chapter 8 joints

Elevation and Depression

Elevation means lifting a body part superiorly. For example, the scapulae are elevated when you shrug your shoulders. Moving the elevated part inferiorly is depression. During chewing, the mandible is alternately elevated and depressed.

Lyme Disease

an inflammatory disease caused by spirochete bacteria transmitted by the bite of ticks that live on mice and deer. It often results in joint pain and arthritis, especially in the knees, and is characterized by a skin rash, flu-like symptoms, and foggy thinking. If untreated, neurological disorders and irregular heartbeat may ensue. Antibiotic therapy is the usual treatment, and works best when initiated soon after the initial infection.

angular movements

angular movements - increase or decrease the angle between two bones. (flexion, extension, hyperextension, abduction, adduction, and circumduction.) ----------------------------------------- Flexion - is a bending movement, usually along the sagittal plane, that decreases the angle of the joint and brings the articulating bones closer together ex. Examples include bending the head forward on the chest and bending the body trunk or the knee from a straight to an angled position extension - the reverse of flexion and occurs at the same joints. involves movement along the sagittal plane that increases the angle between the articulating bones and typically straightens a flexed limb or body part. ex. straightening a flexed neck, body trunk, elbow, or knee Abduction - s movement of a limb away from the midline or median plane of the body, along the frontal plane. ex. Raising the arm or thigh laterally is an example of abduction (Figure 8.Se). For the fingers or toes, abduction means spreading them apart. Adduction - ("moving toward") is the opposite of abduction, so it is the movement of a limb toward the body midline or, in the case of the digits, to\vard the midline of the hand or foot. Circumduction - moving a limb so that it describes a cone in space The distal end of the limb moves in a circle, while the point of the cone (the shoulder or hip joint) is more or less stationary A pitcher winding up to throw a ball is actually circumducting his or her pitching arm. Because circumduction consists of flexion, abduction, extension, and adduction performed in succession, it is the quickest way to exercise the many muscles that move the hip and shoulder ball-and-socket joints. Rotation- turning of a bone around its own Jong axis. It is the only movement allowed between the first two cervical vertebrae and is common at the hip and shoulder joints. Rotation may be directed toward the midline or away from it. For example, in, medial rotation of the thigh, the femur's anterior surface moves toward the median plane of the body; lateral rotation is the opposite movement. special movements: Supination - turning backward Pronation - turning forward In pronation, the forearm rotates medially and the palm faces posteriorly or inferiorly. Pronation moves the distal end of the radius across the ulna so that the two bones form an X. This is the forearm's position when we are standing in a relaxed manner. Pronation is a much weaker movement than supination. A trick to help you keep these terms straight: A pro basketball player pronates his or her forearm to dribble the ball.

