during unguarded activity. Sometimes this is accompanied by pain and recurrent episodes of swelling. There may be a meniscal tear, but meniscectomy is likely to make matters worse; sometimes patients present with meniscectomy scars on both sides of the knee! Examination should include special tests for ligamentous instability as well as radiological investigation and arthroscopy. It is important not only to establish the nature of the lesion but also to measure the level of functional impairment against the needs and demands of the individual patient before advocating treatment. The subject is dealt with in detail in Chapter 30.

Pathology The lower, lateral surface of the medial femoral condyle is usually affected, rarely the lateral condyle, and still more rarely the patella. An area of subchondral bone becomes avascular and within this area an ovoid osteocartilaginous segment is demarcated from the surrounding bone. At first the overlying cartilage is intact and the fragment is stable; over a period of months the fragment separates but remains in position; finally the fragment breaks free to become a loose body in the joint. The small crater is slowly filled with fibrocartilage, leaving a depression on the articular surface.

Classification Osteochondritis dissecans of the knee is classified according to anatomical location, arthroscopic appearance, scintigraphic or MRI findings and chronological age. For prognostic and treatment purposes it is divided into juvenile and adult forms, either stable or unstable (Kocher et al., 2006). Clinical features The patient, usually a male aged 15-20 years, presents with intermittent ache or swelling. Later, there are attacks of giving way such that the knee feels unreliable; 'locking' sometimes occurs. The quadriceps muscle is wasted and there may be a small effusion. Soon after an attack there are two signs that are almost diagnostic: (1) tenderness localized to one femoral condyle; and (2) Wilson's sign: if the knee is flexed to 90 degrees, rotated medially and then gradually straightened, pain is felt; repeating the test with the knee rotated laterally is painless.

RECURRENT DISLOCATION OF THE PATELLA Acute dislocation of the patella is dealt with in Chapter 30. In 15-20 per cent of cases (mostly children) the first episode is followed by recurrent dislocation or subluxation after minimal stress. This is due, in some measure, to disruption or stretching of the ligamentous structures which normally stabilize the extensor mechanism. However, in a significant proportion of cases there is no history of an acute strain and the initial episode is thought to have occurred 'spontaneously'. It is now recognized that in all cases of recurrent dislocation, but particularly in the latter group, one or more predisposing factors are often present: (1) generalized ligamentous laxity; (2) under - development of the lateral femoral condyle and flattening of the intercondylar groove; (3) maldevelopment of the patella, which may be too high or too small; (4) valgus deformity of the knee; (5) external tibial torsion; or (6) a primary muscle defect. Repeated dislocation damages the contiguous articular surfaces of the patella and femoral condyle; this may result in further flattening of the condyle, so facilitating further dislocations. Dislocation is almost always towards the lateral side; medial dislocation is seen only in rare iatrogenic cases following overzealous lateral release or medial transposition of the patellar tendon.

Clinical features Girls are affected more commonly than boys and the condition may be bilateral. Dislocation occurs unexpectedly when the quadriceps muscle is contracted with the knee in flexion. There is acute pain, the knee is stuck in flexion and the patient may fall to the ground. Although the patella always dislocates laterally, the patient may think it has displaced medially because the uncovered medial femoral condyle stands out prominently. If the knee is seen while the patella is dislocated, the diagnosis is obvious. There is a lump on the lateral side, while the front of the knee (where the patella ought to be) is flat. The tissues on the medial side are tender, the joint may be swollen and aspiration may reveal a blood-stained effusion. More often the patella has reduced by the time the patient is seen. Tenderness and swelling may still be present and the apprehension test is positive: if the patella is pushed laterally with the knee slightly flexed, the patient resists and becomes anxious, fearing another dislocation. The patient will normally volunteer a history of previous dislocation. Between attacks the patient should be carefully examined for features that are known to predispose to patellar instability (see above).

Slight over-correction should be aimed for as some recurrence is inevitable. In severe cases it may be necessary also to elevate the depressed medial tibial plateau using a wedge of bone taken from the femur. If a bony bar has formed, it can be excised and replaced by a free fat graft. In older children it may be easier to perform a surgical correction and then (if necessary) lengthen the tibia by the Ilizarov method. All these procedures should be accompanied by fasciotomy to reduce the risk of a postoperative compartment syndrome

DEFORMITIES OF THE KNEE IN ADULTS GENU VARUM AND GENU VALGUM Angular deformities are common in adults (usually bow legs in men and knock knees in women). They may be the sequel to childhood deformity and if so usually cause no problems. However, if the deformity is associated with joint instability, this can lead to osteoarthritis - of the medial compartment in varus knees and the lateral compartment in valgus knees. Genu valgum may also cause abnormal tracking of the patella and predispose to patello-femoral osteoarthritis. Even in the absence of overt osteoarthritis, if the patient complains of severe pain, or if there are clinical or radiological signs of joint damage, a 'prophylactic' osteotomy can be performed - above the knee for valgus deformity and below the knee for varus. Preoperative planning should include radiographic measurements to determine the mechanical and anatomical axes of both bones and the lower limb, as well as estimation of the centre of rotation of angulation

Pathology Cartilage breakdown usually starts in an area of excessive loading. Thus, with longstanding varus the changes are most marked in the medial compartment. The characteristic features of cartilage fibrillation, sclerosis of the subchondral bone and peripheral osteophyte formation are usually present; in advanced cases the articular surface may be denuded of cartilage and underlying bone may eventually crumble. Chondrocalcinosis is common, but whether this is cause or effect - or quite unrelated - remains unknown.

Clinical features Patients are usually over 50 years old; they tend to be overweight and may have longstanding bow-leg deformity. Pain is the leading symptom, worse after use, or (if the patello-femoral joint is affected) on stairs. After rest, the joint feels stiff and it hurts to 'get going' after sitting for any length of time. Swelling is common, and giving way or locking may occur. On examination there may be an obvious deformity (usually varus) or the scar of a previous operation. The quadriceps muscle is usually wasted. Except during an exacerbation, there is little fluid and no warmth; nor is the synovial membrane thickened. Movement is somewhat limited and is often accompanied by patello-femoral crepitus. It is useful to test movement applying first a varus and then a valgus force to the knee; pain indicates which tibio-femoral compartment is involved. Pressure on the patella may elicit pain. The natural history of osteoarthritis is one of alternating 'bad spells' and 'good spells'. Patients may experience long periods of lesser discomfort and only moderate loss of function, followed by exacerbations of pain and stiffness (perhaps after unaccustomed activity)

OSTEONECROSIS Osteonecrosis of the knee, though not as common as femoral head necrosis, has the same aetiological and pathogenetic background (see Chapter 6). The usual site is the dome of one of the femoral condyles, but occasionally the medial tibial condyle is affected. Two main categories are identified: (1) osteonecrosis associated with a definite background disorder [e.g. corticosteroid therapy, alcohol abuse, sickle-cell disease, hyperbaric decompression sickness, systemic lupus erythematosus (SLE) or Gaucher's disease], and (2) 'spontaneous' osteonecrosis of the knee, popularly known by the acronym SONK, which is due to a small insufficiency fracture of a prominent part of the osteoarticular surface in osteoporotic bone; the vascular supply to the free fragment is compromised (Yamamoto and Bullough, 2000). A third type, postmeniscectomy osteonecrosis, has been reported; its prevalence and pathophysiology are still unclear (Patel et al., 1998).

Clinical features Patients are usually over 60 years old and women are affected three times more often than men. Typically they give a history of sudden, acute pain on the medial side of the joint. Pain at rest also is common. On examination there is usually a small effusion, but the classic feature is tenderness on pressure upon the medial femoral or tibial condyle rather than along the joint line proper. The patient may offer a history of similar symptoms in the hip or the shoulder. Whether or not this

Most of the meniscus is avascular and spontaneous repair does not occur unless the tear is in the outer third, which is vascularized from the attached synovium and capsule. The loose tag acts as a mechanical irritant, giving rise to recurrent synovial effusion and, in some cases, secondary osteoarthritis

Clinical features The patient is usually a young person who sustains a twisting injury to the knee on the sports field. Pain (usually on the medial side) is often severe and further activity is avoided; occasionally the knee is 'locked' in partial flexion. Almost invariably, swelling appears some hours later, or perhaps the following day. With rest the initial symptoms subside, only to recur periodically after trivial twists or strains. Sometimes the knee gives way spontaneously and this is again followed by pain and swelling. It is important to remember that in patients aged over 40 the initial injury may be unremarkable and the main complaint is of recurrent 'giving way' or 'locking'. 'Locking' - that is, the sudden inability to extend the knee fully - suggests a bucket-handle tear. The patient sometimes learns to 'unlock' the knee by bending it fully or by twisting it from side to side. On examination the joint may be held slightly flexed and there is often an effusion. In longstanding cases the quadriceps will be wasted. Tenderness is localized to the joint line, in the vast majority of cases on the medial side. Flexion is usually full but extension is often slightly limited. Between attacks of pain and effusion there is a

here, means either direct stress on a load-bearing facet or sheer stresses in the depths of the articular cartilage at the boundary between high-contact and low-contact areas (Goodfellow et al., 1976). Personality and chronic pain response issues must also be considered (Thomee et al., 1999). Patello-femoral overload leads to changes in both the articular cartilage and the subchondral bone, not necessarily of parallel degree. Thus, the cartilage may look normal and show only biochemical changes such as overhydration or loss of proteoglycans, while the underlying bone shows reactive vascular congestion (a potent cause of pain). Or there may be obvious cartilage softening and fibrillation, with or without subarticular intraosseous hypertension. This would account for the variable relationship between (1) malalignment syndrome, (2) cartilage softening, (3) subchondral vascular congestion and (4) anterior knee pain. Cartilage fibrillation usually occurs on the medial patellar facet or the median ridge, remains confined to the superficial zones and generally heals spontaneously (Bentley, 1985). It is not a precursor of progressive osteoarthritis in later life. Occasionally the lateral facet is involved - Ficat's 'hyperpression zone' syndrome - and this may well be progressive (Ficat and Hungerford, 1977).

