MRI of the cartilaginous epiphysis of the femoral head in the piglet hip after ischemic damage.

MRI of the cartilaginous epiphysis (CE) of piglet femoral head was performed after ischemic damage to study the changes in the CE found on MRI and to correlate these changes with histologic findings. Avascular necrosis of the femoral head was induced with a suture ligature in nine piglets; one piglet was killed postoperatively on day 3 and on weeks 1, 2, 3, 4, 6, 7, and 8 (two piglets were killed on week 3). MRI of the ischemic and contralateral nonischemic hip joints were obtained with a 60-mm field of view (low resolution MRI). Biopsy cores of the femoral heads were imaged with a 15-mm field of view (high resolution MRI) and correlated with histologic sections. The CE for all operated hips, except for the 3-day postoperative specimen, showed evidence of ischemic changes on histologic assessment; the severity of damage increased with time. The MRI appearance of ischemic and nonischemic CE was clearly different by 2 weeks after the operation. No trilaminar signal pattern was evident in the high resolution T2-weighted (T2W) imaging of the ischemic CE from 2 weeks after the operation. In the 3- to 8-week postoperative specimens, focal areas of low signal intensity on high resolution T1-weighted (T1W) and T2W imaging corresponded to the areas of chondronecrosis found on histologic assessment. The regions of high signal intensity on T2W imaging corresponded to the areas of chondrocyte clusters with increased safranin-O staining. High resolution MRI can demonstrate changes in the CE associated with ischemic injury and may have a role in the assessment of the CE and its development after ischemic injury.