GADOLINIUM-ENHANCED MR-IMAGING DEMONSTRATES ABDUCTION-CAUSED HIP ISCHEMIA AND ITS REVERSAL IN PIGLETS

Purpose. To determine whether gadolinium-enhanced MR imaging can detect early reversible ischemia of the capital femoral epiphysis and physis induced by hip hyperabduction in piglets. Materials and methods. Thirteen 1- to 3-week-old piglets were placed in maximal abduction of both hips and studied with dynamic gadolinium-enhanced MR imaging 1-6 h later to assess ischemia of the 26 femoral heads. They were then allowed to ambulate freely for 1 or 7 days, and reimaged in neutral position to assess reperfusion. Enhancement was evaluated on MR images and compared with histologic findings. Results. Ischemia after hyperabduction developed in all 26 cartilaginous epiphyses and in 85% of the physes. The most frequent abnormality was a sharply marginated nonenhancing area in the anterior part of the femoral head. A smaller area of ischemia developed in the posterior part of the femoral head, adjacent to the acetabular rim. The secondary center of ossification was ischemic in 56% of the hips after 1 h of abduction and in all hips after 4 or 6 h (p=0.02). The overall severity of ischemia was greater with increasing abduction time (p<0.001) and increasing degree of abduction (p<0.01). There was partial reperfusion in 83% of the hips after 1 day of ambulation and complete reperfusion in all 26 hips (100%) after 1 week. Conclusion. Enhanced MRI detects early ischemia of the epiphyseal and physeal cartilage and the epiphyseal marrow. In piglets, ischemia due to hyperabduction is reversible if corrected within 6 h.