synovial joints

articulating bones separated by a fluid-filled joint cavity this fluid cavity permits movement, all synovial joints are freely moveable diarthrosis. nearly all joints of limbs - most joints of body - fall into this class ---------------------------------------------------- have 6 distinguishing features : 1) Articular cartilage - Glassy-smooth hyaline cartilage covers the opposing bone surfaces as articular cartilage. These thin ( l mm or less) but spongy cushions absorb compression placed on the joint and thereby keep the bone ends from being cn1shed. 2) joint (articular) cavity - The joint cavity is a feature that is unique to synovial joints. It contains a small an1ount of synovial fluid. The joint cavity is a potential space because it is normally almost nonexistent, but can expand if fluid accumulates (as happens during inflammation). 3) Articular capsule - The joint cavity is enclosed by a two-layered articular capsule, or joint capsule. The tough external fibrous layer is composed of dense irregular connective tissue that is continuous with the periostea of the articulating bones. It strengthens the joint so that the bones are not pulled apart. The inner layer of the joint capsule is a synovial membrane composed of loose connective tissue. Besides lining the fibrous layer inten1ally, it covers all internal joint surfaces that are not hyaline cartilage. The synovial membrane's function is to make synovial fluid. 4) Synovial fluid - A small amount of slippery synovial fluid occupies all free spaces within the joint capsule. This flu id is derived largely by filtration from blood flowing through the capillaries in the synovial membrane. Synovial fluid has a viscous, egg-white consistency (ovurn = egg) due to hyaluronic acid secreted by cells in the synovial membrane, but it thins and becomes Jess viscous during joint activity. Synovial flu id, which is also found within the articular cartilages, provides a slippery, weight-bearing film that reduces friction bet\veen the cartilages. Without this lubricant, rubbing would wear away joint surfaces and excessive friction could overheat and destroy the joint tissues. The synovial fluid is forced from the cartilages when a joint is compressed; then as pressure on the joint is relieved, synovial fluid seeps back into the articular cartilages like water into a sponge, ready to be squeezed out again the next time the joint is loaded (put under pressure). This process, called weeping lubrication, lubricates the free surfaces of the cartilages and nourishes their cells. (Remember, cartilage is avascular.) Synovial fluid also contains phagocytic cells that rid the joint cavity of microbes and cellular debris. 5) Reinforcing ligaments - Synovial joints are reinforced and strengthened by a number of bandlike ligaments. Most often, these are capsular Iigarnents, which are thickened parts of the fibrous layer. In other cases, they remain distinct and are found outside the capsule (as extracapsular ligaments) or deep to it (as intracapsular ligaments). Since intracapsular ligaments are covered with synovial membrane, they do not actually lie within the joint cavity. People said to be double-jointed amaze the rest of us by placing both heels behind their neck. However, they have the normal number of joints. It's just that their joint capsules and ligaments are more stretchy and loose than average. 6) Nerves and blood vessels - Synovial joints are richly supplied with sensory nerve fibers that innervate the capsule. Some of these fibers detect pain, as anyone who has suffered joint injury is aware, but most monitor joint position and stretch. Monitoring joint stretch is one of several ways the nervous system senses our posture and body movements (seep. 493). Synovial joints are also richly supplied with blood vessels, most of which supply the synovial membrane. TI1ere, extensive capillary beds produce the blood filtrate that is the basis of synovial fluid. Besides the basic components just described, certain synovial joints have other structural features. Some, such as the hip and knee joints, have cushioning fatty pads between the fibrous layer and the synovial membrane or bone. Others have discs or wedges of fibrocartilage separating the articular surfaces. Where present, these articular discs, or ,menisci (me-nis'ki;"crescents"), extend inward from the articular capsule and partially or completely divide the synovial cavity in two (see the menisci of the knee in Figure 8.11 b, e, and f). Articular discs improve the fit between articulating bone ends, making the joint more stable and minimizing wear and tear on the joint surfaces. Besides the knees, articular discs occur in the jaw and a few other joints (see notations in the Structural Type column in Table 8.2).

which structure most directly acts to reduce friction during joint movement?

bursae

Bursitis a nd Tendonitis

bursitis: inflammation of a bursa and is usually caused by a blow or friction. Falling on one's knee may result in a painful bursitis of the prepatellar bursa, known as house111aid's knee or water on the knee. Prolonged leaning on one's elbows may damage the bursa close to the olecranon, producing student's elbow, or olecrawn bursitis. treatment: severe case treated by injecting anti-inflammatory drugs into the bursa. If excessive flu id accumulates, removing some fluid by needle aspiration may relieve the pressure. tendonitis: is inflammation of tendon sheaths, typically caused by overuse. Its symptoms (pain and swelling) and treatment (rest, ice, and anti-inflammatory drugs) mirror those of bursitis.

Arthritis

describes over I 00 different types of inflammatory or degenerative diseases that damage the joints. forms, arthritis is the most widespread crippling disease in North America. One in five of us suffers its ravages. To a greater or lesser degree, all forms of arthritis have the same initial symptoms: pain, stiffness, and swelling of the joint. Acute forms of arthritis usually result from bacterial invasion and are treated with antibiotics. Chronic forms of arthritis include osteoarthritis, rheumatoid arthritis, and gouty arthritis.

articular surfaces

shape of surface determine possible movement at joint only play a minor role in joint stability Many joints have shallow sockets or noncomplementary articulating surfaces ("misfits") that actually hinder joint stability. But when articular surfaces are large and fit snugly together, or when the socket is deep, stability is vastly improved. ' ex The ball and deep socket of the hip joint provide the best example of a joint made extremely stable by the shape of its articular surfaces.

