WKI Sales Training Feb 2014

Chapter 5 • Lower Limb

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blood supply to the femoral head and in post-traumatic avascu- lar necrosis of the head of the femur. As a result, incongruity of the joint surfaces develops, and growth at the epiphysis is retarded. Such conditions, most common in children 3–9 years of age, produce hip pain that may radiate to the knee.

FIGURE B5.29.

Dislocation of Hip Joint

Congenital dislocation of the hip joint is common, occurring in approximately 1.5 per 1000 neonates; it is bilateral in approximately half the cases. Girls are affected at least eight times more often than boys (Salter, 1999). Dislocation occurs when the femoral head is not prop- erly located in the acetabulum. Inability to abduct the thigh is characteristic of congenital dislocation. In addition, the affected limb appears (and functions as if it is) shorter because the dislocated femoral head is more superior than on the normal side, resulting in a positive Trendelenburg sign (hip appears to drop on one side during walking). Approximately 25% of all cases of arthritis of the hip in adults are the direct result of residual defects from congenital dis- location of the hip. Acquired dislocation of the hip joint is uncommon because this articulation is so strong and stable. Nevertheless, disloca- tion may occur during an automobile accident when the hip is flexed, adducted, and medially rotated, the usual position of the lower limb when a person is riding in a car. Posterior dislocations of the hip joint are most common. A head-on collision that causes the knee to strike the dashboard

maintaining the femoral head; consequently, the fragment may undergo aseptic vascular necrosis (tissue death) .

Surgical Hip Replacement

Although the hip joint is strong and stable, it is sub- ject to severe traumatic injury and degenerative disease. Osteoarthritis of the hip joint, character- ized by pain, edema, limitation of motion, and erosion of articular cartilage, is a common cause of disability (Fig. B5.30A). During hip replacement, a metal prosthesis anchored to the person’s femur by bone cement replaces the femoral head and neck (Fig. B5.30B). A plastic socket cemented to the hip bone replaces the acetabulum.

Cartilage Hip bone

Cartilage

Femur

Normal hip

Osteophytes and eroded

articular cartilage

(A)

(B) Hip prosthesis

(A) Hip with moderate arthritis

FIGURE B5.30.

Head of femur is driven posteriorly, out of acetabulum

Necrosis of Femoral Head in Children In children, traumatic dislocations of the hip joint disrupt the artery to the head of the femur. Fractures that result in separation of the superior femoral epiphysis (the growth plate between the femoral head and neck) are also likely to result in an inadequate

(B)

Posterior dislocation of the right hip joint

FIGURE B5.31.

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