Kinesiology of pelvis and hip

Hip adductors as internal rotators

The adductor muscles as secondary internal rotators of the hip. (A) If the femur is straight, then the adductors attaching to the posterior femur along the linea aspera will tend to be external rotators. However because of the anterior bowing of the femoral shaft, a large segment of the linea aspera (short red line) runs anterior to the longitudinal axis of rotation (blue rod). (B) A superior view of the right hip shows the horizontal line of force of the adductor longus. The muscle causes an internal rotation torque by producing a force that passes anterior to the axis of rotation (small blue circle at femoral head). The moment arm used by the adductor longus is indicated by the thick dark line. The oval set of dashed black lines represents the outline of the midshaft of the femur at the region of the distal attachment of the adductor longus.

What is the role of hamstrings in forward lean?

(A) Slight forward lean of the upper body displaces the body weight force slightly anterior to the medial-lateral axis of rotation at the hip, controlled by minimal gluteus maximus activation. (B) A more significant forward lean displaces the body weight force even farther anteriorly. The greater flexion of the hips rotates the ischial tuberosities posteriorly, thereby increasing the hip extension moment arm of the hamstrings. (and decreasing the moment arm of the gluteus maximus) The taut line (with arrowhead within the stretched hamstring muscles) indicates the increased passive tension. In both (A) and (B), the relative demands placed on the muscles are shown by relative shades of red. The graph shows the lengths of hip extension moment arms of selected hip extensors as functions of forward lean. A significant forward lean also elongates the hamstring muscles across both the hip and the knee joints. The resulting increased passive tension in these elongated biarticular muscles helps support the partially flexed position of the hips. For these reasons the hamstrings appear uniquely equipped to support the hip during a forward lean. Apparently the nervous system holds the gluteus maximus partially in reserve for more powerful hip extension activities, such as rapidly climbing a flight of stairs.

Acetabular alignment : centre-edge angle and acetabular anteversion angle

(A) The center-edge angle of Wiberg measures the fixed orientation of the acetabulum within the frontal plane, relative to the pelvis. This measurement defines the extent to which the acetabulum covers the TOP of the femoral head. The center-edge angle is measured as the intersection of a vertical, fixed reference line (stippled in red)with the acetabular reference line (bold black solid line)that connects the upper lateral edge of the acetabulum with the center of the femoral head. A more vertical acetabular reference line would result in a smaller center-edge angle, providing less superior coverage of the femoral head. (B) The acetabular anteversion angle measures the fixed orientation of the acetabulum within the horizontal plane, relative to the pelvis. This measurement indicates the extent to which the acetabulum covers the FRONT of the femoral head. The angle is formed by the intersection of a fixed anterior-posterior reference line (stippled in red)with an acetabular reference line (bold black solid line)that connects the anterior and posterior rim of the acetabulum. A larger acetabular anteversion angle creates less acetabular containment of the anterior side of the femoral head. (A normal femoral anteversion of 15 degrees is also shown.) - A hip demonstrating excessive acetabular anteversion is more exposed anteriorly: - when anteversion is severe, the hip is more prone to anterior dislocation and associated lesions of the anterior labrum, especially at the extremes of external rotation. - The likelihood of these associated pathologies increases when acetabular anteversion is combined with excessive femoral anteversion

The near maximal range of femoral-on-pelvic (hip) motion

(A), Sagittal plane (B), Frontal plane (C) Horizontal plane. - Tissues that are elongated or pulled taut are indicated by straight black or dashed black arrows. Slackened tissue is indicated by a wavy black arrow.

Hip internal rotators drive contralateral swinging limb during walking

(R) Pelvic-on-femoral hip internal rotation causes contralateral pelvis (shown as (L) iliac crest) to move forward. The activation pattern of several internal rotator muscles of the right hip is depicted during the first 30% of the gait cycle. (Brighter red indicates greater muscle activation.) Specifically, the tensor fasciae latae, anterior fibers of the gluteus minimus and gluteus medius, and adductor longus are shown rotating the pelvis in the horizontal plane over a relatively fixed right femur.

