Is Stage 2 idiopathic osteonecrosis of the hip joint associated with version angles on imaging methods?

In this study, we aimed to investigate whether anatomical variations of acetabulum were associated to idiopathic osteonecrosis (ON) of the femoral head.

Between January 2014 and March 2020, a total of 46 patients (32 males, 14 females; mean age: 43 years; range, 18 to 66 years) who were diagnosed with unilateral or bilateral ON of the hip joint and 44 healthy age- and sex-matched controls (30 males, 14 females; mean age: 46 years; range, 18 to 79 years) with no signs of ON of the hip joint were retrospectively analyzed. For both groups, measurements were taken of the anatomic parameters, including the acetabular version angle (VA), the sharp angle (SA), and the center-edge angle (CEA) on anteroposterior pelvic radiographs and magnetic resonance imaging (MRI) scans.

The mean VA of both hips was found to be significantly smaller in Group 1 than in Group 2 on both MRI and X-ray (14.9±4.1 and 14.4±3.1 vs. 17.3±3.9 and 18.0±3.7, respectively; p=0.004, p<0.001). The mean SA of both hips was found to be significantly smaller in Group 1 than in Group 2 on both MRI and X-ray (39.0±2.9 and 38.9±2.8 vs. 41.6±3.9 and 40.8±4.9, respectively; p=0.001, p=0.036). The mean CEA of both hips was found to be significantly larger in ON group than in control group on both MRI and X-ray (36.7±6.1 and 36.9±7.0 vs. 32.0±6.0 and 31.5±7.5, respectively; p<0.001, p=0.001).

Version angles were found to be smaller in patients with ON and more acetabular coverage was observed. Greater coverage of the acetabulum may indicate early collapses of the femoral head even in Stage 2 ON patients. The smaller version angles may be associated with ON.