Clinical features The patient, often a teenage girl or an athletic young adult, complains of pain over the front of the knee or 'underneath the knee-cap'. Occasionally there is a history of injury or recurrent displacement. Symptoms are aggravated by activity or climbing stairs, or when standing up after prolonged sitting. The knee may give way and occasionally swells. It sometimes 'catches' but this is not true locking. Often both knees are affected. At first sight the knee looks normal but careful examination may reveal malalignment or tilting of the patellae. Other signs include quadriceps wasting, fluid in the knee, tenderness under the edge of the patella and crepitus on moving the knee. Patello-femoral pain is elicited by pressing the patella against the femur and asking the patient to contract the quadriceps - first with central pressure, then compressing the medial facet and then the lateral. If, in addition, the apprehension test is positive, this suggests previous subluxation or dislocation. Patellar tracking can be observed with the patient seated on the edge of the couch, flexing and extending the knee against resistance; in some cases subluxation is obvious. With the patient sitting or lying supine, patellar alignment can be gauged by measuring the quadriceps angle, or Q-angle - the angle subtended by the line of quadriceps pull (a line running from the anterior superior iliac spine to the middle of the patella) and the line of the patellar ligament. It normally averages 14-17 degrees and an angle of more than 20 degrees is regarded as a predisposing factor in the develop

THE DIAGNOSTIC CALENDAR While most disorders of the knee can occur at any age, certain conditions are more commonly encountered during specific periods of life

Congenital knee disorders may be present at birth or may become apparent only during the first or second decade of life. Adolescents with anterior knee pain are usually found to have chondromalacia patellae, patellar instability, osteochondritis or a plica syndrome. But remember - knee pain may be referred from the hip! Young adults engaged in sports are the most frequent victims of meniscal tears and ligament injuries. Examination should include a variety of tests for ligamentous instability that would be quite inappropriate in elderly patients. Patients above middle age with chronic pain and stiffness probably have osteoarthritis. With primary osteoarthritis of the knees, other joints also are often affected; polyarthritis does not necessarily (nor even most commonly) mean rheumatoid arthritis.

Clinical features The lateral meniscus is affected much more frequently than the medial. The patient complains of an ache or a small lump at the side of the joint. Symptoms may be intermittent, or worse after activity. On examination the lump is situated at or slightly below the joint line, usually anterior to the collateral ligament. It is seen most easily with the knee slightly flexed; in some positions it may disappear altogether. Lateral cysts are often so firm that they are mistaken for a solid swelling. Medial cysts are usually larger and softer.

Differential diagnosis Apart from cysts, various conditions may present with a small lump along the joint line. A ganglion is quite superficial, usually not as 'hard' as a cyst, and unconnected with the joint. Calcific deposits in the collateral ligament usually appear on the medial side, are intensely painful and tender, and often show on the x-ray. A prolapsed, torn meniscus occasionally presents as a rubbery, irregular lump at the joint line. In some cases the distinction from a 'cyst' is largely academic. Various tumours, both of soft tissue (lipoma, fibroma) and of bone (osteochondroma), may produce a medial or lateral joint lump. Careful examination will show that the lump does not arise from the joint itself.

disconcerting paucity of signs. The history is helpful, and McMurray's test, Apley's grinding test or the Thessaly test may be positive. Investigations Plain x-rays are usually normal, but MRI is a reliable method of confirming the clinical diagnosis, and may even reveal tears that are missed by arthroscopy. Arthroscopy has the advantage that, if a lesion is identified, it can be treated at the same time.

Differential diagnosis Loose bodies in the joint may cause true locking. The history is much more insidious than with meniscal tears and the attacks are variable in character and intensity. A loose body may be palpable and is often visible on x-ray. Recurrent dislocation of the patella causes the knee to give way; typically the patient is caught unawares and collapses to the ground. Tenderness is localized to the medial edge of the patella and the apprehension test is positive. Fracture of the tibial spine follows an acute injury and may cause a block to full extension. However, swelling is immediate and the fluid is blood-stained. X-ray may show the fracture. A partial tear of the medial collateral ligament may heal with adhesions where it is attached to the medial meniscus, so that the meniscus loses mobility. The patient complains of recurrent attacks of pain and giving way, followed by tenderness on the medial side. Sleep may be disturbed if the medial side rests upon the other knee or the bed. As with a meniscus injury, rotation is painful; but unlike a meniscus lesion, the grinding test gives less pain and the distraction test more pain. A torn anterior cruciate ligament can cause chronic instability, with a sense of the knee 'giving way' or buckling when the patient turns sharply towards the side of the affected knee. Careful examination should reveal signs of rotational instability, a positive Lachman test or a positive anterior drawer sign. MRI or arthroscopy will settle any doubts.

Lateral release The lateral knee capsule and extensor retinaculum are divided longitudinally, either open or arthroscopically. This sometimes succeeds on its own (particularly if significant patellar tilting can be demonstrated on x-ray or MRI), but more often patello-femoral realignment will be needed as well. Proximal realignment This is achieved by a combined open release of the lateral retinaculum and reefing of the oblique part of the vastus medialis

Distal realignment The distal soft-tissue and bony realignment procedures are described on page 563. They will improve the tracking angle but run the risk of increasing patello-femoral contact pressures and thus aggravating the patient's symptoms. Distal elevation of the patellar ligament In Maquet's (1976) tibial tubercle advancement operation the tubercle, with the attached patellar ligament, is hinged forwards and held there with a bone-block. This has the effect of reducing patello-femoral contact pressures. Some patients resent the bump on the front part of the tibia and the operation may substitute a new set of complaints for the old. Alternatively, the Fulkerson anteromedial tibial tubercle transfer and elevation can be used with satisfactory mid-term results

Deformity may be secondary to arthritis - usually varus in osteoarthritis and valgus in rheumatoid arthritis. In these cases the joint is often unstable and corrective osteotomy less predictable in its effect. Stress x-rays are essential in the assessment of these cases. Other causes of varus or valgus deformity are ligament injuries, malunited fractures and Paget's disease. Where possible, the underlying disorder should be dealt with; provided the joint is stable, corrective osteotomy may be all that is necessary.

GENU RECURVATUM (HYPEREXTENSION OF THE KNEE) Congenital recurvatum This may be due to abnormal intra-uterine posture; it usually recovers spontaneously. Rarely, gross hyperextension is the precursor of true congenital dislocation of the knee.

Locking is different from stiffness. The knee, quite suddenly, cannot be straightened fully, although flexion is still possible. This happens when a torn meniscus or loose body is caught between the articular surfaces. By wiggling the knee around, the patient may be able to 'unlock' it; sudden unlocking is the most reliable evidence that something mobile had previously obstructed full extension. Do not be misled by 'pseudo-locking', when movement is suddenly stopped by pain or the fear of impending pain. Deformity is seldom a leading symptom; patients are not keen to admit to having 'knock knees' or 'bandy legs'. However, a unilateral deformity, especially if it is progressive, will be more worrying.

Giving way, a feeling of instability, or a lack of trust in the knee suggests a mechanical disorder caused by ligamentous, meniscal or capsular injury, or simple muscle weakness. Giving way, particularly if it occurs when climbing up or down stairs, may also be due to patello-femoral pain or instability. Excessive use of an unstable knee produces post-exercise swelling (effusion or haemarthrosis) and diffuse pain within the joint. Limp may be due to either pain or instability. Loss of function manifests as a progressively diminishing walking distance, inability to run and difficulty going up and down steps. Squatting or kneeling may be painful, either because of pressure on the patellofemoral joint or because the knee cannot flex fully.

these children are normal in all other respects; the parents should be reassured and the child should be seen at intervals of 6 months to record progress. In the occasional case where, by the age of 10, the deformity is still marked (i.e. the intercondylar distance is more than 6 cm or the intermalleolar distance more than 8 cm), operative correction should be advised. Stapling of the physes on one or other side of the knee can be done to restrict growth on that side and allow correction of the deformity (the staples are removed once the knee has over-corrected slightly); there is a risk, however, that normal growth will not resume when the staples are removed.

