This study indicates that ONFH patients with anterior localization of a necrotic lesion can develop collapse even if the necrotic lesion is medially located.

Our results will clarify the pathogenic mechanism of collapse in ONFH. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Objectives To quantify the volume of bone-resorptive lesions in post-collapse osteonecrosis of the femoral head (ONFH) using micro-computed tomography (micro-CT) and assess their characteristics in postcollapse ONFH.Methods We investigated 35 femoral heads resected from 35 patients with ONFH (20 men and 15 women; mean age, 47.2 years). On each of seven coronal high-resolution micro-CT slices of the femoral head, the bone-resorptive areas were extracted using bone microstructure measurement software. Next, the total bone-resorptive volume ratio, defined as the ratio of all bone-resorptive cross-sectional areas to all femoral head cross-sectional areas in all seven slices, was calculated. Associations between total boneresorptive volume ratio and sex, age, ONFH-associated factors, patient workload levels, ONFH stage, ONFH type, necrotic volume on magnetic resonance imaging, and duration from the onset of pain to surgery were analyzed. Lesion location and the association between bone-resorptive lesion and collapse were also evaluated.Results The mean total bone-resorptive volume ratio was 7.0 ± 6.0%, which varied significantly by ONFH stage (ARCO collapse quantitation 3A, 3.5 ± 2.1%; 3B, 6.8 ± 3.0%; and 3 C, 13.6 ± 8.8%). ONFH stage was independently associated with total bone-resorptive volume ratio (P < 0.05). Furthermore, high boneresorptive volume ratios were found in the anterior femoral head and were associated with collapse.Conclusions This study demonstrated that bone-resorptive volume in post-collapse ONFH was significantly associated with the disease stage, which was more widespread in the anterior portion of the femoral head than in the posterior portion.

The purpose of this study was to assess the differences in magnetic resonance (MR) findings between the symptomatic and asymptomatic pre-collapse stage of osteonecrosis of the femoral head (ONFH). Materials and methods: This study reviewed 123 consecutive hips in 91 patients in the pre-collapse stage of ONFH based on plain radiographic findings. These 123 hips were divided into symptomatic and asymptomatic groups according to the pain domain score in the Harris hip score system. Bone marrow edema (BME), synovial fluid effusion, and subchondral fracture were evaluated using MR imaging. Odds ratios (ORs) were calculated between these three parameters and symptoms. The subsequent clinical course after MR examination was also assessed for each hip that could be followed more than 1 year. Results: Forty-six hips (37.4%) were categorized as symptomatic and 77 hips (62.6%) as asymptomatic. The prevalence of BME, synovial fluid effusion, and subchondral fracture were 87.0% (40/46), 80.4% (37/46), and 34.8% (16/46), respectively, in the symptomatic group, and 0%, 28.6% (22/77), and 0%, respectively, in the asymptomatic group, indicating significant differences between the two groups (p < 0.0001). Among these parameters, BME showed the highest OR with regard to the presence or absence of symptoms (BME, 965.8; joint effusion, 10.3; subchondral fracture, 83.9). Due to persistent pain and subsequent collapse, 30 of 35 (85.7%) symptomatic hips with BME subsequently underwent surgical treatment at a mean interval of 3.47 months after MR examination, while 25 of 66 (37.9%) asymptomatic hips without BME underwent surgical treatment at a mean interval of 20.7 months after MR examination. Conclusions: This study demonstrated that symptomatic pre-collapse ONFH diagnosed based on plain radiographic findings could be distinguished from asymptomatic pre-collapse ONFH by the presence of BME on MR imaging, and thus BME may be a sign of occult fracture.

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