Stretching an external rotator -piriformis

- Commonly irritated and overused; sciatic nerve passes beneath the piriformis as it exits the greater sciatic foramen to course towards posterior thigh musculature. Muscle spasm or tightness of the deep hip external rotators, especially the piriformis, results in tenderness in the deep gluteal region with accompanying decreased ROM in hip internal rotation and sciatic nerve pain. - As most external rotators switch to internal rotators with increasing hip flexion, a typical stretch of these muscles is performed with the hip and knee flexed and the hip stretched into external rotation, not internal rotation.

Iliofemoral ligament for paraplegic individuals

- A person with paraplegia is shown standing with the aid of braces at the knees and ankles. - Leaning the pelvis and trunk posteriorly orients the body weight vector (red arrow) posterior to the hip joints (small green circle), thereby stretching the iliofemoral ligaments. - This stretch provides a passive flexion torque at the hip, which helps to balance the extension torque generated by gravity. Once counterbalanced, these opposing torques can stabilize the pelvis and trunk, relative to the femur, during standing

Iliopsoas as a 'cause' of low back stress and injury

- A powerful iliopsoas can exert tremendous force on a vulnerable low back unless the abdominal muscles have sufficient strength to provide adequate support. - Since the abdominals contract isometrically once the scapulae are off the floor, it is usually not necessary to perform a full sit-up to strengthen the abdominals. - Maintaining hip flexion at 90°during the abdominal curl limits the amount of force the hip flexors produce during the exercise.

Sit-ups and Straight leg raises (SLRs)

- Abdominals and hip flexors work synergistically in that when one muscle group performs the activity, the other provides stabilization. - 'Abs crunch' - abdominals flexes trunk whilst iliopsoas stabilizes femur; both concentric actions. To go into full sitting, the abdominals stabilize trunk isometrically, further flexion is at the hip by iliopsoas concentrically. (fix femur, flex trunk) - SLR - iliopsoas concentric action, abdominals concentrically stabilizes lumbar spine and pelvis. If performed unilaterally, the contralateral lower extremity is flexed at the hip and knee with the foot and pelvis stabilized (manually), so that abdominals can provide the stabilization of the lumbar spine and pelvis. (fix trunk, flex femur) - unilateral SLR is better, keeping the other leg bent maintains slight posterior pelvic tilt (making the back straight)

Pelvic Rotation in the Frontal Plane

- Abduction of the support hip occurs by raising or "hiking" the iliac crest on the side of the nonsupport hip - Assuming that the supralumbar trunk remains nearly stationary, the lumbar spine must bend in the direction opposite the rotating pelvis. - A slight lateral convexity occurs within the lumbar region toward the side of the abducting hip. - Pelvic-on-femoral hip abduction is restricted to about 30 degrees, primarily because of the natural limits of lateral bending in the lumbar spine. - Marked tightness in hip adductor muscles or the pubofemoral ligament can limit pelvic-onfemoral hip abduction. In the event of a marked adductor contracture, the iliac crest on the side of the nonsupport hip remains lower than the iliac crest of the support hip, which may interfering with walking.

Ligament teres(ligament of head of femur)

- Encased in a flattened sleeve of synovial membrane Function in neonate (a newborn child): - Conduit for small acetabular artery (branch from the obturator artery) to the femoral head - Stabilize fetal hip in the shallow acetabulum Function in adults: - May limit excessive hip internal or external rotation - May function as a sling supporting inferior part of the femoral head during extreme hip flexion/abduction (e.g. squat) - May contribute to proprioception as it seems to contain mechanoreceptors

Shape of the proximal femur

- Factors contributing to the shape of the proximal femur - Differential growth of the bone's ossification centres - Force of muscle activation and weight bearing - Circulation - Consequence of abnormal growth and development -> femoral dysplasia - Clinical implications of shape of proximal femur - Angle of inclination - Femoral torsion

Hip joint

- Femoral head and acetabulum - Ball-and-socket joint - Femoral head : - covered by articular cartilage (thickest around the blue shaded area; about 3.5 mm thick). No cartilage over fovea (small pit found in the head of the femur) - also, muscle, and cancellous bone (spongy or trabecular bone,) in the proximal femur help dampen the large forces that routinely cross the hip.