Hemi-epiphysodesis (fusion of one-half of the growth plate) on the 'convex' side of the deformity will achieve similar correction; this requires careful timing guided by charting the child's bone age and estimating the corrective effect of arresting further growth on one side of the bone. Corrective osteotomy (supracondylar osteotomy for valgus knees and high tibial osteotomy for varus knees) may sound sensible; however, the child (and the parents) will have to put up with the 'deformity' until growth is complete before undergoing the operation, otherwise there is a risk of the deformity recurring while the child is still growing

An opening wedge valgus osteotomy on the medial side offers some advantages: the ability to adjust the degree of correction intra-operatively and the option to correct deformities in the sagittal plane as well as the coronal plane; it also makes it unnecessary to disrupt the tibio-fibular joint. However, there are also disadvantages: the newly-created gap must be filled with a bone graft and a long period of restricted weightbearing is needed after the procedure; there is also a higher rate of non-union or delayed union. These drawbacks can be mitigated by stabilizing the fragments with an external fixator applied to the medial side, waiting for about 5 days and then opening the gap very gradually, allowing it to fill with callus (hemicallotasis). Cast immobilization is unnecessary. The external fixator usually remains in place for 10-12 weeks.

If a varus osteotomy is required - usually for active patients with isolated lateral compartment disease and valgus deformity of the knee - this is performed at the supracondylar level of the femur. The method most commonly employed is a medial closing wedge osteotomy, designed to place the mechanical axis at zero. The fragments should be firmly fixed with a blade-plate; in many cases postoperative cast immobilization will also be needed.

Clinical features Loose bodies may be symptomless. The usual complaint is attacks of sudden locking without injury. The joint gets stuck in a position which varies from one attack to another. Sometimes the locking is only momentary and usually the patient can wriggle the knee until it suddenly unlocks. The patient may be aware of something 'popping in and out of the joint'.

In adolescents, a loose body is usually due to osteochondritis dissecans, rarely to injury. In adults osteoarthritis is the most frequent cause. Only rarely is the patient seen with the knee still locked. Sometimes, especially after the first attack, there is synovitis or there may be evidence of the underlying cause. A pedunculated loose body may be felt; one that is truly loose tends to slip away during palpation (the well-named 'joint mouse'). X-ray Most loose bodies are radio-opaque. The films also show an underlying joint abnormality

Lax ligaments Normal people with generalized joint laxity tend to stand with their knees back-set. Prolonged traction, especially on a frame, or holding the knee hyperextended in plaster, may overstretch ligaments, leading to permanent hyperextension deformity. Ligaments may also become overstretched following chronic or recurrent synovitis (especially in rheumatoid arthritis), the hypotonia of rickets, the flailness of poliomyelitis or the insensitivity of Charcot's disease.

In paralytic conditions such as poliomyelitis, recurvatum is often seen in association with fixed equinus of the ankle: in order to set the foot flat on the ground, the knee is forced into hyperextension. In moderate degrees, this may actually be helpful (e.g. in stabilizing a knee with weak extensors). However, if excessive and prolonged, it may give rise to a permanent deformity. If bony correction is undertaken, the knee should be left with some hyperextension to preserve the stabilizing mechanism. If quadriceps power is poor, the patient may need a caliper. Severe paralytic hyperextension can be treated by fixing the patella into the tibial plateau, where it acts as a bone block (Men et al., 1991). Miscellaneous Other causes of recurvatum are growth plate injuries and malunited fractures. These can be safely corrected by osteotomy.

because cartilage lysis is prevented by the presence of a plasmin inhibitor in the synovial exudate. Late features If the disease is allowed to persist the joint surfaces will gradually be eroded and the knee joint will become deformed. The classical picture in neglected cases is a composite deformity: posterior and lateral subluxation or dislocation, external rotation and fixed flexion. Diagnosis Monarticular rheumatoid synovitis, or juvenile chronic arthritis, may closely resemble tuberculosis. A synovial biopsy may be necessary to establish the diagnosis. Treatment General antituberculous chemotherapy should be given for 12-18 months (see page 49). In the active stage the knee is rested in a bed splint. The synovitis usually subsides, but if it does not do so after a few weeks' treatment, then surgical debridement will be needed. All obviously diseased and necrotic tissue is removed and bone abscesses are evacuate

In the healing stage the patient is allowed up wearing a weight-relieving caliper. Gradually this is left off, but the patient is kept under observation for any sign of recurrent inflammation. If the articular cartilage has been spared, movement can be encouraged and weightbearing is slowly resumed. However, if the articular surface is destroyed, immobilization is continued until the joint stiffens. In the aftermath the joint may be painful; it is then best arthrodesed, but in children this is usually postponed until growth is almost completed. The ideal position for fusion is 10-15 degrees of flexion, 7 degrees of valgus and 5 degrees of external rotation. In some cases, once it is certain that the disease is quiescent, joint replacement may be feasible.

RHEUMATOID ARTHRITIS Occasionally, rheumatoid arthritis starts in the knee as a chronic monarticular synovitis. Sooner or later, however, other joints become involved. Clinical features The general features of rheumatoid disease are described in Chapter 3. The early stage is characterized by synovitis; rheumatoid disease occasionally starts with involvement of a single joint. The patient complains of pain and chronic swelling of the knee; there is usually an effusion and the thigh muscles may be wasted. The thickened synovium is often palpable. Unless there are obvious signs of an inflammatory polyarthritis, the condition has to be distinguished from other types of inflammatory monarthritis, such as gout, Reiter's disease and tuberculosis; biopsy and microbiological investigations may be needed. During this early stage, while the joint is still stable and the muscles are reasonably strong, there is a danger of rupturing the posterior capsule; the joint contents are extruded into a large posterior bursa or between the muscle planes of the calf, causing sudden pain and swelling which closely mimic the features of calf vein thrombosis. As the disease progresses the knee becomes increasingly unstable, muscle wasting is marked and there is some loss of flexion and extension. X-rays may show diminution of the joint space, osteopaenia and marginal erosions. The picture is easily distinguishable from that of osteoarthritis by the complete absence of osteophytes.

In the late stage pain and disability are usually severe. In some patients stiffness is so marked that the patient has to be helped to stand and the joint has only a jog of painful movement. In others, cartilage and bone destruction predominate and the joint becomes increasingly unstable and deformed, usually in fixed flexion and valgus. X-rays reveal the bone destruction characteristic of advanced disease. Treatment The majority of patients can be managed by conservative measures. In addition to general treatment with anti-inflammatory and disease-modifying drugs, local splintage and injection of triamcinolone usually help to reduce the synovitis. A more prolonged effect may be obtained by injecting radiocolloids such as yttrium- 90 (90Y). OPERATIVE TREATMENT Synovectomy and debridement Only if other measures fail to control the synovitis (which nowadays is rare) is synovectomy indicated. This can be done very effectively by arthroscopy. Articular pannus and cartilage tags are removed at the same time. Postoperatively, any haematoma must be drained and movements are commenced as soon as pain has subsided

COMPLICATIONS Intra-articular effusions and small haemarthroses are fairly common but seldom troublesome. Reflex sympathetic dystrophy (which may resemble a low-grade infection during the weeks following arthroscopy) is sometimes troublesome. It usually settles down with physiotherapy and treatment with non-steroidal anti-inflammatory drugs; occasionally it requires more radical treatment (see pages 261 and 723).

LIGAMENT RECONSTRUCTION The collateral and cruciate ligaments and the knee capsule are important constraints which allow normal knee function; laxity or rupture of these structures, either singly or in combination, is often the source of recurrent episodes of 'giving way'. Although a significant proportion of such injuries are treated non-operatively, complete ruptures may require surgery in 'high-demand' individuals. Surgery for ligament reconstruction includes: 1. Repair, usually for collateral ligament midsubstance ruptures when they are found in combination with cruciate ligament injuries. This repair can be a simple end-to-end suture. 2. Substitution, usually for anterior cruciate ruptures: the semitendinosus and gracilis, either one or two bundle technique, can be carefully anchored to the femur and tibia ensuring that stability is restored without loss of knee movement. Another method is to use an autologous graft from the patellar tendon. 3. Tenodesis, using a variety of tendons which are passed either through bony or soft-tissue tunnels to 'check' the abnormal movement resulting from ligament rupture

DISCOID LATERAL MENISCUS In the fetus the meniscus is not semilunar but disclike; if this shape persists, symptoms are likely. A young patient complains that, without any history of injury, the knee gives way and 'thuds' loudly. A characteristic clunk may be felt at 110 degrees as the knee is bent and at 10 degrees as it is being straightened. The diagnosis is easily confirmed by MRI. If there is only a clunk, treatment is not essential. If pain is disturbing, the meniscus may be excised, though a more attractive procedure is arthroscopic partial excision leaving a normally shaped meniscus (Dimakopoulos and Patel, 1990

MENISCAL CYSTS Cysts of the menisci are probably traumatic in origin, arising from either a small horizontal cleavage tear or repeated squashing of the peripheral part of the meniscus. It is also suggested that synovial cells infiltrate into the vascular area between meniscus and capsule and there multiply. The multilocular cyst contains gelatinous fluid and is surrounded by thick fibrous tissue

Outcome Neither a meniscal tear by itself nor removal of the meniscus necessarily leads to secondary osteoarthritis. However, the likelihood is increased if the patient has (a) a pre-existing varus deformity of the knee, (b) signs of cruciate ligament insufficiency or (c) features elsewhere of a generalized osteoarthritis

MENISCAL DEGENERATION Patients over 45 years old may present with symptoms and signs of a meniscal tear. Often, though, they can recall no preceding injury. At arthroscopy there may be a horizontal cleavage in the medial meniscus - the characteristic 'degenerative' lesion - or detachment of the anterior or posterior horn without an obvious tear. Associated osteoarthritis or chrondrocalcinosis is common. A detached anterior or posterior horn can be sutured firmly in place. Meniscectomy is indicated only if symptoms are marked or if, at arthroscopy, there is a major tear causing mechanical block.

