Biphasic threat to femoral head perfusion in abduction: arterial hypoperfusion and venous congestion.

Overview

BACKGROUND: Hip abduction can cause avascular necrosis (AVN) of the femoral head in infants. OBJECTIVE: To compare the US perfusion pattern of femoral head cartilage in neutral position with that in different degrees and duration of abduction, testing the venous congestion theory of post-abduction ischemia. MATERIALS AND METHODS: In 20 neonates, the Doppler flow characteristics of the posterosuperior (PS) branch of the femoral head cartilage feeding vessels were evaluated in neutral and at 30 degrees, 45 degrees, and 60 degrees abduction. In three neonates the leg was held in 45-degree abduction and flow was assessed at 5, 10, and 15 min. RESULTS: Male/female ratio was 11/9 with a mean age of 1.86 +/- 0.7 weeks. The peak systolic velocities (PSV) declined in all three degrees of abduction. After 15 min of 45-degree abduction, the mean PSV declined and showed an absent or reversed diastolic component and undetectable venous return. No perfusion was detected at 60-degree abduction. CONCLUSION: Abduction-induced femoral head ischemia is biphasic and degree- and duration-dependent. In phase I there is arterial hypoperfusion and in phase II there is venous congestion. A new pathogeneses for femoral head ischemia is offered.