Inversion and eversion

special movements of the foot. In inversion, the sole of the foot turns medially. In eversion, the sole faces laterally.

Five examples illustrate the diversity of synovial joints

temporomandibular (jaw), shoulder, elbow, hip, and knee joints. all have 6 distinguishing characteristics of synovial joints.

cartilaginous joints

the articulating bones are united by cartilage. Like fibrous joints, they lack a joint cavity and are not highly movable. The two types of cartilaginous joints are: synchondroses - bar or plate of hyaline cartilage unites the bones at a synchondrosis (sin"kon-dro 'sis; "junction of cartilage" Virtually all synchondroses are synarthrotic (immovable). most common ex are epiphyseal plates in long bones of children (epiphyseal plates - temporary joints, eventually become synostoses.) Another example of a synchondrosis is the immovable joint between the costal cartilage of the first rib and the manubrium of the sternum ----------------------------------------------------- symphyses- A joint where fibrocartilage unites the bones is a symphysis Since fibrocartilage is compressible and resilient, it acts as a shock absorber and permits a limited amount of movement at the joint. Even though fibrocartilage is the main element of a symphysis, hyaline cartilage is also present in the form of articular cartilages on the bony surfaces. are amphiarthrotic joints designed for strength with flexibility. Examples include the intervertebral joints and the pubic symphysis of the pelvis

3 joint functional classifications

the functional classification is based on the amount of movement allowed at the joint. synarthroses - (sin"ar-thro'sez; syn = together, arthro = joint), which are immovable joints (Immovable and slightly movable joints are largely restricted to the axial skeleton.)the less movable the joint, the more stable it is likely to be amphiarthroses - (am"fe-ar-thro' sez; amphi = on both sides), slightly movable joints (Immovable and slightly movable joints are largely restricted to the axial skeleton.)the less movable the joint, the more stable it is likely to be diarthroses - (di"ar-thro' sez; dia = through. apart), or freely movable joints. (Freely rnovable joints predominate in the appendicular skeleton (limbs).) In general, fibrous joints are immovable, and synovial joints are freely movable. However, cartilaginous joints have both rigid and slightly movable examples

movements at which of the following joints result in pronation and supination?

radius - ulna

hip joint (coxal joint)

-strong ball and socket diarthrosis -wide range of motion (not as wide as shoulder range) -ball and socket joint -movement in all planes but limited by joints strong ligaments + deep socket. -formed by articulation of spherical head of femur w deeply cupped acetabulum of hip bone. -The depth of the acetabulum is enhanced by a circular rim of fibrocartilage called acetabular labrum. . Because the diameter of the labrum is smaller than that of the head of the femur, the femur cannot easily slip out of the socket, and hip dislocations are rare. The thick articular capsule extends from the rim of the acetabulum to the neck of the femur and completely encloses the joint. Several strong ligaments reinforce the capsule of the hip joint. These include: • The iliofemoral ligament (il"e-o-fem'o-ral), a strong V-shaped ligament ai1teriorly • The pubofemoral ligament (pu"bo-fem'o-ral), a triangular thickening of the inferior part of the capsule • The ischiofemoral ligament (is"ke-o-fem'o-ral), a spiraling posterior ligament (These ligaments are arranged in such a way that they "screw" the femur head into the acetabulum when a person stands up straight, thereby providing stability.) The ligament of the head of the femur, also called the ligamentum teres, is a flat intracapsular band that runs from the femur head to the lower lip of the acetabulum (this ligament is slack during most hip movements, not important in stabilizing joint) (mechanical function is actually unclear however it contains artery which helps supply head of femur) (if this artery is damaged could lead to arthritis) stability + strength comes from muscle tendons that cross the joint and bulky hip and thigh muscles that surround it. and mostly from deep socket that securely encloses femoral head to strong capsular ligaments.

