gms | German Medical Science

Objectives: The purpose of this study was to evaluate the effects of anterior necrotic lesion on the femoral head collapse in non-collapsed osteonecrosis of the femoral head (ONFH).

Methods: We reviewed consecutive 116 hips in 99 non-collapsed ONFH patients with the follow-up for at least 2 years (average 4.6 years, 2.0-11.8) who had undergone both coronal and oblique views of magnetic resonance (MR) imaging before collapse. The presence or absence of collapse was investigated using every follow-up radiographs. According to the classification system of the Japanese Investigation Committee of Health and Welfare, 14 hips were classified as type A, indicating the presence of a necrotic lesion occupying one-third of the weight-bearing portion; 33 hips were classified as type B, indicating the presence of a necrotic lesion occupying one-third to two-thirds of the weight-bearing portion; 69 hips were type C, indicating the presence of a necrotic lesion occupying more than two-thirds of the weight-bearing portion or extending to the acetabular edge. The anterior boundary of the necrotic lesion was assessed by anterior necrotic angle on mid-slice oblique view of MR imaging before collapse (Fig). The following factors were statistically analyzed between hips with or without collapse: age, sex, BMI, stage, type, etiology of ONFH, follow-up period and radiological parameters (maximum depth of necrotic lesion, volume of necrotic lesion and anterior necrotic angle).

Results and Conclusion: Femoral head collapse was confirmed in 61 hips (52.6%) during a mean period of 13.8 months (2-50 months) after MR imaging. The survival rate in type A, B and C was 100%, 77% and 16%, respectively. There were significant differences in sex, type, etiology of ONFH, follow-up period and all radiological parameters between hips with or without collapse. In type-B ONFH, anterior necrotic angle were significantly associated with femoral head collapse based on univariate analysis (Table 1). In type-C ONFH, both BMI and anterior necrotic angle were significantly associated with femoral head collapse based on univariate analysis (Table 2). In both type-B and type-C ONFH, multivariate analysis revealed that the anterior necrotic angle was independently associated with femoral head collapse, respectively.

The results of our study suggest that the anterior boundary of the necrotic lesion is significant prognostic factor of femoral head collapse.