The most common site of avascular necrosis of fracture neck of femur is (AIIMS Nov 2009)
Sub capital i.e, # Just below the head
Transcervical i.e. # in the middle of the neck
Basal ie. # base of the neck.
• Up to the age of 4 months the femoral head is supplied by
a. Metaphyseal vessels which penetrate the growth disc
b. Lateral epiphyseal vessels running in the retinacula
c. Scanty vessels in the ligamentum teres
The metaphyseal supply gradually declines until by the age of 4 years, it has virtually disappears by the age of 7 years. However the vessels in the ligamentum teres have developed between 4 and 7 years of age the femoral head may depend for its blood supply and venous drainage almost entirely on the lateral epiphyseal vessels whose situations in the retinacula makes them susceptible to stretching and to pressure from an effusion.
a. Damage to retinacular arteries causes avascular necrosis of the head, such as damage is maximal in subcapital fractures and least in basal fractures
b. More proximally the fracture located, the worse the prognosis
c. A few weeks later a nonocolloid scan may show diminished vascularity.
d. The changes of a vascular necrosis appears on X-rays generally 1-2 years after injuries. Common sites of avascular necrosis - # neck femur, # scaphoid # neck of talus, dislocation of the lunate bone, femoral condyles, head of the humerus, capitulum