Pelvic-on-femoral and femoral-on-pelvic hip adduction

- Femoral-on-pelvic hip adduction on the right side - Pelvic-on-femoral hip adduction on the left side; what is the role of the hip abductor on this side As we can see in the picture : - At the right leg, the direction of force from the adductors is from the femur to the pelvis (femoral on pelvic) - At the left leg, the direction of force from the adductor magnus is from the pelvis to the femur (pelvic on femoral) - Furthermore the left gluteus medius is acting eccentrically to prevent excessive lateral tilt.

Acetabular labrum

- Fibrocartilage ring over the rim of the acetabulum; transverse acetabular ligament covering the acetabular notch - Function to deepen joint cavity by approximately 30% and grip the femoral head -> Increased bony congruency and joint stability How does it do it? - By 'gripping' the femoral head, it forms a mechanical 'suction' seal that is effective in resisting the initial 1-2 mm of joint distraction - Also forms a 'fluid seal' that prevents leakage of synovial fluid to more peripheral regions of the hip; maintaining lubrication and helping dissipate contact stress - Poorly vascularized; well supplied by afferent nerves - For this reason, a torn labrum has a very limited ability to heal. - In contrast to its poor vascularization, the labrum is well supplied by afferent nerves capable of providing proprioceptive feedback and, when the labrum is acutely injured, the sensation of pain - The labrum directly protects the articular cartilage by reducing contact stress (force/area) by increasing the surface area of the acetabulum

Hip abductors as important stabilizers during stance in walking

- Gluteus medius, gluteus minimus, and tensor fascia lata provide the primary force for femoral-on-pelvic hip abduction. - Sartorius and piriformis assist in hip abduction when the hip is in flexion. - The greater trochanter deflects the line of pull of gluteus medius laterally by about 2-3 inches (5.0-7.5 cm) from the centre of rotation of the hip, which increases moment arm angle and therefore increasing their torque generation. For these muscles the greatest torque is at their most lengthened position, hence linear relationship.

Sensory innervation of the hip

- Hip capsule, ligaments and acetabular labrum receive sensory innervation through the same nerve roots supplying muscles. Example: - Femoral n. -> anterior joint capsule, anterior thigh - Obturator n. -> antero-medial joint capsule and knee - Sciatic n. -> posterior joint capsule and thigh - Tibial n. -> posterior joint capsule and knee - Peroneal n. -> posterior joint capsule and knee

Iliopsoas is the only hip flexor producing enough force to flex the hip >90 degrees in sitting

- Hip flexors usually work in open chain for moving the lower limb/body forward - Standing -> closed chain position, hip flexors such as iliopsoas tilts pelvis anteriorly. If muscle is tight, pelvis is in anterior pelvic tilt, and compensatory excessive lumbar lordosis. - If iliopsoas are weak, what will happen : - In walking? --- fall backwards - In sitting? --- fall backwards - When leaning back in sitting? --- fall backwards

What happens to people with hip flexion contracture?

- Increased muscular demand on hip extensors and metabolic cost of standing - Optimal overlap of regions with thickest articular cartilage does not occur, so increased wear on joint surfaces - standing with the hips near full extension (proper upright standing) typically directs the force of body weight slightly posterior to the medial-lateral axis of rotation at the hip (small green circle). The force of body weight, therefore, is converted to a very small, but nevertheless useful, hip extension torque. The hip is prevented from further extension by a passive flexion torque created by the stretched capsular ligaments, such as the iliofemoral ligament. - With a hip flexion contracture, the hip remains partially flexed while the person attempts to stand upright. This posture redirects the force of body weight anterior to the hip, creating a hip flexion torque. Whereas gravity normally extends the hip during standing, gravity now acts as a hip flexor. In order to prevent collapse into full hip and knee flexion, active forces are required from hip extensor muscles. In turn, the metabolic cost of standing increases and in some persons, over time, increases the desire to sit. Often, prolonged sitting perpetuates the circumstances that initiated the flexion contracture. - What is the implication for physiotherapy? - maximizing hip extension. In general, this is achieved through strengthening the hip extensor muscles and stretching the hip flexors muscles and the capsular ligaments—most important, the iliofemoral ligament. Activation of the abdominal muscles through posterior tilting of the pelvis may also encourage extension of the hip joint. The capsular ligaments of the hip may be further stretched when extension is combined with slight abduction and internal rotation—the close-packed position of the hip. - People 75-86 years old walk with 30% less hip extension than younger people.