Cruciate ligaments Routine tests for cruciate ligament stability are based on examining for abnormal gliding movements in the sagittal plane. With both knees flexed 90 degrees and the feet resting on the couch, the upper tibia is inspected from the side; if its upper end has dropped back, or can be gently pushed back, this indicates a tear of the posterior cruciate ligament (the 'sag sign'). With the knee in the same position, the foot is anchored by the examiner sitting on it (provided this is not painful); then, using both hands, the upper end of the tibia is grasped firmly and rocked backwards and forwards to see if there is any anteroposterior glide (the 'drawer test'). Excessive anterior movement (a positive anterior drawer sign) denotes anterior cruciate laxity; excessive posterior movement (a positive posterior drawer sign) signifies posterior cruciate laxity.

More sensitive is the Lachman test, but this is difficult if the patient has big thighs (or the examiner has small hands). The patient's knee is flexed 20 degrees; with one hand grasping the lower thigh and the other the upper part of the leg, the joint surfaces are shifted backwards and forwards upon each other. If the knee is stable, there should be no gliding. In both the drawer test and Lachman test, note whether the endpoint of abnormal movement is 'soft' or 'hard'.

knee, the outlines of the joint margins, the patellar ligament, the collateral ligaments, the iliotibial band and the pes anserinus are then easily traced with the fingers. The point of maximum tenderness will suggest at least the anatomical site of pathology if not the precise diagnosis. Synovial thickening is best appreciated as follows: placing the knee in extension, the examiner grasps the edges of the patella in a pincer made of the thumb and middle finger, and tries to lift the patella forwards; normally the bone can be grasped quite firmly, but if the synovium is thickened the fingers simply slip off the edges of the patella.

Move Passive extension can be tested by the examiner simply holding both legs by the ankles and lifting them off the couch; the knees should straighten fully (or even into a few degrees of hyperextension) and symmetrically. Active extension can be roughly tested by the examiner slipping a hand under each knee and then asking the patient to force the knees into the surface of the couch; it is usually easy to feel whether the hands are trapped equally strongly on the two sides. Another way is to have the patient sitting on the edge of the couch with his or her legs hanging over the side and then asking them to extend each knee as far as possible; the test can be repeated with the patient extending the knees against resistance. Passive and active flexion are tested with the patient lying supine. Normally the heel can be pulled up close to the buttock, with the knee moving through a range of 0-150 degrees. The 'heel-to-buttock' distance is compared on the two sides.

prescribed for pain, and warmth (e.g. radiant heat or shortwave diathermy) is soothing. A simple elastic support may do wonders, probably by improving proprioception in an unstable knee. Intra-articular corticosteroid injections will often relieve pain, but this is a stopgap, and not a very good one, because repeated injections may permit (or even predispose to) progressive cartilage and bone destruction. New forms of medication have been introduced in recent years, particularly the oral administration of glucosamine and intra-articular injection of hyalourans. There is, as yet, no agreement about the long-term efficacy of these products

OPERATIVE TREATMENT Persistent pain unresponsive to conservative treatment, progressive deformity and instability are the usual indications for operative treatment. Arthroscopic washouts, with trimming of degenerate meniscal tissue and osteophytes, may give temporary relief; this is a useful measure when there are contraindications to reconstructive surgery. Patellectomy is indicated only in those rare cases where osteoarthritis is strictly confined to the patellofemoral joint. However, bear in mind that extensor power will be reduced and if a total joint replacement is later needed pain relief will be less predictable than usual (Paletta and Laskin, 1995).

Treatment CONSERVATIVE MANAGEMENT In the vast majority of cases the patient will be helped by adjustment of stressful activities and physiotherapy, combined with reassurance that most patients eventually recover without physiotherapy. Exercises are directed specifically at strengthening the medial quadriceps so as to counterbalance the tendency to lateral tilting or subluxation of the patella. Some patients respond to simple measures such as providing support for a valgus foot. Aspirin does no more than reduce pain, and corticosteroid injections should be avoided.

OPERATIVE TREATMENT Surgery should be considered only if (1) there is a demonstrable abnormality that is correctable by operation, or (2) conservative treatment has been tried for at least 6 months and (3) the patient is genuinely incapacitated. Operation is intended to improve patellar alignment and patello-femoral congruence and to reduce patello-femoral pressure. Various measures are employed: lateral release, with or without one of the realignment procedures illustrated in Figure 20.24, may be needed if there is any sign of patellar instability; other operations are the patellar ligament elevation procedure of Maquet and - as a last resort - patellectomy.

Exercises should be continued for at least 3 months, concentrating on strengthening the vastus medialis muscle. If recurrences are few and far between, conservative treatment may suffice; as the child grows older the patellar mechanism tends to stabilize. However, about 15 per cent of children with patellar instability suffer repeated and distressing episodes of dislocation and for these patients surgical reconstruction is indicated.

OPERATIVE TREATMENT The principles of operative treatment are (a) to repair or strengthen the medial patello-femoral ligaments, and (b) to realign the extensor mechanism so as to produce a mechanically more favourable angle of pull. This can be achieved in several ways (see Fig. 20.24). Direct medial patello-femoral ligament repair Occasionally it is possible to perform a direct repair of an attenuated medial patello-femoral ligament. Suprapatellar realignment (Insall) The lateral retinaculum and capsule are divided. The quadriceps tendon adjacent to the vastus medialis is split longitudinally to the level of the tibial tubercle; the free edge is then sutured over the middle of the patella, thus bringing vastus medialis distally and closer to the midline

Supracondylar osteotomy Realignment osteotomy is unlikely to have any protective effect in a disease which is marked by generalized cartilage erosion. However, if the knee is stable and pain-free but troublesome because of valgus and flexion deformity, a corrective supracondylar osteotomy is useful. Arthroplasty Total joint replacement is useful when joint destruction is advanced. However, it is less successful if the knee has been allowed to become very unstable or very stiff; timing of the operation is important.

OSTEOARTHRITIS The knee is the commonest of the large joints to be affected by osteoarthritis (see Chapter 5). Often there is a predisposing factor: injury to the articular surface, a torn meniscus, ligamentous instability or preexisting deformity of the hip or knee, to mention a few. However, in many cases no obvious cause can be found. Underlying all of these, there may also be a genetic component. Curiously, while the male:female distribution is more or less equal in white (Caucasian) peoples, black African women are affected far more frequently than their male counterparts. Osteoarthritis is often bilateral and in these cases there is a strong association with Heberden's nodes and generalized osteoarthritis.

Treatment Dealing with the locked knee Usually the knee 'unlocks' spontaneously; if not, gentle passive flexion and rotation may do the trick. Forceful manipulation is unwise (it may do more damage) and is usually unnecessary; after a few days' rest the knee may well unlock itself. However, if the knee does not unlock, or if attempts to unlock it cause severe pain, arthroscopy is indicated. If symptoms are not marked, it may be better to wait a week or two and let the synovitis settle down, thus making the operation easier; if the tear is confirmed, the offending fragment is removed. Conservative treatment If the joint is not locked, it is reasonable to hope that the tear is peripheral and can therefore heal spontaneously. After an acute episode, the joint is held straight in a plaster backslab for 3-4 weeks; the patient uses crutches and quadriceps exercises are encouraged. Operation can be put off as long as attacks are infrequent and not disabling and the patient is willing to abandon those activities that provoke them. MRI will show if the meniscus has healed.

Operative treatment Surgery is indicated (1) if the joint cannot be unlocked and (2) if symptoms are recurrent. For practical purposes, the lesion is often dealt with as part of the 'diagnostic' arthroscopy. Tears close to the periphery, which have the capacity to heal, can be sutured; at least one edge of the tear should be red (i.e. vascularized). In appropriate cases the success rate for both open and arthroscopic repair is almost 90 per cent. Tears other than those in the peripheral third are dealt with by excising the torn portion (or the bucket handle). Total meniscectomy is thought to cause more instability and so predispose to late secondary osteoarthritis; certainly in the short term it causes greater morbidity than partial meniscectomy and has no obvious advantages. Arthroscopic meniscectomy has distinct advantages over open meniscectomy: shorter hospital stay, lower costs and more rapid return to function. However, it is by no means free of complications (Sherman et al., 1986). Postoperative pain and stiffness are reduced by prophylactic non-steroidal anti-inflammatory drugs. Quadriceps-strengthening exercises are important

SWELLINGS AT THE BACK OF THE KNEE SEMIMEMBRANOSUS BURSA The bursa between the semimembranosus and the medial head of gastrocnemius may become enlarged in children or adults. It presents usually as a painless lump behind the knee, slightly to the medial side of the midline and most conspicuous with the knee straight. The lump is fluctuant but the fluid cannot be pushed into the joint, presumably because the muscles compress and obstruct the normal communication. The knee joint is normal. Occasionally the lump aches, and if so it may be excised through a transverse incision. However, recurrence is common and, as the bursa normally disappears in time, a waiting policy is perhaps wiser.

