Effects of non-weight-bearing on the immature femoral head following ischemic osteonecrosis: An experimental investigation in immature pigs

Background: Local non-weight-bearing as a treatment for Legg-Calvé-Perthes disease remains controversial since a clear scientific basis for this treatment is lacking. The purpose of this study was to determine the effects of non-weight-bearing on decreasing the femoral head deformity following ischemic osteonecrosis and to investigate its biological effects. Methods: Unilateral femoral head ischemia was induced in sixteen piglets by placing a ligature around the femoral neck and transecting the ligamentum teres. Eight animals received a hind-limb amputation to prevent weight-bearing on the ischemic side (NWB group). The remaining eight piglets were allowed to bear weight as tolerated (WB group). The contralateral femoral heads of the WB group were used as normal controls. All animals were killed at eight weeks after induction of ischemia, when a deformity is expected in this model. Radiographic, microcomputed tomographic (micro-CT), and histomorphometric assessments were performed. Results: Radiographic and micro-CT assessments showed significantly greater flattening of the infarcted epiphysis in the WB group compared with the NWB group. Themean epiphyseal quotient (ratio of femoral head height to diameter) was significantly lower in the WB group (0.29 ± 0.06) compared with the NWB group (0.41 ± 0.06, p < 0.001). Histomorphometric analyses showed that themean percentage revascularization of the infarcted epiphysis was significantly greater in the NWB group (95% ± 14%) compared with the WB group (34% ± 33%, p < 0.0004), suggesting that revascularization was more rapid in the NWB group. Both histomorphometric and micro-CT analyses of trabecular bone parameters showed significantly decreased bone volume and decreased trabecular number in the infarcted epiphysis of the NWB group compared with theWB group (p < 0.05). Conclusions: Local non-weight-bearing decreased the deformity following ischemic femoral head osteonecrosis and increased the rates of revascularization and resorption of the infarcted epiphysis. Clinical Relevance: Local non-weight-bearing was mechanically protective but biologically suboptimal following ischemic osteonecrosis since it increased the imbalance of bone resorption and formation.