MR findings associated with positive distraction of the hip joint achieved by axial traction

To determine which MR-arthrography findings are associated with positive hip joint distraction.

One hundred patients with MR arthrography of the hip using axial traction were included. Traction was applied during the MR examination with an 8 kg (females) or 10 kg (males) water bag, attached to the ankle over a deflection pulley. Fifty patients showing joint space distraction were compared to an age- and gender-matched control group of 50 patients that did not show a joint distraction under axial traction. Two radiologists assessed the neck-shaft angle, lateral and anterior center-edge (CE) angles, CE angles in the transverse plane, extrusion index of the femoral head, acetabular depth, alpha angle, acetabular version, ligamentum teres, joint capsule and ligaments, iliopsoas tendon and the labrum.

Mean joint space distraction in the study group was 0.9 ± 0.6 mm. Patients with positive joint space distraction had significantly higher neck-shaft angles (control group 131.6 ± 5.4°/study group 134.1 ± 6.1°, p < 0.05), smaller lateral CE angles (38.1 ± 5.9°/34.6 ± 7.2°, p < 0.05), smaller overall transverse CE angles (161.4 ± 9.9°/153.6 ± 9.6°, p < 0.001), smaller acetabular depth (4.1 ± 2.4 mm/5.8 ± 2.5 mm, p < 0.01), higher alpha angles (53.5 ± 7.8°/59.2 ± 10.1°, p < 0.01) and a thicker ligamentum teres (4.7 ± 1.4 mm/5.4 ± 1.8 mm, p < 0.05). The other parameters revealed no significant differences. ICC values for interobserver agreement were 0.71-0.95 and kappa values 0.43-0.92.

Increased neck-shaft angles, small CE angles, small acetabular depth, higher alpha angles and a thick ligamentum teres are associated with positive joint distraction.