Effect of collapse on the deformity of the femoral head–neck junction in osteonecrosis of the femoral head

Introduction The purpose of this study was to morphologically assess the effect of collapse on the deformity of the femoral head–neck junction in patients with nontraumatic osteonecrosis of the femoral head (ONFH). Materials and methods From January 2005 through March 2016, magnetic resonance (MR) imaging including the oblique view was repeatedly performed before and after collapse in 24 hips of patients with ONFH (16 men, 8 women; mean age 43 years; range 23–68 years), that were the subjects of this study. The interval of MR imaging before and after collapse was 8.0 months (range 1–32 months). In addition, 82 asymptomatic hips in patients without ONFH as identified by MR imaging taken at the same duration were used as controls. The oblique MR image was used to measure the radiological parameters of the femoral head–neck junction, including the α-angle and head–neck offset ratio (HNOR). Results The α-angle and HNOR after collapse (58.3° ± 10.0° and 0.138 ± 0.033, respectively) indicated significantly decreased anterior femoral head–neck offset compared with those before collapse (46.2° ± 5.7° and 0.178 ± 0.018, respectively; p