• Yusuke Kubo, Goro Motomura, Satoshi Ikemura, Kazuhiko Sonoda, Takuaki Yamamoto, and Yasuharu Nakashima.
• Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.
• Arch Orthop Trauma Surg. 2017 Jul 1; 137 (7): 933-938.

IntroductionThe 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 MethodsFrom 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).ResultsThe 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 < 0.0001). These parameters had a positive association with the depth of femoral head collapse (p < 0.0001 and p < 0.01, respectively). However, there were no significant differences in either the α-angle or HNOR between hips with ONFH before collapse and hips without ONFH.ConclusionsThis study demonstrated that the decreased femoral head-neck offset observed in patients with ONFH was a consequence of collapse.

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