Gadolinium-enhanced MR imaging demonstrates abduction-caused hip ischemia and its reversal in piglets.

Abstract

To determine if gadolinium-enhanced MR imaging can detect early reversible ischemia of the capital femoral epiphysis and physis induced by hip hyperabduction in piglets. Thirteen 1- to 3-week-old piglets were placed in maximal bilateral hip abduction and then studied with dynamic gadolinium-enhanced MR imaging 1-6 hr later to assess ischemia of the 26 femoral heads. The piglets were then allowed to ambulate freely for 1 or 7 days and reimaged in neutral position to assess reperfusion. We evaluated enhancement on MR images and compared them with histologic findings. Decreased or absent enhancement, interpreted as ischemia, developed after maximal hip abduction in all 26 cartilaginous epiphyses and 85% of the 26 physes. The most frequently seen abnormality was a sharply marginated, nonenhancing area in the anterior part of the femoral head. A smaller area of decreased enhancement developed in the posterior part of the femoral head adjacent to the acetabular rim. The secondary center of ossification was ischemic in 10 (56%) of the 18 hips after 1 hr of abduction and in all 8 hips after 4 or 6 hr (p = .02). The overall severity of ischemia was greater with longer abduction times (p < .001) and greater degrees of abduction (p < .01). Reperfusion was complete in two (17%) of the 12 hips after 1 day of ambulation and in all 10 (100%) after 1 week of ambulation. Enhanced MR imaging detects early ischemia of the epiphyseal and physeal cartilage and the epiphyseal marrow. In piglets, ischemia due to maximal abduction is reversible if corrected within 6 hr.