Risk factors for avascular necrosis of the femoral head:
(1) more severe dislocation, with Grade III or IV traumatic dislocation using the scheme of Stewart and Milford (see Chapter 29)
(2) delay in reduction of the dislocated joint > 6 hours from the time of the accident
where:
• Grade III dislocation involves a blast fracture of the acetabulum with disintegration of the acetabular rim.
• Grade IV dislocation involves fracture of the femoral head and/or neck.
• The rate of avascular necrosis was about 5% if the fracture was reduced within 6 hours, versus 53% with more than 6 hours.
Usual causes of a delay in hip reduction:
(1) failure to recognize the dislocation
(2) unsuccessful attempts at close reduction
(3) lack of proper radiographs (lateral view, post-reduction)
(4) delay in reaching the hospital
