ABSTRACT
BACKGROUND:Mechanical stress plays an important role in the progressive collapse in osteonecrosis of the femoral head.Therefore,the bone structure of weight-bearing area may be the risk factor for collapse.OBJECTIVE:To investigate the relationship between the bone preservation of weight-bearing area and collapse progression in necrotic femoral head.METHODS:Eighty-seven patients (102 hips) with ARCO stage Ⅱ osteonecrosis of the femoral head,diagnosed by MRI,were enrolled.All patients underwent a natural progression.Collapse and bone involvement of the weight-bearing area were viewed by anteroposterior and frog-leg lateral radiographs.According to the location of the necrotic lesion on the anterolateral portion of the femoral head,the necrosis was divided into three types:type 1,the posteromedial and central portions;type 2,part of the anterolateral portion;type 3,the entire anterolateral portion.The collapse rate and the time to collapse in different types were assessed.RESULTS AND CONCLUSION:(1) All patients were followed up for 3-58 months.(2) Of the 60 hips with collapse,46 (76.7％) hip collapse was identified on anteroposterior radiograph.On frog-leg lateral radiograph showing collapsed femoral head could be identified in 57 (95.0％) hips,which was significantly different (P ＜ 0.01).(3) In all 102 hips,the collapse rate in type 3 osteonecrosis of the femoral head was significantly higher than that of type 2 osteonecrosis of the femoral head (P ＜ 0.001),and the time to collapse was markedly shortened.None collapse occurred in all six hips with type Ⅰ osteonecrosis of the femoral head during follow-up.(4) In summary,preservation of anterolateral portion is associated with potential collapse progression in necrotic femoral head.