Bone marrow lesion on magneticresonance imaging indicates the last chance for hip osteonecrosis treated with vascularized fibular grafting before collapse.

Abstract

Timing of surgery is the most critical prognostic factor for hip osteonecrosis treated with free vascularized fibular grafting (FVFG). Bone marrow lesion (BML) on MRI usually occurs immediately before femoral head collapse. We conducted a retrospective cohort study to evaluate whether the noncollapsed hips with BML can benefit from FVFG. Consecutive patients undergoing modified FVFG were identified from our clinical repository between January 2014 and December 2014. Based on whether BML was pre-operatively detected, the four year radiographic and clinical outcomes were compared. In the BML cohort, 22 of 53 hips (42%) showed radiographic signs of osteonecrosis progression, which was significantly higher than that in the control cohort (8 of 49, 16%; P = 0.005). The BML hips showed a significantly lower pre-operative Harris Hip Score (HHS) than those without BML (77.8 vs. 85.5, P = 0.046), whereas no such difference was observed in the final HHS or its post-operative improvement (HHS 90 vs. 94, P = 0.397; HHS improvement 12 vs. 8, P = 0.067). In the subgroup of patients with a pre-operative HHS lower than 80, BML hips were associated with a slightly lower final HHS than hips without BML. Four of 5 (80%) failed hips with BML had a poor pre-operative hip function. BML indicates the last chance for a reproducible improvement in the treatment of hip osteonecrosis with FVFG before collapse. However, the concomitant lower pre-operative HHS (< 80) is a poor prognostic factor for BML-positive hips.