dislocation (luxation)

A dislocation (luxation) occurs when bones are forced out of alignment. It is usually accompanied by sprains, inflammation,

Cartilage Tears

Although most cartilage injuries involve tearing of the knee menisci, tears and overuse damage to the articular cartilages of other joints is becoming increasingly common in young athletes. from overdue in exercise Cartilage tears typically occur when a meniscus is subjected to compression and shear stress at the same time. Cartilage is avascular and it rarely can obtain sufficient nourishment to repair itself, so it usually stays torn. cartilage fragments can cause joint to lock or bind]] sports physicians recommend damaged cartilage be removed via arthroscopic surgery.

Shoulder (Glenohumeral) Joint

Ball-and-socket joint Head of humerus with glenoid cavity of scapula Most freely moving joint in body Stability sacrificed The large hemispherical head of the humerus fits in the small, shallow glenoid cavity of the scapula, like a golf ball sitting on a tee Although the glenoid cavity is slightly deepened by a rim of fibrocartilage, the glenoid labrum (labrum = lip), it is only about one-third the size of the humeral head and contributes little to joint stability The articular capsule enclosing the joint cavity is very thin and loose, this contributes to freedom of movement. The few ligaments reinforcing the shoulder joint are located primarily on its anterior aspect . • The superiorly located coracohu1ner al ligament (kor'al1-ko-hu'mer-ul) provides the only strong thickening of the capsule and helps support the weight of the upper limb • Three glenohumeral ligaments (gle"no-hu' mer-ul) strengthen the front of the capsule somewhat but are weak and may even be absent muscle tendons that cross shoulder joint make joint better stability "superstabilizer" is the tendon of the Jong head of the biceps brachii muscle of the arm (This tendon attaches to the superior margin of the glenoid labrum, travels through the joint cavity, and then runs within the intertubercular sulcus of the humerus. It secures the head of the humerus against the glenoid cavity.) Four other tendons (and the associated muscles) make up the rotator cuff. This cuff encircles the shoulder joint and blends with the articular capsule. The four muscles of the rotator cuff are the subscapularis, supraspinatus, infraspinatus, and teres minor.. The rotator cuff can be severely stretched when the arm is vigorously circumducted; this is a common injury of baseball pitchers. HOMEOSTATIC IMBALANCE: One price of mobility in the shoulder is that shoulder dislocations are common injuries_-. Because the structures reinforcing this joint are weakest anteriorly and inferiorly, the head of the humerus easily dislocates forward and downward. The glenoid cavity provides poor support when the humerus is rotated laterally and abducted, as when a football player uses the arm to tackle an opponent or a baseball fielder hits the ground diving for a ball. These situations may cause shoulder dislocations, as do blows to the top and back of the shoulder.

Movements Allowed by Synovial Joints

Every skeletal muscle of the body is attached to bone or other connective tissue structures at no fewer than 2 points. The muscle's origin is attached to the immovable (or Jess movable) bone. Its other end, the insertion, is attached to the movable bone. body movement = when muscles contract across joints and insertion moves toward origin The movements can be described in directional terms relative to the lines, or axes, around which the body part moves and the planes of space along which the movement occurs, that is, along the transverse, frontal, or sagittal plane. Range of motion allowed by synovial joints varies: nonaxial movement (gliding movements only) uniaxial 1novement (movement in one plane) biaxial 1novement (movement in two planes) multiaxial ,movement (movement in or around all three planes of space and axes) rom varies a ton in ppl. --------------------------------------- 3 types of movement: gliding - when one flat or nearly flat bone surface glides or slips over another without appreciable angulation or rotation location: Gliding occurs at the intercarpal and intertarsal joints, and between the flat articular processes of the vertebrae angular movements - increase or decrease the angle between two bones. (flexion, extension, hyperextension, abduction, adduction, and circumduction.) may occur in any plane of the body and include flex ion, extension, hyperextension, abduction, adduction, and circumduction rotation -

Muscle Tone

For most joints, the muscle tendons that cross the joint are the most important stabilizing factor. These tendons are kept under tension by the tone of their muscles. (Muscle tone is defined as low levels of contractile activity in relaxed muscles that keep the muscles healthy and ready to react to stimulation.) Muscle tone is extremely important in reinforcing the shoulder and knee joints and the arches of the foot.