POPLITEAL 'CYST' Bulging of the posterior capsule and synovial herniation may produce a swelling in the popliteal fossa. The lump, which is usually seen in older people, is in the midline of the limb and at or below the level of the joint. It fluctuates but is not tender. Injection of radio-opaque medium into the joint, and x-ray, will show that the 'cyst' communicates with the joint. The condition was originally described by Baker, whose patients were probably suffering from tuberculous synovitis. Nowadays it is more likely to be caused by rheumatoid or osteoarthritis, but it is still often called a 'Baker's cyst'. Occasionally the 'cyst' ruptures and the synovial contents spill into the muscle planes causing pain and swelling in the calf - a combination which can easily be mistaken for deep vein thrombosis.

Chondroplasty Shaving of the patellar articular surface is usually performed arthroscopically using a power tool. Soft and fibrillated cartilage is removed, in severe cases down to the level of subchondral bone; the hope is that it will be replaced by fibrocartilage. The operation should be followed by lavage and can be combined with any of the realignment procedures.

Patellectomy This is a last resort, but patients with severe discomfort are grateful for the relief it brings after other operations have failed.

PATELLO-FEMORAL PAIN SYNDROME (CHONDROMALACIA OF THE PATELLA; PATELLOFEMORAL OVERLOAD SYNDROME) There is no clear consensus concerning the terminology, aetiology and treatment of pain and tenderness in the anterior part of the knee. This syndrome is common among active adolescents and young adults. It is often (but not invariably) associated with softening and fibrillation of the articular surface of the patella - chondromalacia patellae. Having no other pathological label, orthopaedic surgeons have tended to regard chondromalacia as the cause (rather than one of the effects) of the disorder. Against this are the facts that (1) chondromalacia is commonly found at arthroscopy in young adults who have no anterior knee pain, and (2) some patients with the typical clinical syndrome have no cartilage softening.

Pathogenesis and pathology Pain over the anterior aspect of the knee occurs as one of the symptoms in a number of well-recognized disorders, the commonest of which are bursitis, Osgood-Schlatter disease, a neuroma, plica syndromes, patello-femoral arthritis and tendinitis affecting either the insertion of the quadriceps tendon or the patellar ligament - Sinding-Larsen's disease. When these are excluded and no other cause can be found, one is left with a clinically recognizable syndrome that has earned the unsatisfactory label of 'anterior knee pain' or 'patello-femoral pain syndrome'. The basic disorder is probably mechanical overload of the patello-femoral joint. Rarely, a single injury (sudden impact on the front of the knee) may damage the articular surfaces. Much more common is repetitive overload due to either (1) malcongruence of the patello-femoral surfaces because of some abnormal shape of the patella or intercondylar groove, (2) malalignment of the lower extremity and/or the patella, (3) muscular imbalance of the lower extremity with decreased strength due to atrophy or inhibition, or relative weakness of the vastus medialis, which causes the patella to tilt, or subluxate, or bear more heavily on one facet than the other during flexion and

Compensatory deformities Varus, valgus and rotational deformities of the proximal femur may give rise to complex compensatory deformities of the knees and legs once the child starts to walk. Thus, persistent anteversion of the femoral neck may come to be associated with 'squinting knees' (the patellae face inwards when the hips are fully located), genu valgum, tibial torsion and valgus heels. It is essential to analyse all components of these deformities before focussing on the knees. Often they correct spontaneously by the end of growth, or if some elements persist, they cause little or no problem; only in severe cases - and after the most meticulous preoperative planning - are osteotomies undertaken

Pathological bow leg and knock knee Disorders which cause distorted epiphyseal and/or physeal growth may give rise to bow leg or knock knee; these include some of the skeletal dysplasias and the various types of rickets, as well as injuries of the epiphyseal and physeal growth cartilage. A unilateral deformity is likely to be pathological, but it is essential in all cases to look for signs of injury or generalized skeletal disorder. If angulation is severe, operative correction will be necessary, but it should be deferred until near the end of growth lest the deformity recur with further growth.

TEARS OF THE MENISCUS The meniscus consists mainly of circumferential fibres held by a few radial strands. It is, therefore, more likely to tear along its length than across its width. The split is usually initiated by a rotational grinding force, which occurs (for example) when the knee is flexed and twisted while taking weight; hence the frequency in footballers. In middle life, when fibrosis has restricted mobility of the meniscus, tears occur with relatively little force

Pathology The medial meniscus is affected far more frequently than the lateral, partly because its attachments to the capsule make it less mobile. Tears of both menisci may occur with severe ligament injuries In 75 per cent of cases the split is vertical in the length of the meniscus. If the separated fragment remains attached front and back, the lesion is called a bucket-handle tear. The torn portion sometimes displaces towards the centre of the joint and becomes jammed between femur and tibia, causing a block to extension ('locking'). If the tear emerges at the free edge of the meniscus, it leaves a tongue based anteriorly (an anterior horn tear) or posteriorly (a posterior horn tear). Horizontal tears are usually 'degenerative' or due to repetitive minor trauma. Some are associated with meniscal cysts (see below).

THE PLICA SYNDROME A plica is the remnant of an embryonic synovial partition which persists into adult life. During development of the embryo, the knee is divided into three cavities - a large suprapatellar pouch and beneath this the medial and lateral compartments - separated from each other by membranous septa. Later these partitions disappear, leaving a single cavity, but part of a septum may persist as a synovial pleat or plica (from the Latin plicare = fold). This is found in over 20 per cent of people, usually as a median infrapatellar fold (the ligamentum mucosum), less often as a suprapatellar curtain draped across the opening of the suprapatellar pouch or a mediopatellar plica sweeping down the medial wall of the joint.

Pathology The plica in itself is not pathological. But if acute trauma, repetitive strain or some underlying disorder (e.g. a meniscal tear) causes inflammation, the plica may become oedematous, thickened and eventually fibrosed; it then acts as a tight bowstring impinging on other structures in the joint and causing further synovial irritation. Clinical features An adolescent or young adult complains of an ache in the front of the knee (occasionally both knees), with intermittent episodes of clicking or 'giving way'. There may be a history of trauma or markedly increased activity. Symptoms are aggravated by exercise or climbing stairs, especially if this follows a long period of sitting. On examination there may be muscle wasting and a small effusion. The most characteristic feature is tenderness near the upper pole of the patella and over the femoral condyle. Occasionally the thickened band can be felt. Movement of the knee may cause catching or snapping.

Realignment osteotomy is often successful in relieving symptoms and staving off the need for 'end-stage' surgery. The ideal indication is a 'young' patient (under 50 years) with a varus knee and osteoarthritis confined to the medial compartment: a high tibial valgus osteotomy will redistribute weight to the lateral side of the joint. The degree and accuracy of angular correction are the most important determinants of mid- and long-term clinical outcome

Replacement arthroplasty is indicated in older patients with progressive joint destruction. This is usually a 'resurfacing' procedure, with a metal femoral condylar component and a metal-backed polyethylene table on the tibial side. If the disease is largely confined to one compartment, a unicompartmental replacement can be done as an alternative to osteotomy. With modern techniques, and meticulous attention to anatomical alignment of the knee, the results of replacement arthroplasty are excellent. Arthrodesis is indicated only if there is a strong contraindication to arthroplasty (e.g. previous infection) or to salvage a failed arthroplasty

INDICATIONS Deformity of the knee Severe varus or valgus deformity (e.g. due to a growth defect, epiphyseal injury or a malunited fracture) may of itself call for a corrective osteotomy, and the operation may also prevent or delay the development of osteoarthritis. Localized articular surface destruction Patients with unicompartmental osteoarthritis or advanced localized osteonecrosis, particularly when this is associated with deformity in the coronal plane, may benefit from an osteotomy which offloads the affected area. Provided the joint is stable and has retained a reasonable range of movement, this offers an acceptable alternative to a unicompartmental arthroplasty. Usually it is the medial compartment that is affected and the knee exhibits a varus deformity. By realigning the joint, load is transferred from the medial compartment to the centre or a little towards the lateral side. Slight over-correction may further offload the medial compartment but marked valgus should be avoided as this will rapidly lead to cartilage loss in the lateral compartment.

