Background Although several morphological abnormalities or variances of the hip joint have been proposed to be associated with hip joint degeneration, few studies have investigated any radiological features in patients with transient osteoporosis of the hip (TOH). The purpose of this study is to evaluate the morphological variances of the hip joint in TOH patients radiographically. Methods The TOH group consisted of 31 hips in 31 patients. Age- and gender-matched asymptomatic hips in patients with unilateral osteonecrosis of the femoral head were served as controls. Radiographs and MRI were utilized to examine the following parameters: acetabular dysplasia, acetabular overcoverage, acetabular retroversion, and asphericity of the femoral head–neck junction. Also, localization of the main bone marrow edema (BME) lesion was investigated. Results TOH patients had a significantly higher incidence of acetabular retroversion (52% with a positive cross-over sign and 29% with posterior wall deficiency) than the controls (13%, P = 0.0023; 6%, P = 0.043, respectively), which was also confirmed by smaller acetabular anteversion angles on axial MRI. In addition, TOH patients tended to show asphericity of the anterior femoral head–neck junction compared to controls (39% vs. 13%, P = 0.040). In 90% of the TOH patients, the main BME lesion was located in the subchondral area of the superior portion of the femoral head, and 77% of the lesion were recognized as a band-like pattern in MRI. Conclusions Acetabular retroversion and asphericity of the femoral head–neck junction were more commonly observed in TOH patients compared to controls. The main BME lesion was most frequently located in the superior portion of the femoral head.
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