Arthrokinematics

- Nearly spherical femoral head articulated snugly in the near-spherical (hemispheric but acetabular notch completed with the transverse acetabular ligament to make it spherical). - But convex-concave rule still applies in the hip joint - Accessory movements within the hip joint < 2 mm. Implications?

Pelvis and Hip

- Stability vs mobility Shoulder girdle vs pelvic girdle : - Hip joint -> articulation between pelvic girdle fossa (acetabulum) and femoral head - shoulder joint -> glenoid fossa and humeral head - What are the challenges in hip joint cf. shoulder joint? - Transmit large forces between trunk and ground, e.g. hip abductor muscles on the weight-bearing leg must counterbalance about 85% of body's weight with every step - Elevate and lower body - Locomote

Unilateral stance : carrying loads should be done on ipsilateral side or contralateral side, why?

- Standing on one leg produces a high compressive force between the femoral head and acetabulum (about 2.5 times to 4 times body weight). - Hence degenerative changes occur in a painful hip or in obesity. An individual with unilateral hip pain or degeneration should carry an object with the ipsilateral arm since it will place less compression force on the hip joint. Its moment arm is shorter than an object carried with the contralateral arm, so its joint reaction force will also be less. On the other hand, the moment arm and subsequent torque of an object carried with the contralateral arm is significantly greater, so the joint reaction force applied by the torque of the object is concomitantly greater.

Femoral-on-pelvic hip flexion

- Strong hip flexors (e.g. rectus femoris) not only flexes hip but also anteriorly tilts pelvis - The action of moderate- to high-power hip flexion requires coactivation of the hip flexor and abdominal muscles. This intermuscular cooperation is apparent when the leg is lifted while the knee is held in extension (i.e., a "straight-legraise" movement). - This action requires that the rectus abdominis (a representative "abdominal" muscle) generate a potent posterior pelvic tilt effort that is strong enough to neutralize the strong anterior pelvic tilt potential of the hip flexor muscles - Strong abdominals are therefore required to stabilize the pelvis. What will happen if abdominals are weak? - Without sufficient stabilization from the abdominal muscles, contraction of the hip flexor muscles is inefficiently spent tilting the pelvis anteriorly ( shown in B ) - What happens if knee is flexed?

Joint capsule

- Synovial membrane lines the internal surface of the joint capsule - The ligaments reinforce the external surface of the capsule. - Passive tension in stretched ligaments, the adjacent capsule, and the surrounding muscles help define the end-range of movements of the hip The anterior capsule and ligaments of the right hip. The iliopsoas, consisting of the iliacus and psoas (major), has been cut away to expose the anterior side of the joint. Note that part of the femoral head protrudes just medial to the iliofemoral ligament. This region is covered by the joint capsule and, in some cases, also by a bursa.

Articulating surface -'lunate surface'

- The acetabulum (from Latin, meaning "vinegar cup") is a deep, hemispheric cuplike socket that accepts the femoral head. About 60 to 70 degrees of the rim of the acetabulum are incomplete near its inferior pole, creating the acetabular notch - Femoral head articulates the acetabulum only along a horseshoe-shaped lunate surface - Lunate surface -covered by articular cartilage, thickest about 3.5 mm, corresponding to the area of highest joint forces encountered during walking (see next slide) - Acetabular fossa is a depression within the floor of acetabulum that is without articular cartilage. Why? Then what is its function? - Instead, the fossa contains the teres ligament, fat, synovial membrane, and blood vessels. During walking, hip forces fluctuate between 13% of body weight during midswing phase to 300% of body weight during midstance phase. Graph shows a computer model's estimate of the hip joint compression force as a multiple of body weight during the gait cycle. The stance phase is between 0% and 60% of the gait cycle, and the swing phase is between 60% and 100% of the gait cycle (vertical stippled line separates these major divisions of the gait cycle). The images above the graph indicate the approximate area of acetabular contact at three selected magnitudes of hip joint force, estimated by data published in the literature. The area of joint contact increases from about 20% of the lunate surface during the swing phase to about 98% during mid stance phase.