Published results suggest that the operation provides substantial improvements in pain and function over a 7-10-year period (Dowd et al., 2006). Intra-articular reconstructions The introduction of meniscal and articular cartilage reconstruction techniques has led to considerable interest in applying the favourable biomechanical effects of osteotomy to the younger patient who has a full-thickness chondral lesion or an absent meniscus. Similarly, osteotomy in conjunction with either simultaneous or staged cruciate ligament reconstruction appears to be beneficial in patients who have a combination of instability and pain from limb malalignment (Giffin and Fintan, 2007)

Infrapatellar soft-tissue realignment (Goldthwait) The lateral half of the patellar ligament is detached, threaded under the medial half and reattached more medially and distally. This operation is seldom used by itself but may be combined with suprapatellar realignment. Infrapatellar bony realignment (Elmslie-Trillat) The tibial tubercle is osteotomized and moved medially, thus improving the angle of pull on the patella. This procedure is only appropriate after closure of the proximal tibial physis; if growth is incomplete, damage to the physis may result in a progressive recurvatum deformity. NOTE: All these procedures can be combined with repair or tightening of the medial patello-femoral ligament. At the end of the operation it is essential to check that the patella moves smoothly to at least 60 degrees of knee flexion; excessive tightening or uneven tension may cause maltracking (and, occasionally, even medial subluxation!) of the patella. Patellectomy Occasionally the patello-femoral cartilage is so damaged that patellectomy is indicated, but this operation should be avoided if possible. There is a small risk that after patellectomy the patellar tendon may continue to dislocate and require realignment by the tibial tubercle transfer

RECURRENT SUBLUXATION Patellar dislocation is sometimes followed by recurrent subluxation rather than further episodes of complete displacement. This is the borderline between frank instability and maltracking of the patella (see below). OTHER TYPES OF NON-TRAUMATIC DISLOCATION Congenital dislocation, in which the patella is permanently displaced, is fortunately very rare. Reconstructive procedures, such as semitendinosus tenodesis, have been tried but the results are unpredictable. Habitual dislocation differs from recurrent dislocation in that the patella dislocates every time the knee is bent and reduces each time it is straightened. In longstanding cases the patella may be permanently dislocated. The probable cause is contracture of the quadriceps, which may be congenital or may result from repeated injections (usually antibiotics) into the muscle. Treatment requires lengthening of the quadriceps. Additionally a lateral capsular release and medial plication may be needed to hold the patella in the intercondylar groove

RUPTURE ABOVE THE PATELLA Rupture may occur in the belly of the rectus femoris. The patient is usually elderly, or on long-term corticosteroid treatment. The torn muscle retracts and forms a characteristic lump in the thigh. Function is usually good, so no treatment is required. Avulsion of the quadriceps tendon from the upper pole of the patella is seen in the same group of people. Sometimes it is bilateral. Operative repair is essential

RUPTURE BELOW THE PATELLA This occurs mainly in young people. The ligament may rupture or may be avulsed from the lower pole of the patella. Operative repair is necessary. Pain and tenderness in the middle portion of the patellar ligament may occur in athletes; CT or ultrasonography will reveal an abnormal area. If rest fails to provide relief the paratenon should be stripped (King et al., 1990). Partial rupture or avulsion sometimes leads to a traction tendinitis and calcification in the patellar ligament - the Sinding-Larsen Johansson syndrome (see below)

Treatment Both the haematologist and the orthopaedic surgeon should participate in treatment. The acute bleed may need aspiration, but only if this can be 'covered' by giving the appropriate clotting factor; otherwise it is better treated by splintage until the acute symptoms settle down. Flexion deformity must be prevented by gentle physiotherapy and intermittent splintage. If the joint is painful and eroded, operative treatment may be considered. However, although replacement arthroplasty is feasible, this should be done only after the most searching discussion with the patient, where all the risks are considered, and only if a full haematological service is available.

RUPTURES OF THE EXTENSOR APPARATUS Resisted extension of the knee may tear the extensor mechanism. The patient stumbles on a stair, catches his or her foot while walking or running, or may only be kicking a muddy football. In all these incidents, active knee extension is prevented by an obstacle. The precise location of the lesion varies with the patient's age. In the elderly the injury is usually above the patella; in middle life the patella fractures; in young adults the patellar ligament can rupture. In adolescents the upper tibial apophysis is occasionally avulsed; much more often it is merely 'strained'. Tendon rupture sometimes occurs with minimal strain; this is seen in patients with connective tissue disorders (e.g. SLE) and advanced rheumatoid disease, especially if they are also being treated with corticosteroids.

cause from anterior knee pain

Referred from hip 2. Patellofemoral disorders Patellar instability Patello-femoral overload Osteochondral injury Patello-femoral osteoarthritis 3. Knee joint disorders Osteochondritis dissecans Loose body in the joint Synovial chondromatosis Plica syndrome 4. Peri-articular disorders Patellar tendinitis Patellar ligament strain Bursitis Osgood-Schlatter disease

PATELLAR 'TENDINOPATHY' (SINDING- LARSEN JOHANSSON SYNDROME). This condition was described independently by Sinding- Larsen in 1921 and Johansson in 1922. Following a strain or partial rupture of the patellar ligament the patient (usually a young athletic individual) develops a traction 'tendinitis' characterised by pain and point tenderness at the lower pole of the patella. Sometimes, if the condition does not settle, calcification appears in the ligament (Medlar and Lyne, 1978). CT or ultrasonography may reveal the abnormal area in the ligament. A similar disorder has been described at the proximal pole of the patella. The condition is comparable to Osgood-Schlatter's disease and usually recovers spontaneously. If rest fails to provide relief, the abnormal area is removed and the paratenon stripped (King et al., 1990; Khan et al., 1998

SWELLINGS OF THE KNEE The knee is prone to a number of disorders which present essentially as 'swelling'; and, because it is such a large joint with a number of synovial recesses, the swelling is often painless until the tissues become tense. Conditions to be considered can be divided into four groups: swelling of the entire joint; swellings in front of the joint; swellings behind the joint; and bony swellings. ACUTE SWELLING OF THE ENTIRE JOINT POST-TRAUMATIC HAEMARTHROSIS Swelling immediately after injury means blood in the joint. The knee is very painful and it feels warm, tense and tender. Later there may be a 'doughy' feel. Movements are restricted. X-rays are essential to see if there is a fracture; if there is not, then suspect a tear of the anterior cruciate ligament. The joint should be aspirated under aseptic conditions. If a ligament injury is suspected, examination under anaesthesia is helpful and may indicate the need for operation; otherwise a crepe bandage is applied and the leg cradled in a back-splint. Quadriceps exercises are practised from the start. The patient may get up when comfortable, retaining the back-splint until muscle control returns.

Treatment A loose body causing symptoms should be removed unless the joint is severely osteoarthritic. This can usually be done through the arthroscope, but finding the loose body may be difficult; it may be concealed in a synovial pouch or sulcus and a small body may even slip under the edge of one of the menisci.

SYNOVIAL CHONDROMATOSIS This is a rare disorder in which the joint comes to contain multiple loose bodies, often in pearly clumps resembling sago ('snowstorm knee'). The usual explanation is that myriad tiny fronds undergo cartilage metaplasia at their tips; these tips break free and may ossify. It has, however, been suggested that chondrocytes may be cultured in the synovial fluid and that some of the products are then deposited onto previously normal synovium, so producing the familiar appearance (Kay et al., 1989). X-rays reveal multiple loose bodies; on arthrography they show as negative defects. Treatment The loose bodies should be removed arthroscopically. At the same time an attempt should be made to remove all abnormal synovium

CHRONIC SWELLING OF THE JOINT The diagnosis can usually be made on clinical and x-ray examination. The more elusive disorders should be fully investigated by joint aspiration, synovial fluid examination, arthroscopy and synovial biopsy. ARTHRITIS The commonest causes of chronic swelling are osteoarthritis and rheumatoid arthritis. Other signs, such as deformity, loss of movement or instability, may be present and x-ray examination will usually show characteristic features

SYNOVIAL DISORDERS Chronic swelling and synovial effusion without articular destruction should suggest conditions such as synovial chondromatosis and pigmented villonodular synovitis. The diagnosis will usually be obvious on arthroscopy and can be confirmed by synovial biopsy. The most important condition to exclude is tuberculosis. There has been a resurgence of cases during the last ten years and the condition should be seriously

case, those joints should be examined as well. Imaging X-ray The x-ray appearances are often unimpressive at the beginning, but a radionuclide scan may show increased activity on the medial side of the joint. Later the classic radiographic features of osteonecrosis appear (see Chapter 6). On the femoral side, it is always the dome of the condyle that is affected, unlike the picture in osteochondritis dissecans. Magnetic resonance imaging MRI enhances the ability to visualize bone marrow and to separate necrotic from viable areas with a high level of specificity. It shows the area of reactive bone surrounding the osteonecrotic lesion and can demonstrate the integrity of the overlying cortical shell of bone and articular cartilage. It is also helpful in determining prognosis concerning the natural course of the condition.

Special investigations Once the diagnosis is confirmed, investigations should be carried out to exclude generalized disorders known to be associated with osteonecrosis (see Chapter 6).Differential diagnosis Osteonecrosis of the knee should be distinguished from osteochondritis dissecans, though in truth the two conditions are closely related; however, the age group, aetiology, site of the lesion and prognosis are different and these factors may influence treatment. Other conditions that have a sudden, painful onset and tenderness at the joint line are fracture of an osteoarthritic osteophyte, disruption of a degenerative meniscus, a stress fracture, pes anserinus bursitis and a local tendonitis. Prognosis Symptoms and signs may stabilize and the patient be left with no more than slight distortion of the articular surface; or one of the condyles may collapse, leading to osteoarthritis of the affected compartment. The clinical progress depends on the radiographic size of the lesion, the ratio of size of the lesion to the size of the condyle (>40 per cent carries a worse prognosis) and the stage of the lesion (Patel et al., 1998

CONTRAINDICATIONS Contraindications include severe general disability because of age or multiple joint disease, especially if associated with problems in the ipsilateral hip or ankle; amputation or knee fusion of the opposite limb; and persistent non-union of a peri-articular fracture or massive peri-articular bone loss. Finally, patient reluctance may be an important factor. A short period in a plaster cylinder before operation may convince the patient that a rigidly stiff leg is better than a painful and unstable knee

TECHNIQUE A vertical midline incision is used. If the operation is for tuberculosis the diseased synovium is excised; otherwise it is disregarded. The posterior vessels and nerves are protected and the ends of the tibia and femur removed by means of straight saw cuts, aiming to end with 15 degrees of flexion and 7 degrees of valgus as the position of fusion. Charnley's method, using thick Steinman pins inserted parallel through the distal femur and proximal tibia, and connecting these with compression clamps, was for many years the standard method. Nowadays, multiplanar external fixation is used, or if the joint is not infected, a long intramedullary nail which may be unlocked or locked

PRINCIPLES OF KNEE OPERATIONS ARTHROSCOPY Arthroscopy is useful: (1) to establish or refine the accuracy of diagnosis; (2) to help in deciding whether to operate, and (3) to perform certain operative procedures. Arthroscopy is not a substitute for clinical examination; a detailed history and meticulous assessment of the physical signs are indispensable preliminaries and remain the sheet anchor of diagnosis.