Common Joint Injuries

For most of us, sprains and dislocations are the most common trauma-induced joint injuries. However, cartilage injuries, which are common among athletes, are the most problematic.

fibrous joints

In fibrous joints, the bones are joined by the collagen fibers of connective tissue. No joint cavity is present. The amount of movement allowed depends on the length of the connective tissue fibers. Most fibrous joints are immovable, although a few are slightly movable. The three types of fibrous joints are: sutures- literally "seams;• occur only bel\veen bones of the skull. The wavy articulating bone edges interlock, and teeth embedded in sockets as if hammered in. The fibrous connection in this case is the short periodontal ligament syndesmoses- gomphoses-

Inflammatory and Degenerative Conditions

Inflammatory conditions that affect joints include bursitis and tendonitis, various forms of arthritis, and Lyme disease.

joints are easily damaged by injury, inflammation, and degeneration

Joint pain and malfunction can be caused by a number of factors besides traumatic injury, including inflammatory conditions and degenerative processes due to friction and wear.

Protraction and Retraction

Nonangular anterior and posterior movements in a transverse plane are called protraction and retraction, respectively. The mandible is protracted when you jut out your jaw and retracted when you bring it back.

Bursae (bursa) and Tendon Sheaths

Often found closely associated with synovial joints Essentially bags of lubricant, they act as "ball bearings" to reduce friction between adjacent structures during joint activity. ----------------------------------------------------- Bursae (ber' se; "purse") are flattened fibrous sacs lined with synovial membrane and containing a thin film of synovial fluid. They occur where ligaments, muscles, skin, tendons, or bones rub together. ---------------------------------------------------------- A tendon sheath is essentially an elongated bursa that wraps completely around a tendon subjected to friction, like a bun around a hot dog. They are common where several tendons are crowded together within narrow canals (in the wrist, for example).

ligaments

The capsules and ligaments of synovial joints unite the bones and prevent excessive or undesirable motion the more ligaments a joint has, the stronger it is. However,,,,,,, when other stabilizing factors are inadequate, undue tension is placed on the ligaments and they stretch. Stretched ligaments stay stretched, like taffy, and a ligament can stretch only about 6% of its length before it snaps. Thus, when ligaments are the major means of bracing a joint, the joint is not very stable.

Opposition

The saddle joint between metacarpal I and the trapezium allows a movement called opposition of the thumb. This movement is the action taken when you touch your thumb to the tips of the other fingers on the same hand. It is opposition that makes the human hand such a fine tool for grasping and manipulating objects.

Dorsiflexion and Plantar Flexion of the Foot

The up-and down movements of the foot at the ankle are given more specific names (Figure 8.6b). Lifting the foot so that its superior surface approaches the shin is dorsiflexion (corresponds to wrist extension), whereas depressing the foot (pointing the toes) is plantar flexion (corresponds to wrist flex ion).

Gouty Arthritis

Uric acid, a normal waste product of nucleic acid metabolism, is ordinarily excreted in urine without ai1y problen1s. However, when blood levels of uric acid rise excessively (due to its excessive production or slow excretion), it may be deposited as needle-shaped urate crystals in the soft tissues of joints. An inflammatory response follows, leading to an agonizingly painful attack of gouty arthritis (gow'te), or gout. The initial attack typically affects one joint, often at the base of the great toe.

which is a unique feature of synovial joints?