Pelvic-on-femoral hip extension

- The force-couple between hip extensors (gluteus maximus bdominis and obliquus externus abdominis) posteriorly tilts the pelvis. - Note the decreased lordosis at the lumbar spine. The extension at the hip stretches the iliofemoral ligament. - Anterior capsule and hip flexor muscles limit posterior pelvic tilt. - During standing, a combination of tension in the hip's capsular ligaments and hip flexor muscles normally determines the endrange of the posterior pelvic movement. - Interestingly, unlike the end-range of an anterior pelvic tilt, the lumbar spine does not normally restrict the end-range of the posterior pelvic tilt. - Hip Extensors Controlling a Forward Lean of the Body. - Leaning forward while standing is a very common activity. Consider, for example, the forward lean used to brush your teeth over a sink - The muscular support at the hip for this near static posture is primarily the responsibility of the hamstring muscles

Innervation of muscles

- The nerves of the lumbar plexus pass anterior of the hip joint and mainly support the anterior portion of the thigh. - The sacral plexus provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, as well as part of the pelvis. 1. Femoral nerve - flexion at hip and extension at knee 2. Obturator nerve - adduction of thigh 3. Sciatic nerve - flexion at knee 4. Tibial nerve - foot plantar flexion and inversion, and toe flexion 5. Common peroneal nerve - foot eversion (superficial peroneal nerve.) and foot dorsiflexion, toe extension (deep peroneal nerve.)

Average maximal effort torque of each muscle group of hip : which is the strongest? which is the weakest?

- The primary hip flexors are the iliopsoas, sartorius, tensor fasciae latae, rectus femoris, adductor longus, and pectineus. - Secondary hip flexors are the adductor brevis, gracilis, and anterior fibers of the gluteus minimus

Pelvic Rotation in the Sagittal Plane: Anterior and Posterior Pelvic Tilting

- While sitting with 90 degrees of hip flexion, the normal adult can perform about 30 degrees of additional pelvic-on-femoral hip flexion before being restricted by a completely extended lumbar spine. - Full anterior tilt of the pelvis slackens most of the ligaments of the hip, most notably the iliofemoral ligament. Marked tightness in any hip extensor muscle—such as the hamstrings—could theoretically limit the extremes of an anterior pelvic tilt. - the hips can be extended about 10 to 20 degrees from the 90-degree sitting posture via a posterior tilt of the pelvis. - During sitting, this short-arc pelvic rotation would increase the length (and therefore tension) only minimally in the iliofemoral ligament and rectus femoris muscle. As depicted in the figure, the lumbar spine flexes, or flattens, as the pelvis posteriorly tilts.

Hip joint ligaments

1. iliofemoral ligament 2. ischiofemoral ligament 3. pubofemoral ligament 4. ligamentum teres

So what is the optimal angle for femoral and hip joint congruence in terms of angle of inclination and femoral torsion

125 degrees for angle of inclination with 15 degrees of anteversion

What is angle of inclination and what happens if its an abnormal angle

Angle of inclination : - Angle in frontal plane between femoral neck and shaft. - At birth -> 165-170°but decreases by 2° per year from 2-8 yo - Normal adult -> 125° - Coxa vara ( vara, to bend inward) <125°and coxa valga (to bend outward) >125° - The angle of inclination increases leverage of the muscles that connect the pelvis to the greater trochanter. What happens if abnormal angle? - Children with developmental disorders, e.g. cerebral palsy and spinabifida, often present with coxa valga. Why? - Delayed motor development - Limited movement - Abnormal muscular forces on malleable bones - Consequences? - Hip instability - Decreased muscle leverage - Reduced force production capability - Older persons tend to have coxa vara -> predispose to fall and hip fracture

some pictures of hip abductor weakness and which hand we should hold the cane with

B) Pelvic alignment in unimpaired unilateral stance. C) With hip abductor weakness on the right, an attempt to raise the left leg off the floor results in pelvic drop on that side (Trendelenberg sign). (D) Placing a cane in the individual's left hand (contralateral to the weak gluteus medius on the right) provides a force platform through which the pelvis remains level. E) With the cane used in the hand contralateral to the affected lower extremity, the long moment arm that is created requires little force exerted through the cane to provide sufficient support during ambulation. 1 shows the moment arm length of the body weight and 2 represents the moment arm length of the assistive device when placed in the contratateral upper extremity; notice the significantly larger moment arm with the device on the opposite side to the affected lower extremity.