TECHNIQUE Full asepsis in an operating theatre is essential. The patient is anaesthetized (though local anaesthesia may suffice for short procedures) and a thigh tourniquet applied. Through a tiny incision, a trocar and cannula is introduced; sometimes, saline is injected to distend the joint before it is punctured. Entry into the joint is confirmed when saline flows easily into the joint or, if the joint was distended previously, by the outflow when the trocar is withdrawn. A fibreoptic viewer, light source and irrigation system are attached; a small television camera and monitor make it much easier for the operator to concentrate on manipulating the instruments with both hands ('triangulation'). All compartments of the joint are now systematically inspected; with special instruments and, if necessary, through multiple portals, biopsy, partial meniscectomy, patellar shaving, removal of loose bodies, synovectomy, ligament replacement and many other procedures are possible. Before withdrawing the instrument, saline is squeezed out. A firm bandage is applied; the arthroscopic portals are often small enough not to require sutures. Postoperative recovery is remarkably rapid

OSGOOD-SCHLATTER DISEASE ('APOPHYSITIS' OF THE TIBIAL TUBERCLE) In this common disorder of adolescence the tibial tubercle becomes painful and 'swollen'. Although often called osteochondritis or apophysitis, it is nothing more than a traction injury of the apophysis into which part of the patellar tendon is inserted (the remainder is inserted on each side of the apophysis and prevents complete separation). There is no history of injury and sometimes the condition is bilateral. A young adolescent complains of pain after activity, and of a lump. The lump is tender and its situation over the tibial tuberosity is diagnostic. Sometimes active extension of the knee against resistance is painful and x-rays may reveal fragmentation of the apophysis. Spontaneous recovery is usual but takes time, and it is wise to restrict such activities as cycling, jumping and soccer. Occasionally, symptoms persist and, if patience or wearing a back-splint during the day are unavailing, a separate ossicle in the tendon is usually responsible; its removal is then worthwhile.

TENDINITIS AND CALCIFICATION AROUND THE KNEE CALCIFICATION IN THE MEDIAL LIGAMENT Acute pain in the medial collateral ligament may be due to a soft calcific deposit among the fibres of the ligament. There may be a small, exquisitely tender lump in the line of the ligament. Pain is dramatically relieved by operative evacuation of the deposit. PELLEGRINI-STIEDA DISEASE X-rays sometimes show a plaque of bone lying next to the femoral condyle under the medial collateral ligament. Occasionally this is a source of pain. It is generally ascribed to ossification of a haematoma following a tear of the medial ligament, though a history of injury is not always forthcoming. Treatment is rarely needed.

In patients with clotting disorders, the knee is the most common site for acute bleeds. If the appropriate clotting factor is available, the joint should be aspirated and treated as for a traumatic haemarthrosis. If the factor is not available, aspiration is best avoided; the knee is splinted in slight flexion until the swelling subsides. ACUTE SEPTIC ARTHRITIS Acute pyogenic infection of the knee is not uncommon. The organism is usually Staphylococcus aureus, but in adults gonococcal infection is almost as common. The joint is swollen, painful and inflamed; the white cell count and ESR are elevated. Aspiration reveals pus in the joint; fluid should be sent for bacteriological investigation, including anaerobic culture. Treatment consists of systemic antibiotics and drainage of the joint - ideally by arthroscopy, with irrigation and complete synovectomy; if fluid reaccumulates, it can be aspirated through a wide-bore needle. As the inflammation subsides, movement is begun, but weightbearing is deferred for 4-6 weeks.

TRAUMATIC SYNOVITIS Injury stimulates a reactive synovitis; typically the swelling appears only after some hours, and subsides spontaneously over a period of days. There is inhibition of quadriceps action and the thigh wastes. The knee may need to be splinted for several days but movement should be encouraged and quadriceps exercise is essential. If the amount of fluid is considerable, its aspiration hastens muscle recovery. In addition, any internal injury will need treatment. ASEPTIC NON-TRAUMATIC SYNOVITIS Acute swelling, without a history of trauma or signs of infection, suggests gout or pseudogout. Aspiration will provide fluid which may look turbid, resembling pus, but it is sterile and microscopy (using polarized light) reveals the crystals. Treatment with anti-inflammatory drugs is usually effective.

KNEE REPLACEMENT INDICATIONS The main indication for knee replacement is pain, especially when this is combined with deformity and instability. Most replacements are performed for rheumatoid arthritis or osteoarthritis

TYPES OF OPERATION Partial replacement The role of unicompartmental replacement has yet to be firmly established. Early results for medial compartment osteoarthritis were promising but longer-term studies have highlighted the need for meticulous and exacting surgical technique to avoid high revision rates. Following a successful operation, relief of pain and restoration of function can be impressive, but for the present it is reserved for older patients; tibial and femoral osteotomies are used in the younger population.

compared on the two sides. Internal and external rotation, though normally no more than about 10 degrees, should also be assessed. The patient's hip and knee are flexed to 90 degrees; one hand steadies and feels the knee, the other rotates the foot. Crepitus during movement may be felt with a hand placed on the front of the knee. It usually signifies patello-femoral roughness. Movement with compartmental loading is a useful test for localizing the site of joint pain; the medial or lateral compartment of the knee can be loaded separately by applying varus or valgus stress during flexion and noting which manoeuvre is more painful

Tests for intra-articular fluid Cross fluctuation This test is applicable only if there is a large effusion. The left hand compresses and empties the suprapatellar pouch while the right hand straddles the front of the joint below the patella; by squeezing with each hand alternately, a fluid impulse is transmitted across the joint

Complex ligament injuries When only a collateral or cruciate ligament is damaged the diagnosis is relatively easy: the direction of unstable movement is either sideways or front-to-back. With combined injuries the direction of instability may be oblique or rotational. Special clinical tests have been developed to detect these abnormalities (see Chapter 30); the best known is the pivot shift test. The patient lies supine with the lower limb completely relaxed. The examiner lifts the leg with the knee held in full extension and the tibia internally rotated (the position of slight rotational subluxation). A valgus force is then applied to the lateral side of the joint as the knee is flexed; a sudden posterior movement of the tibia is seen and felt as the joint is fully re-located. The test is sometimes quite painful

Tests for meniscal injuries McMurray's test This classic test for a torn meniscus is seldom used now that the diagnosis can easily be made by MRI. However, advanced imaging is not always available and the clinical test has not been altogether discarded. The test is based on the fact that the loose meniscal tag can sometimes be trapped between the articular surfaces and then induced to snap free with a palpable and audible click. The knee is flexed as far as possible; one hand steadies the joint and the other rotates the leg medially and laterally while the knee is slowly extended. The test is repeated several times, with the knee stressed in valgus or varus, feeling and listening for the click. A positive test is helpful but not pathognomonic; a negative test does not exclude a tear. Thessaly test This test is based on a dynamic reproduction of load transmission in the knee joint under normal or trauma conditions. With the affected knee flexed to 20 degrees and the foot placed flat on the ground, the patient takes his or her full weight on that leg while being supported (for balance) by the examiner (Fig. 20.9). The patient is then instructed to twist his or her body to one side and then to the other three times (thus, with each turn, exerting a rotational force in the knee) while keeping the knee flexed at 20 degrees. Patients with meniscal tears experience medial or lateral joint line pain and may have a sense of locking. The test has shown a high diagnostic accuracy rate at the level of 95 per cent in detecting meniscal tears, with a low number of false positive and negative recordings (Karachalios et al., 2005).

The patellar tap Again the suprapatellar pouch is compressed with the left hand to squeeze any fluid from the pouch into the joint. With the other hand the patella is then tapped sharply backwards onto the femoral condyles. In a positive test the patella can be felt striking the femur and bouncing off again (a type of ballottement).

The bulge test This is a useful method of testing when there is very little fluid in the joint, though it takes some practice to get it right! After squeezing any fluid out of the suprapatellar pouch, the medial compartment is emptied by pressing on the inner aspect of the joint; that hand is then lifted away and the lateral side

LESIONS OF THE MENISCI The menisci have an important role in (1) improving articular congruency and increasing the stability of the knee, (2) controlling the complex rolling and gliding actions of the joint and (3) distributing load during movement. During weightbearing, at least 50 per cent of the contact stresses are taken by the menisci when the knee is loaded in extension, rising to almost 90 per cent with the knee in flexion. If the menisci are removed, articular stresses are markedly increased; even a partial meniscectomy of one-third of the width of the meniscus will produce a threefold increase in contact stress in that area.