a fluid filled cavity

Temporomandibular Joint or (jaw joint) (TMJ)

a modified hinge joint lies just anterior to the ear. At this joint, the condylar process of the mandible articulates with the inferior surface of the squamous part of the temporal bone(~ p. 208). The mandible's condylar process is egg shaped, whereas the articular surface of the temporal bone has a more complex shape. it forms the concave mandibular fossa; anteriorly it forms a dense knob called the articular tubercle. The lateral aspect of the loose articular capsule that encloses the joint is thickened into a lateral ligament. Within the capsule, an articular disc divides the synovial cavity into superior and inferior compartments two types of movement: . First, the concave inferior disc surface receives the condylar process of the mru1dible and allows the familiar hinge like movement of depressing and elevating the mandible while opening and closing the mouth. Second, the superior disc surface glides anteriorly along with the condylar process when the mouth is opened wide. This anterior movement braces the condylar process against the articular tubercle, so that the mandible is not forced through the thin roof of the mandibular fossa when one bites hard foods such as nuts or hard candies. The superior compartment also allows this joint to glide from side to side. As the posterior teeth are drawn into occlusion during grinding, the mandible moves with a side-to-side movement called lateral excursion. This lateral jaw movement is unique to mammals and it is readily apparent in horses and cows as they chew. -------------------------------------------- HOMEOSTATIC IMBALANCE : Dislocations of the TMJ occur more readily than any other joint dislocation because of the shallow socket in the joint. Even a deep yawn can dislocate it. This joint almost always dislocates anteriorly, the condylar process of the mandible ending up in a skull region called the infratemporal fossa' In such cases, the mouth remains wide open. To realign a dislocated TMJ, the physician places his or her thumbs in the patient's mouth between the lower molars and the cheeks, and then pushes the mandible inferiorly and posteriorly. At least 5% of Americans suffer from painful TMJ disorders, the most common symptoms of which are pain in the ear and face, tenderness of the jaw muscles, popping sounds when the mouth opens, and joint stiffness. Usually caused by painful spasms of the chewing muscles, TMJ disorders often afflict people who grind their teeth; however, it can also result from jaw trauma, or from poor occlusion of the teeth. treatment focuses on jaw relaxation muscle relaxant drugs, heat or cold, stress reduction.

Rheumatoid Arthritis Rheumatoid arthritis (RA)

chronic inflammatory disorder usually arises between the ages of 30 and 50, but can occur at any age. It affects three times as many women as men. While not as common as osteoarthritis, rheumatoid arthritis affects millions, about I% of all people. early stage: joint tenderness, stiffness Many joints, particularly the small joints of the fingers, wrists, ankles, and feet, are afflicted at the same time and bilaterally. For example, if the right elbow is affected, most likely the left elbow is also affected. The course of RA is variable and marked by flare-ups (exacerbations) and remissions (rhewnat = susceptible to change). Along with pain ai1d swelling, its manifestations may include anemia, osteoporosis, muscle weakness, and cardiovascular problems. RA is an autoimmune disease, initial trigger is unknown, but various bacteria and viruses have been suspected.

which angular movements result from a combination of the other three choices?

circumduction

which of the following provides significant stability to the articulation between the femur and tibia?

cruciate ligaments

structural classification of joints - 3

fibrous- connected by fiberous tissue cartilaginous- the bones are connected by cartilage synovial- Only synovial joints have a joint cavity. have a fluid-filled joint cavity The structural classification focuses on the material binding the bones together and whether or not a joint cavity is present.

which of the following synovial joint types would allow for flexion and extension movements only?

hinge joint

factors of stability of synovial joints

joints particularly synovial joints r weakest parts of the skeleton their structure resists various forces, such as crushing or tearing, that threaten to force them out of alignment bc they are constantly stretched and compressed they need to be stabilized to they don't dislocate, stability depends on : • The shapes of the articular surfaces • The number and positioning of ligaments • Muscle tone