Hip internal rotation torques increase with hip flexion, Hip external rotators can switch to become hip INternal rotators?!?!

Even some of external rotators (e.g. posterior fibres of gluteus medius, piriformis, ant./sup. fibres of gluteus maximus and post. fibres of gluteus minimus switch actions and become internal rotators when the hip is flexed to 60 degrees or more.

What is femoral torsion (anteversion, retroversion)? and what happens if there is excessive anteversion

Femoral torsion : - Relative rotation between femoral shaft and neck - as viewed from above, the femoral neck projects about 15 degrees anterior to a medial-lateral axis through the femoral condyles - At birth -> 40°anteversion - but by 16 yo : Normal anteversion-> 8-20°anteriorly Normally 15°; abnormal if: >15°-> Excessive anteversion <15°-> Retroversion What happens if excessive anteversion? - Especially in children with developmental disorders when the femur has not yet fully derotated so walking with 'in-toeing' gait. - In-toeing is a walking pattern with exaggerated posturing of hip internal rotation. - standing with the hip internally rotated ("intoeing") improves the joint congruity - exaggerated internally rotated position during walking serves to increase the moment arm of the important hip abductor muscles—leverage that is substantially reduced with excessive femoral anteversion - Excessive anteversion that persists into adulthood can increase the likelihood of hip dislocation, articular incongruence, increased joint contact force, and increased wear on the articular cartilage. These factors may lead to secondary osteoarthritis of the hip - What happens to the hip muscles if long-term in-toeing gait? - over time, develop shortening of the internal rotator muscles and various ligaments, thereby reducing external rotation range of motion. - Common in persons with cerebral palsy (25 to 40 degrees)

Pelvic-on-femoral hip flexion : force coupling of what?

Force-couple between hip flexors and trunk extensors With fixed femurs, contraction of the hip flexors rotates the pelvis about the medial-lateral axis through both hips. Excessive/reduced anterior pelvic tilt and lumbar lordosis may be due to : 1. Postural habits 2. Pain avoidance 3. Poor sitting posture 4. Compensation from thoracic lordosis/ excessive kyphosis 5. Weak abdominals or tight hip extensors 6. Tight connective tissues

Close-packed position of the hip : the position that creates the greatest stretch in the capsular ligaments

Full hip extension (>20 degrees), slightly internally rotated and slightly abducted - This position is useful therapeutically during attempts to stretch the entirety of the hip's capsular ligaments - In many other joints of the body, the position that stretches most of the ligaments is also the position where the joint is most congruent. - This is not the case with the hip; the hip is most congruent in 90 degrees of flexion, external rotation, and abduction. A, The hip is shown in a neutral position, with all three capsular ligaments identified. B, Superior view of the hip in its close-packed position (i.e., fully extended with slight abduction and internal rotation). This position elongates at least some component of all three capsular ligaments.

Hip external rotators

Gluteus maximus and 6 "short external rotators" Short external rotators: 1. Piriformis 2. Obturator internus 3. Gemellus superior 4. gemellus inferior 5. Quadratus femoris 6. Obturator externus

What are the hip muscles that cross 2 joints?

Hip muscles that cross 2 joints 1. Rectus femoris 2. Sartorius 3. Tensor fascia lata 4. Gracilis 5. Hamstring group - Most muscles can only shorten to about 70% of their resting length, so the greatest force at one joint could only occur if the muscle is lengthened at the other joint. - When a two-joint muscle shortens over both of its joints simultaneously, it encounters active insufficiency.

Osteology

Innominate is the union of 3 bones: 1. Ilium 2. Pubis 3. Ischium - Osteoligamentous ring -> pelvis - Muscle attachment for trunk and LL - Transmission of weight of UL/trunk - Supports organs of bowel, bladder and reproductive functions Acetabulum is made up of 40% ischium, 40% ilium and 20% pubis

Isometric Torques at Different Joint Angles

Internal torque versus joint angle curve of two muscle groups under isometric, maximal-effort conditions. The shapes of the curves are very different for each muscle group. (A) Internal torque of the elbow flexors is greatest at an angle of about 75 degrees of flexion. (B) Internal torque of the hip abductors is greatest at a frontal plane angle of −10 degrees (i.e., 10 degrees of adduction).

