Why are fractures across the femoral neck common, especially among elderly women? How does the blood supply of the femoral head play a role in the critical nature of the injury?

What will be an ideal response?

ANS:
The angle of inclination between the neck and the femoral shaft results in a shearing force across the neck. That is, the weight-bearing line of HAT (head, arms, and trunk) comes down on the head of the femur, while the normal force of the ground travels up the femoral shaft. These two lines of force lie at a distance from each other, creating a shear across the neck. Ordinarily the bone is adequate to withstand this stress, but when the bone weakens (as it does in osteoporosis that accompanies aging), the shear at the neck may result in a fracture across the vulnerable area of the neck, which can occur from what would previously have been incidental forces. Because the primary blood supply to the femoral head is obtained through the circumflex arteries, a fracture of the neck may interrupt the blood supply to the head, resulting in avascular necrosis. In those individuals with a decent blood supply through the ligamentum teres, the situation is somewhat less critical.