Knee Joint

largest and most complex joint in the body single joint cavity BUT knee consists of three joints in one: intermediate one between patella + lower end femur (femoropatellar joint) and lateral and medial joints (collectively known as the tibiofe1noral joint) between the femoral condyles above and the C-shaped 1ne11isci, or se1nilu11ar cartilages, of the tibia below. deepens shallow tibial articular surfaces, menisci also helps prevent side to side rocking of femur on tibia and absorb sock to knee joint. However, the menisci are attached only at their outer margins and are frequently tom free. tibiofemoral joint acts primarily as a hinge, permitting flexion and extension. However, structurally it is a bicondylar joint. Some rotation is possible when the knee is partly flexed, and when the knee is extending. But when the knee is fully extended, side-to-side movements and rotation are strongly resisted by ligaments and the menisci. The femoropatellar joint is a plane joint, and the patella glides across the distal end of the femur during knee flexion. joint cavity is partially enclosed by a capsule. (thin articular capsule present only on sides and posterior aspects of knee where it covers the bulk of the femoral and tibial condyles.) Anteriorly, where the capsule is absent, three broad ligaments run from the patella to the tibia below. These are the patellar ligament flanked by the medial and lateral patellar retinacula (ret"i-nak'u-Jah; "retainers"), which merge imperceptibly into the articular capsule on each side. The patellar ligament and retinacula are actually continuations of the tendon of the bulky quadriceps muscle of the anterior thigh. Physicians tap the patellar ligament to test the knee-jerk reflex. synovial cavity of knee joint: complicated shape, several extensions that lead into "dead ends". at least 12 bursae associated with joint. All three types of joint ligaments (extracapsular, capsular, and intracapsular) stabilize and strengthen the capsule of the knee joint. All of the capsular and extracapsular ligaments act to prevent hyperextension of the knee and are stretched tight when the knee is extended. These include the following: • The extracapsular fibular and tibial collateral ligaments are also critical in preventing lateral or medial rotation when the knee is extended. The broad, flat tibial collateral ligament runs from the medial epicondyle of the femur to the medial condyle of the tibial shaft below and is fused to the n1edial meniscus • The oblique popliteal liga1nent (pop"li-te'al) is actually part of the tendon of the semimembranosus muscle that fuses with the joint capsule and helps stabilize the posterior aspect of the knee joint • The arcuate popliteal liga1nent arcs superiorly from the head of the fibula over the popliteus muscle and reinforces the joint capsule posteriorly . ------------- The knee's intracapsular ligaments are called cruciate liga1nents (kroo' she-at) because they cross each other, forming an X (cruci = cross) in the notch between the femoral condyles. (act as restraining straps, prevents anteior-posteior displacement of articular surfaces & secure articulating bones when we stand) Although these ligaments are in the joint capsule, they are outside the synovial cavity, and synovial membrane nearly covers their surfaces. Note that the two cruciate ligaments both run superiorly to the femur and are named for their tibial attachment site. anterior cruciate ligament attaches to the anterior intercondylar area of the tibia. from there, passes posteriorly, laterally, + upward to attach to femur on medial side of later condyle. this ligament prevents forward sliding of tibia on femur + checks hyperextension of knee. somewhat lax when knee is flexed, and taut when knee is extended. The stronger posterior cruciate ligament is attached to the posterior intercondylar area of the tibia and passes anteriorly, medially, and superiorly to attach to the femur on the lateral side of the medial condyle. This ligament prevents backward displacement of the tibia or forward sliding of the femur. The knee capsule is heavily reinforced by muscle tendons. Most important are the strong tendons of the quadriceps muscles of the anterior thigh and the tendon of the semimembranosus muscle posteriorly. The greater the strength and tone of these muscles, the less the chance of knee injury. knees have built-in locking device provides steady support for bod in standing. As we begin to stand up, the wheel-shaped femoral condyles roll like ball bearings across the tibial condyles and the flexed leg begins to extend at the knee. Because the lateral femoral condyle stops rolling before the medial condyle stops, the femur spins (rotates) medially on the tibia, until the cruciate and collateral ligaments of the knee are twisted and taut and the menisci are compressed. The tension in the ligaments effectively Jocks the joint into a rigid structure that cannot be flexed again until it is unlocked. This unlocking is accomplished by the popliteus muscle.. It rotates the femur laterally on the tibia, causing the ligaments to become untwisted and slack. HOMEOSTATIC IMBALANCE Of all body joints, the knees are most susceptible to sports inj uries because of their high reliance on nonarticular factors for stability and the fact that they carry the body's weight. The knee can absorb a vertical force equal to nearly seven times body weight. However, it is very vulnerable to horizontal blows, such as those that occur during blocking and tackling in football and in hockey. When thinking of co,nmon knee injuries, remember the 3 Cs: • Collateral ligaments • Cruciate ligaments • Cartilages (menisci) Most dangerous are Lateral blows to the extended knee. These forces tear the tibial collateral ligament and the medial meniscus attached to it, as well as the anterior cruciate ligament (ACL) (Figure 8.12). It is estimated that 50% of all professional football players have serious knee injuries during their careers. Although Jess devastating than the injury just described, injuries that affect only the anterior cruciate ligament are becoming more common, particularly as women's sports become more vigorous and competitive. Most ACL injuries occur when a runner changes direction quickly, t\visting a hyperextended knee. A torn ACL heals poorly, so repair usually requires a graft taken from either the patellar ligament, the hamstring tendon, or the calcaneal tendon.

