Repair in osteonecrosis of the femoral head: MR imaging features at long-term follow-up.

The purpose of this study was to evaluate retrospectively the progression of reparative changes in osteonecrosis of the femoral head over a long period of time, using both serial plain films and magnetic resonance (MR) images. The subjects were 25 patients with 33 hips affected by osteonecrosis, followed conservatively for more than 10 years (mean, 14.1; range, 10 to 23.4). At the latest follow-up examination, there were 11 hips at the non-collapse stage, 17 hips at the collapse stage where collapse has ceased, and five hips at the osteoarthritic stage. An increase in radiographic sclerosis of the lesion area was seen in 14 of 17 hips which showed cessation of collapse, 13 of which showed an intralesional area with intermediate signal intensity on fat suppression MR images. Four of five hips at the osteoarthritic stage also showed an intralesional area with intermediate signal intensity on fat suppression MR images. Ten of 11 hips at the non-collapse stage showed a normal fat signal intensity area demarcated with a low-signal-intensity band on T1-weighted MR images. In the 24 hips followed for more than 5 years with MR imaging (mean, 9.2; range, 5.9 to 13.8), changes of lesion size of abnormal signal intensity on T1-weighted MR images were not observed. In conclusion, reparative process was limited to the periphery of osteonecrosis over a long period of time unless collapse had occurred. If collapse had ceased minimally, the reconstructive repair process could be facilitated.