Normal and ischemic epiphysis of the femur: diffusion MR imaging study in piglets

To evaluate normal diffusion characteristics in the femur in piglets and changes in diffusion with increasing duration of femoral head ischemia.

Normal epiphyses, physes, and metaphyses of piglets were evaluated with line-scan diffusion imaging (n = 12) and diffusion-tensor imaging (n = 4). Apparent diffusion coefficient (ADC) differences between normal proximal and distal femoral structures, epiphyseal and physeal cartilage, and epiphyseal and metaphyseal marrow were compared (Mann-Whitney test). Short-term femoral ischemia was investigated after maximal abduction of the hips for 3 hours (n = 6); ADCs before and after abduction were compared (Wilcoxon signed rank test). Prolonged ischemia was investigated with placement of a ligature around the neck of a femur (n = 7); the ADC of the femur in this condition was compared (Wilcoxon signed rank test) with that of the normal contralateral femur. Changes in ADC ratios at three durations of ischemia (Kruskal-Wallis test) were compared.

ADC was greater in epiphyseal cartilage (mean +/- 1 SD, 1.62 x 10(-3) mm2/sec +/- 0.38) than it was in physeal cartilage (1.28 x 10(-3) mm2/sec +/- 0.31) (P <.007) and greater in epiphyseal marrow (1.26 x 10(-3) mm2/sec +/- 0.38) than it was in metaphyseal marrow (0.91 x 10(-3) mm2/sec +/- 0.35) (P <.001). There was columnar arrangement of tensors in the physis. ADC decreased 26% after 3 hours of maximal abduction. After femoral neck ligature, ADC increased a mean of 27% after 6 hours and a mean of 75% after 96 hours.

Normal line-scan diffusion imaging findings indicate relative restriction of diffusion in the metaphysis and parallel orientation of tensors in the physis. Diffusion is initially restricted with decreased blood flow but increases if ischemia lasts longer.