Hip Joint 1

Biomechanics Of Hip Joint Also called as coxofemoral joint Articulation of head of femur with acetabulum of pelvis Diarthrodial ball & socket joint with 3° freedom movement Flexion/Extension – saggital plane Abduction/adduction – frontal plane Medial/Lateral rotation – transverse plane

• Primarily structured to serve weight bearing

function • Function of this joint is to support weight of the head,arms & trunk (HAT) both in static erect posture and in dynamic postures such as ambulation,running and stair climbing

Structure of Hip Joint: Proximal Articular surface: Acetabulum- pubis 1/5th, ischium2/5th, ilium the remaining Horse shoe shaped portion of the periphery is covered with hyaline cartilage and articulates with the head of femur Inferior aspect is called as acetabular notch Central deepest portion called acetabular fossa is nonarticular and contains fibroelastic fat covered with synovial membrane and femoral head doesn't articulate this area

 Center edge of angle/angle of Wiberg:

Acetabulum is oriented on the pelvis to face laterally,inferiorly and anteriorly Used to assess the magnitude of inferior orientation of acetabulum and is assessed using CT scan Angle between line connecting the lateral rim of acetabulum & center of femoral head 38° - males 35° - females Smaller angle may result in diminished coverage of head of femur Increased risk of superior dislocation of head of femur

Center-edge angle or angle of Wiberg(1) - Normally 30° to 40°, this angle represents the degree of femoral head coverage in the frontal plane. An angle of less than 30° is a characteristic sign of hip dysplasia

 Acetabular Anteversion:

Magnitude of anterior orientation of acetabulum is referred as angle of acetabular anteversion 18 .5° - males 21.5° - females Pathological increases are associated with decreased joint stability and increased tendency for anterior dislocation of head of femur

 Acetabular labrum:

Given the need for stability, hip joint has an accessory structure in the form of labrum which is fibro cartilage Entire periphery of the acetabulum is rimmed by ring of wedge-shaped labrum which is fibrocartilage Labrum not only deepens the socket but increases the concavity Transverse acetabular ligament is a part of the labrum and spans the articular gap at the base of the articular horseshoe

Distal articulating surface: Head of Femur: • Rounded hyaline cartilage covered surface • Inferior to the most medial point a pit called fovea capitis is present which is not covered with cartilage and is the point at which the ligament of head of femur is attached • Head is attached to the neck which is angulated so the head faces medially, superiorly and anteriorly

Angulation of Femur: There are 2 angulations made by head & neck of femur relative to the shaft  Angle of inclination (neck shaft angle): Occurs in frontal plane Angle between an axis through femoral head and neck and the longitudinal axis of femoral shaft Early infancy-150° Adult-125° Elderly –120°

• Pathologic increase in medial angulation is

called as COXA VALGA and results in increase in leg length • Pathologic decrease is called as COXA VARA and there is decrease in leg length

Angle of inclination

COXA VALGA

COXA VARA

Angle of inclination (2)- This angle, between the femoral neck and the shaft of the femur, is normally 125°. In hips with dysplasia, it is commonly increased but also may be decreased

Coxa Valga

X-ray - normal left side and coxa vara on right side

 Angle of Torsion:

Occurs in transverse plane When femur is viewed from above with the axis of the femoral condyles neck of the femur is seen to have an anterior angle Axis through the femoral head and neck will make an angle with an longitudinal axis through the distal femoral condyles that reflects anterior twisting of head and neck in relation to condyles

Best viewed by looking down the length of the femur from top to bottom Axis through the head and neck will lie at an angle to the axis through the condyles This angulation reflects the twist in the bone Normal range is 10°-15° Normal angle of torsion is referred as anteversion as angle is made anteriorly

Pathologic increase – anteversion(more than normal 10° –15°) and is one factor considered to cause in-toeing or pigeon toe

Angle of torsion

Anteversion

Pathologic decrease – retroversion which may lead to out toeing

Angle of torsion

Retroversion

Angle of torsion Anteversion

in-toeing

Retroversion

out toeing

Articular congruence: • Hip is a congruent joint • In neutral standing articular surface of the femoral head remains exposed anteriorly and superiorly • Acetabulum does not fully cover the head superiorly • In neutral hip joint articular cartilage of the head of femur is exposed anteriorly and to a lesser extent superiorly

Maximum articular contact of head of femur with acetabulum is obtained when femur is flexed,abducted and laterally rotated(frog-leg position) This position is used for immobilization when the goal is to improve articular contact and joint congruence in cases of CDH & Legg-Calve-Perthes disease