Osteoarthritis Osteoarthritis (OA)

most common chronic arthritis. A chronic degenerative condition, OA is often called "wear-and-tear arthritis." OA is most prevalent in the aged and is probably related to the normal aging process (although it is seen occasionally in younger people and some forms have a genetic basis). More women than men are affected, and nearly all of us will develop this condition by the age of 80. normal joint use prompts the release of (metalloproteinase) enzymes that break down articular cartilage, especially its collagen fibrils. In healthy individuals, this damaged cartilage is eventually replaced, but in people with OA, more cartilage is destroyed than replaced. specific cause unknown, OA may reflect the cumulative effects of years of compression and abrasion acting at joint surfaces, causing excessive amounts of the cartilage-destroying enzymes to be released. result: softened, roughened, pitted, eroded articular cartilages. As the disease progresses, the exposed bone tissue thickens and forms bony spurs (osteophytes) that enlarge the bone ends and may restrict joint movement. The course of osteoarthritis is usually slow and irreversible. In many cases, its symptoms are controllable with a mild pain reliever like aspirin or acetaminophen, along with ,moderate activity to keep the joints mobile.

types of synovial joints

plane, hinge, pivot, condyloid, saddle, ball and socket

Sprains

the ligaments reinforcing a joint are stretched or torn. Common sites of sprains are the ankle, the knee, and the lumbar region of the spine. Partially ton1 ligaments will repair themselves, but they heal slowly because ligaments are so poorly vascularized. Sprains tend to be painful and immobilizing. When ligaments are completely torn, there are three options: • The tom ends of the ligament can be sewn together. This is difficult because trying to sew the hundreds of fibrous strands of a ligament together is like trying to sew two hairbrushes together. • Certain ligaments, like the anterior cruciate ligament, are best repaired by replacing them with grafts. For example, a piece of tendon from a muscle can be attached to the articulating bones. • For many ligaments, such as the knee's medial collateral ligament, it tun1s out that time and immobilization are just as effective as any surgical option.

Elbow Joint

the most prominent of the upper limb joints is the elbow provides a stable and smoothly operating hinge that allows flexion and extension only Within the joint, both the radius and ulna articulate with the condyles of the humerus, but it is the close gripping of the trochlea by the ulna's trochlear notch that forms the "hinge" and stabilizes this joint. A relatively lax articular capsule extends inferiorly from the humerus to the ulna and radius, and to the anular ligament (an'u-Jar) encircling the head of the radius. Anteriorly and posteriorly, the articular capsule is thin and allows substantial freedom for elbow flexion and extension. However, side-to-side movements are restricted by two strong capsular ligaments: the ulnar collateral ligament medially, and he radial collateral ligament, a triangular ligan1ent on the lateral side (Figure 8.9b, c, and d). Additionally, tendons of several arm muscles, such as the biceps and triceps, cross the elbow joint and provide security. The radius is a passive "onlooker" in the angular elbow movements. However, its head rotates within the anular ligament during supination and pronation of the forearm.