Lumbopelvic rhythm : ipsidirectional and contradirection lumbopelvic rhythm

Ipsidirectional lumbopelvic rhythm : - pelvis and lumbar spine rotate in the same direction. - The effect of this movement is to maximize the angular displacement of the entire trunk relative to the lower extremities—an effective strategy for increasing reach of the upper extremities - bending down Contradirectional lumbopelvic rhythm : - the pelvis rotates in one direction while the lumbar spine simultaneously rotates in the opposite direction - The important consequence of this movement is that the supralumbar trunk (i.e., that part of the body located above the first lumbar vertebra) can remain nearly stationary as the pelvis rotates over the femurs. - This type of rhythm is used during walking, for example, when the position of the supralumbar trunk—including the head and eyes—needs to be held relatively fixed in space, independent of the rotation of the pelvis - A person with a fused lumbar spine is therefore unable to rotate the pelvis about the hips without a similar rotation of parts of the supralumbar trunk. This abnormal situation is readily apparent when the individual walks.

Hip adductors as flexors and extensors

Outside 40-70 degrees range, adductor longus can be a flexor or extensor of the hip. - The dual sagittal plane action of the adductor longus muscle is demonstrated during sprinting. (A) With the hip flexed, the adductor longus is in position to extend the hip, along with the adductor magnus. (B) With the hip extended, the adductor longus is in position to flex the hip, along with the rectus femoris. - These contrasting actions are based on the change in line of force of the adductor longus, relative to the medial-lateral axis of rotation at the hip.

Iliofemoral ligament ("Y" ligament or ligament of Bigelow)

Proximal attachment : AIIS and iliac portion of acetabulum Distal attachment : As a thickening of the anterior and superior joint capsule, attaches to the intertrochanteric line of femur Motion it limits (what makes it taut) : hip extension, especially hyperextension; superior portion limits adduction and lateral portion limits some lateral rotation; also limits pelvic posterior tilt. - The iliofemoral ligament is the strongest and stiffest ligament of the hip. - When a person stands with the hip fully extended, the anterior surface of the femoral head presses firmly against the iliofemoral ligament and superimposed iliopsoas muscle - From a position of standing, passive tension in these structures forms an important stabilizing force that resists further hip extension.

Ligamentum teres(means ligament to the head; teres meaning round as in femoral head

Proximal attachment : Center of acetabular fossa Distal attachment : Fovea of femoral head Motion it limits : Prevents extreme limits of adduction, flexion and lateral rotation or adduction, extension and medial rotation. Primary function: serves as a conduit for a branch of obturator artery (fovealartery) to deliver blood supply to femoral head

Ischiofemoral ligament

Proximal attachment : Ischial portion of acetabulum rim and labrum, posteriorly and inferiorly Distal attachment : As a thickening of posterior and lateral capsule, attaches to posterior aspect of femoral neck near apex of greater trochanter medially Motion it limits : Hip extension, abduction and medial rotation; limits hyperflexion; superior fibers limit extreme adduction (especially when hip is flexed); also limits ipsilateral pelvic rotation.

Pubofemoral ligament

Proximal attachment : Pubis (anterior aspect of superior ramus) and anterior-medial or pubic portion of acetabular rim Distal attachment : As a thickening of anterior and inferior capsule, attaches to anterior intertrochanteric fossa and to neck of femur, posteriorly Motion it limits : hip extension, abduction and lateral rotation; also limits ipsilateral pelvic lateral tilt

