Distal articular structure

Accessory structure

HIP JOINT CAPSULE

The hip joint capsule is irregular dense fibrous structure with longitudinal and oblique fibers and three thickened regions that constitute the capsular ligaments. The capsule is thickened anterosuperiorly , where there is little bony support and predominant stresses occur. Posterioinferiorly ,the capsule is relatively thin and redundant, with some areas of the capsule thin enough to be nearly translucent. The capsule of hip joint covers the femoral head and neck like a cylindrical sleeve and attaches to the base of the femoral neck.

HIP JOINT LIGAMENTS

1. Ileofemoral ligament is fan shaped and resembles an inverted letter Y and is often referred to as the Y ligament of Bigelow. The apex of the ligament is attached to the anterior inferior iliac spine, and the two arms of the Y fan out to attach along the intertrochanteric line of femur. The superior band of the ileofemoral ligament is strongest and thickest of the hip joint ligaments.

   Function

   • It help in prevention of falling back
   • It also help in prevention of lateral rotation
2. Pubofemoral ligament is also anteriorly located, arising from the pubic portion of the acetabular rim inferior and medial to the iliopectinal eminence. The pubofemoral ligament forms a sling that supports the inferior aspect of the femoral neck and connects fibers of the iliofemoral and ischiofemoral ligaments.

   Function

   • It resist lateral rotation in extension
3. Ischofemoral ligament is the posterior capsular ligament and attaches to the posterior surfaces of the acetabular rim and the acetabular labrum.

   Function

   • It resist medial rotation in extension.

Trabecular systems of hip joint

The internal architecture of the pelvis and femur reveals the remarkable interaction between mectanical stresses and structural adaptation created by the transmission of force between the femur and the pelvis. The trabeculae ( calcified plates of tissue within the cancellous bone ) line up along lines of stress and form systems that normally adapt to stress requirement . Most weightbearing stresses in the pelvis pass from the sacroiliac joints to the acetabulum.

In standing or upright weightbearing activities, atleast half the weight of the HAT ( the gravitational forces )passes down through the pelvis to each femoral head. Because this compressive force passes medially to the femoral neck, a moment arm exist that creat a bending moment acoss the femoral neck of glenohumeral joint . This moment arm is the perpendicular distance between the superimposed body weight on the femoral head and the intertrochanteric area. As a result of thi bending moment the femoral neck is subjected to a tensile force on the superior aspect of the femoral neck and a compressive force on the inferior aspect. Bone naturally responds better to compressive force than tensile force .

The body able to minimize this tensile load by the incorporation muscle activity across the hip which can create large compressive forces across the femoral neck to offset the imposed tensile force due to the weight of the HAT. In additional ,a complex set of forces within the femoral neck prevents the rotation of the neck on the shaft; among these forces are the structural resistance of two major and three minor trabecular systems.

1. Medial compressive system
2. Lateral tensile trabecular system
3. Secondary compressive system
4. Secondary tensile system
5. Trochanter system

Function

Motion of the femur on the acetabulum

Flexion and extension of the femur occur from a neutral position as analmost pure spin of the femoral head around a coronal axis through the head and neck femur.it include both spinning and gliding of articular surface of hip joint . Flexion of the hip joint is generally about 90degree with knee extended, and 120 degree when the knee is flexed . Extension is 10 – 30 degree.

Abduction and adduction of the femur is 45 – 50 degree and 20 – 30 degree respectively . In , adduction the head of femur move upward while distal part moving inward. In abduction the head of femur move inferiorly and distal part of femurs move superiorly.

Motion of acetabulum on the femur

Anterior and posterior pelvic tilt are motion of in sagittal plane around a coronal axis .Anterior pelvic tilt occur in hip joint when anterior superior iliac spine ( ASIS )move anteriorly and inferiorly . Lateral pelvic tilt is frontal plane motion of entire pelvis around an anteroposterior axis. The weightnbearing hip joint serve as the pivot point or axis for motion of the pelvis as the pelvis either elevates (pelvic hike ) or drops (pelvic drop) in the frontal planes.

Lateral shift of the pelvis

Lateral pelvic tilt can also occur in bilateral stance. If both feet are on ground and the hip and knee of one limb are flexed, the opposite limb is largely the weightbearing limb and the terminology is the same as for unilateral stance. However if both limbs are weightbearing, lateral tilt of the pelvis will cause the pelvis shift to one side or the other .

Forward rotation of the pelvis in a bilateral stance, when the side of the pelvis opposite to the weightbearing hip joint moves anteriorly from the neutral position . forward rotation of pelvis produces medial rotation of the weightbearing hip joint .

Backward rotation of the pelvis occurs when the side of the pelvis opposite the weightbearing hip moves posteriorly.backward rotation of the pelvis produces lateral rotation of the weight bearing hip joint .

Hip joint musculature

Flexors

Nine muscle of anterior aspect of the hip joint :rectus femoris , iliacus,psoas major . tensor fascia latae, Sartorius ,adductor longus, adductor magnus and gracilis.

Extensors

Muscles like gluteus medius , gluteus maximus, long head of biceps femoris , the semitendenosus and semimembranosus .

Adductor

The hip joint adductor muscle groups is generally considered to the pecteneus, adductor bervis , adductor longus, adductor magnus and gracilis muscle.

Abductors

The have been likened to the rotator cuff muscle of hip joint with gluteus medius and gluteus minimus .