BIO-MECHANICS OF HIP JOINT Lecture-2 BIO-MECHANICS OF HIP JOINT Prepared by: Dr. Hazrat Bilal DPT (IPMR, KMU)

Objectives At the end of this lecture the students shall be able to: Enumerate the basic anatomy of distal particular surface of the hip joint Describe the angle of inclination Describe the angle of torsion Identify pathological angle of inclination and torsion

Distal articular surface

Distal Articular Surface The head of the femur is a fairly rounded hyaline cartilage-covered surface that may be slightly larger than a true hemisphere or as much as two thirds of a sphere. The head of the femur is considered to be circular, unlike the more irregularly shaped acetabulum.

Just inferior to the most medial point on the femoral head is a small roughened pit called the fovea or fovea capitis. The fovea is not covered with articular cartilage and is the point at which the ligament of the head of the femur is attached.

The femoral head is attached to the femoral neck; the femoral neck is attached to the shaft of the femur between the greater trochanter and the lesser trochanter. The femoral neck is, in general, only about 5 cm long. The femoral neck is angulated so that the femoral head most commonly faces medially, superiorly, and anteriorly.

Angulation of the Femur There are two angulations made by the head and neck of the femur in relation to the shaft. Angle of inclination Angle of torsion

Angle of Inclination of the Femur The angle which is formed between the longitudinal axis of the shaft and neck of femur. The angle of inclination of the femur averages 126°, ranging from 115° to 140° in the unimpaired adult

As with the angle of inclination of the femur, there are variations not only among individuals but also from side to side. In women, the angle of inclination is somewhat smaller than it is in men, owing to the greater width of the female pelvis. With a normal angle of inclination, the greater trochanteric lies at the level of the center of the femoral head.

Coxa valga and vara The angle of inclination of the femur changes across the life span, being substantially greater in infancy and childhood and gradually declining to about 120° in the normal elderly person. A pathologic increase in the medial angulation between the neck and shaft is called coxa valga and a pathologic decrease is called coxa vara.

http://www. kypma. com/docs/LangerBiomech%20Kim%20Ross. pdf http://www http://www.kypma.com/docs/LangerBiomech%20Kim%20Ross.pdf http://www.feetonthehill.co.uk/feetonthehill/export/sites/default/PdfFolder/CaseStudyPDFs/CoxaValgaand_Anterversion.pdf

Angle of Torsion of the Femur The angle which is formed between two transverse parallel line of the femoral neck and femoral condyels

Angle of Torsion of the Femur The angle of torsion of the femur can best be viewed by looking down the length of the femur from top to bottom. An axis through the femoral head and neck in the transverse plane will lie at an angle to an axis through the femoral condyles, with the head and neck torsioned anteriorly (laterally) with regard to an angle through the femoral condyles.

This angulation reflects the medial rotatory migration of the lower limb bud that occurred during fetal development.

The angle of torsion decreases with age The angle of torsion decreases with age. In the newborn, the angle of torsion has been estimated to be 40°, decreasing substantially in the first 2 years. Researchers found a decrease of approximately 1.5° per year until cessation of growth among children with both normal and exaggerated angles of anteversion. In the adult, the normal angle of torsion is considered to be 10° to 20°.

Antewversion /retroversion A pathologic increase in the angle of torsion is called anteversion and a pathologic decrease in the angle or reversal of torsion is known as retroversion

Heller and colleagues used an angle of 30° to model effects of anteversion, acknowledging that children with cerebral palsy have demonstrated angles of 60° or more. Noble and colleagues found an average angle of 16° among 154 women diagnosed with developmental hip dysplasia who had not had surgical intervention.

It should be recognized that both normal and abnormal angles of inclination and torsion of the femur are properties of the femur alone (i.e., both can be measured or assessed independently of the continuous bones, However, abnormalities in the angulations of the femur can cause compensatory hip changes and can substantially alter hip joint stability, the weight- bearing biomechanics of the hip joint, and muscle biomechanics.

Although some structural deviations such as femoral anteversion and coxa valga are commonly found together, each may occur independently of the other. Each structural deviation warrants careful consideration as to the impact on hip joint function and function of the joints both proximal and distal to the hip joint.

Femoral anteversion is often implicated in dysfunction at both the knee and at the foot. The other pathologic angulations of the femur (retroversion, coxa vara, and coxa valga) similarly affect the hip joint and other joints proximally and distally.

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