The medial meniscus is much less mobile than the lateral, and it cannot as easily accommodate to abnormal stresses. This may be why meniscal lesions are more common on the medial side than on the lateral. Even in the absence of injury, there is gradual stiffening and degeneration of the menisci with age, so splits and tears are more likely in later life - particularly if there is any associated arthritis or chondrocalcinosis. In young people, meniscal tears are usually the result of trauma.

X-ray The anteroposterior x-ray must be obtained with the patient standing and bearing weight; only in this way can small degrees of articular cartilage thinning be revealed. The tibio-femoral joint space is diminished (often only in one compartment) and there is subchondral sclerosis. Osteophytes and subchondral cysts are usually present and sometimes there is soft-tissue calcification in the suprapatellar region or in the joint itself (chondrocalcinosis). If only the patello-femoral joint is affected, suspect a pyrophosphate arthropathy.

Treatment If symptoms are not severe, treatment is conservative. Joint loading is lessened by using a walking stick. Quadriceps exercises are important. Analgesics are

Imaging X-rays may reveal loose bodies in the knee, derived from old osteochondral fragments. A lateral view with the knee in slight flexion may show a high-riding patella and tangential views can be used to measure the sulcus angle and the congruence angle. MRI is helpful and may show signs of the previous patello-femoral soft-tissue disruption

Treatment If the patella is still dislocated, it is pushed back into place while the knee is gently extended. The only indications for immediate surgery are (1) inability to reduce the patella (e.g. with a rare 'intra-articular' dislocation), and (2) the presence of a large, displaced osteochondral fragment. A plaster cylinder or splint is applied and retained for 2-3 weeks; isometric quadriceps-strengthening exercises are encouraged and the patient is allowed to walk with the aid of crutches.

Diagnosis There is still controversy as to whether 'plica syndrome' constitutes a real and distinct clinical entity. In some quarters, however, it is regarded as a significant cause of anterior knee pain. It may closely resemble other conditions such as patellar overload or subluxation; indeed, the plica may become troublesome only when those other conditions are present. The diagnosis is often not made until arthroscopy is undertaken. The presence of a chondral lesion on the femoral condyle secondary to plica impingement confirms the diagnosis.

Treatment The first line of treatment is rest, anti-inflammatory drugs and adjustment of activities. If symptoms persist, the plica can be divided or excised by arthroscopy. TUBERCULOSIS Tuberculosis of the knee may appear at any age, but it is more common in children than in adults. Clinical features Early presentation Pain and limp are early symptoms; or the child may present with a swollen joint and a low-grade fever. The thigh muscles are wasted, thus accentuating the joint swelling. The knee feels warm and there is synovial thickening. Movements are restricted and often painful. The Mantoux test is positive and the erythrocyte sedimentation rate (ESR) may be increased. X-rays show marked osteoporosis and, in children, enlargement of the bony epiphyses. Unlike pyogenic arthritis, joint space narrowing is a late sign; this is

X-ray The proximal tibial epiphysis is flattened medially and the adjacent metaphysis is beak-shaped. The medial cortex of the proximal tibia appears thickened; this is an illusory effect produced by internal rotation of the tibia. The tibial epiphysis sometimes looks 'fragmented'; occasionally the femoral epiphysis also is affected. In the late stages a bony bar forms across the medial half of the tibial physis, preventing further growth on that side. The degree of proximal tibia vara can be quantified by measuring the metaphyseo-diaphyseal angle (see Fig. 20.16). In contrast to physiological bowing, abnormal alignment occurs in the proximal tibia and not in the joint.

Treatment Spontaneous resolution is rare and, once it is clear that the deformity is progressing, a corrective osteotomy should be performed, addressing both the varus and the rotational components. A preoperative (or peroperative) arthrogram, to outline the misshapen epiphysis, will help in planning the operation.

is sharply compressed - a distinct ripple is seen on the flattened medial surface as fluid is shunted across. The juxta-patellar hollow test Normally, when the knee is flexed, a hollow appears lateral to the patellar ligament and disappears with further flexion; if there is excess fluid, the hollow fills and disappears at a lesser angle of flexion (Mann et al., 1991). Compare this in the two knees. The patello-femoral joint The size, shape and position of the patella are noted. The bone is felt, first on its anterior surface and then

along its edges and at the attachments of the quadriceps tendon and the patellar ligament. Much of the posterior surface, too, is accessible to palpation if the patella is pushed first to one side and then to the other; tenderness suggests synovial irritation or articular cartilage softening. Moving the patella up and down while pressing it lightly against the femur (the 'friction test') causes painful grating if the central portion of the articular cartilage is damaged. Pressing the patella laterally with the thumb while flexing the knee slowly may induce anxiety and sharp resistance to further movement; this, the 'apprehension test', is diagnostic of recurrent patellar subluxation or dislocation.

SIGNS WITH THE PATIENT LYING SUPINE The knees are the most visible and accessible of all the large joints; with the legs lying side by side, features on one side can be constantly compared with those on the other. Look The first things that strike one are the position of the knee. Is it symmetrical with the normal side? Is it held in valgus or varus, incompletely extended, or hyperextended? Note also the presence of swelling, either of the joint as a whole or as lumps or bumps in localized areas. Wasting of the quadriceps is a sure sign of joint disorder. The visual impression can be checked by measuring the girth of the thigh at the same level (e.g. a fixed distance above the joint line or a hand's breadth above the patella) in each limb. Look more closely for signs of bruising, and for old scars or sinuses, signifying previous infection or operations.

both with the knee at rest and during movement. Always compare the symptomatic with the normal side. Feel As with all joints, palpation of the knee - if it is to be rewarding - demands a sound knowledge of the local anatomy. Start by running your hand down the length of the limb, feeling for changes in skin temperature and comparing the symptomatic with the normal side. There is normally a gradual decrease in skin temperature from proximal to distal. Increased warmth over the knee signifies increased vascularity, usually due to inflammation. The soft tissues and bony outlines are then palpated systematically, feeling for abnormal outlines and localized tenderness. This is easier if the joint is flexed and the examiner sits on the edge of the couch facing the knee. By placing both hands over the front of the

LOOSE BODIES The knee - relatively capacious, with large synovial folds - is a common haven for loose bodies. These may be produced by: (1) injury (a chip of bone or

cartilage); (2) osteochondritis dissecans (which may produce one or two fragments); (3) osteoarthritis (pieces of cartilage or osteophyte); (4) Charcot's disease (large osteocartilaginous bodies); and (5) synovial chondromatosis (cartilage metaplasia in the synovium, sometimes producing hundreds of loose bodies).

If the fragment is 'unstable', i.e. surrounded by a clear boundary with radiographic 'sclerosis' of the underlying bone, or showing MRI features of separation, treatment will depend on the size of the lesion. A small fragment should be removed by arthroscopy and the base drilled; the bed will eventually be covered by fibrocartilage, leaving only a small defect. A large fragment (say more than 1 cm in diameter) should be fixed in situ with pins or Herbert screws. In addition, it may help to drill the underlying sclerotic bone to promote union of the necrotic fragment. For drilling, the area is approached from a point some distance away, beyond the articular cartilage

distance away, beyond the articular cartilage. If the fragment is completely detached but in one piece and shown to fit nicely in its bed, the crater is cleaned and the floor drilled before replacing the loose fragment and fixing it with Herbert screws. If the fragment is in pieces or ill-shaped, it is best discarded; the crater is drilled and allowed to fill with fibrocartilage. In recent years attempts have been made to fill the residual defects by articular cartilage transplantation: either the insertion of osteochondral plugs harvested from another part of the knee or the application of sheets of cultured chondrocytes. This approach should still be regarded as in the 'experimental' stage. After any of the above operations the knee is held in a cast for 6 weeks; thereafter movement is encouraged but weightbearing is deferred until x-rays show signs of healing.

DEFORMITIES OF THE KNEE By the end of growth the knees are normally in 5-7 degrees of valgus. Any deviation from this may be regarded as 'deformity', though often it bothers no one - least of all the possessor of the knees. The three common deformities are bow leg (genu varum), knock knee (genu valgum) and hyperextension (genu recurvatum). BOW LEGS AND KNOCK KNEES IN CHILDREN Deformity is usually gauged from simple observation. Bilateral bow leg can be recorded by measuring the

distance between the knees with the child standing and the heels touching; it should be less than 6 cm. Similarly, knock knee can be estimated by measuring the distance between the medial malleoli when the knees are touching with the patellae facing forwards; it is usually less than 8 cm. Physiological bow legs and knock knees Bow legs in babies and knock knees in 4-year-olds are so common that they are considered to be normal stages of development. Other postural abnormalities such as 'pigeon toes' and flat feet may coexist but

Tests for stability Collateral ligaments The medial and lateral ligaments are tested by stressing the knee into valgus and varus: this is best done by tucking the patient's foot under your arm and holding the extended knee firmly with one hand on each side of the joint; the leg is then angulated alternately towards abduction and adduction. The test is performed at full extension and again at 30 degrees of flexion. There is normally some medio-lateral movement at 30 degrees, but if this is

excessive (compared to the normal side) it suggests a torn or stretched collateral ligament. Sideways movement in full extension is always abnormal; it may be due to either torn or stretched ligaments and capsule or loss of articular cartilage or bone, which allows the affected compartment to collapse.