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

Abstract

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

Patients and methods: 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.

Results: 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).

Conclusion: 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.

Figure 1. Axial MRI image (T1 image). Version angle on MRI is between Lines 2 and 3. Line 1: Inter-ischial line; Line 2: It is vertical to the Line 1; Line 3: It is connecting the anterior and posterior bony edges of the acetabular rim. MRI: Magnetic resonance imaging.

Figure 2. Anteroposterior pelvic radiography. Line 1: Inter-ischial line; Line 2: It is drawn from the inferolateral part of the tear drop to the margin of the lateral acetabulum; Line 3: Same as Line 2; Line 4: It is drawn from the most lateral margin of the acetabulum to the most sclerotic part of the posterior lunate fossa of the acetabulum. Version angle (VA) on X-ray image: The angle is between Line 3 and Line 4. Sharp angle (SA): The angle is between Line 1 and Line 2.

Figure 3. Magnetic resonance imaging coronal image (T1 image). Line 1: Inter-ischial line; Line 2: It is drawn from the inferolateral part of the tear drop to the edge of the lateral acetabular sourcil; Line 3: It is vertical to the center of the femoral head; Line 4: It is drawn from the center of the femoral head to the lateral margin of the acetabular edge; Number 5: A circle which best fits on the femoral head. Sharp angle (SA) on magnetic resonance imaging (MRI): The angle between Lines 1 and 2. Center-edge angle (CEA) on MRI is formed between Lines 3 and 4.

Figure 4. Anteroposterior pelvic radiography. Line 1: It is vertical to the center of the femoral head; Line 2 is drawn from the center of the femoral head to the lateral margin of the acetabular rim; Number 3: A circle which best fits on the femoral head. Center-edge angle (CEA) on pelvic radiography: The angle between Lines 1 and 2.