Structures that are taut at end range ROM

Rotation of the Femur in the Sagittal Plane (Femoral-on-pelvic rotation) - On average, with the knee flexed, the hip flexes to about 120 degrees. Tasks such as comfortably squatting or tying a shoelace typically require this amount of hip flexion. - Full hip flexion slackens the three primary capsular ligaments but stretches the inferior capsule and muscles such as the gluteus maximus. With the knee fully extended, hip flexion is typically limited to 70 to 80 degrees by increased tension in the hamstring muscles. - The hip normally extends about 20 degrees beyond the neutral position. Full hip extension increases the passive tension throughout the capsular ligaments—especially the iliofemoral ligament and the hip flexor muscles. When the knee is fully flexed during hip extension, passive tension in the stretched rectus femoris, which crosses both the hip and the knee, reduces hip extension to about the neutral position Rotation of the Femur in the Frontal Plane : - The hip abducts on average about 40 degrees, limited primarily by the pubofemoral ligament and the adductor muscles. - The hip adducts about 25 degrees beyond the neutral position. In addition to interference with the contralateral limb, passive tension in stretched hip abductor muscles, iliotibial band, and superior fibers of the ischiofemoral ligament limits full adduction. Rotation of the Femur in the Horizontal Plane : - The magnitude of internal and external rotation of the hip is particularly variable among subjects. On average, the hip internally rotates about 35 degrees from the neutral position. - With the hip in extension, maximal internal rotation elongates the external rotator muscles, such as the piriformis, and parts of the ischiofemoral ligament. - The extended hip externally rotates on average about 45 degrees. Excessive tension in the lateral fasciculus of the iliofemoral ligament can limit full external rotation. - In addition, external rotation can be limited by excessive tension in any internal rotator muscle.

Hip Abductor Mechanism: Role in the Production of Compression Force at the Hip

The forces created by active hip abductors and body weight create opposing torques that control the position and stability of the pelvis (within the frontal plane) over the femoral head. During single-limb support, the pelvis is comparable to a seesaw, with its fulcrum represented by the femoral head. When the seesaw is balanced, the counterclockwise (internal) torque produced by the right hip abductor force (HAF) equals the clockwise (external) torque caused by body weight (BW). Balance of opposing torques is called static rotary equilibrium. - As the centre of gravity of the body shifts laterally over the supporting foot in unilateral stance, the hip tends to be adducted. The ipsilateral hip abductors maintain the pelvis to balance the weight of the head, arms and trunk and contralateral leg. Hence there is a compressive force applied in the ipsilateral hip joint. - internal moment arm (D) used by the hip abductor muscles is about half the length of the external moment arm (D1) used by body weight. - Given this length disparity, the hip abductor muscles must produce a force twice that of body weight in order to achieve stability during single-limb support. - On every step, therefore, the acetabulum is pulled against the femoral head by the combined forces produced by the hip abductor muscles and the pull of body weight. - To achieve static linear equilibrium, this downward force is counteracted by a joint reaction force (JRF) of equal magnitude but oriented in nearly the opposite direction

Osteokinematics : femoral-on-pelvic and pelvic on femonal (important)

The osteokinematics of the right hip joint. Femoral-on-pelvic and pelvic-on-femoral rotations occur in three planes. - The axis of rotation for each plane of movement is shown as a colored dot, located at the center of the femoral head. (A) Side view shows sagittal plane rotations around a medial-lateral axis of rotation. (B) Front view shows frontal plane rotations around an anterior-posterior axis of rotation. (C) Top view shows horizontal plane rotations around a longitudinal, or vertical, axis of rotation.

Another cause of adductor muscle strain: strong pelvic-on-femoral hip abduction during sudden pelvic/trunk rotation during running

The right LL pivoted to the ground, external rotators contract strongly to bring the contralateral pelvis posteriorly. The strong gluteus maximus and external rotator torque is countered by the eccentric action of the internal rotators, particularly adductor longus and brevis. (thus straining the adductors)

Femoral-on-pelvis hip extension -not just gluteus maximus and hamstring : climbing a mountain

hip extensor muscles are frequently required to produce large and powerful femoral-on-pelvic hip extension torque to accelerate the body forward and upward Relatively high demands are placed on many muscles that cross the hip, knee, and ankle as one climbs a mountain while bearing an external load. Activation is also required in low back extensor muscles (such as, for example, the lower multifidus) to stabilize the position of the pelvis. Note the medial-lateral axis of rotation at the hip and knee. - Furthermore, with the hip markedly flexed, many of the adductor muscles can produce an extension torque, thereby assisting the primary hip extensors.