Load-bearing capacity of the bone structures of anterolateral weight-bearing area plays an important role in the progressive collapse in osteonecrosis of the femoral head (ONFH). The purpose of this study is to assess the efficacy of combined evaluation of anteroposterior (AP) and frog-leg lateral (FLL) view in diagnosing collapse. Between December 2016 and August 2018, a total of 478 hips from 372 patients with ONFH (268 male, 104 female; mean age 37.9 ± 11.4 years) were retrospectively evaluated. All patients received standard AP and FLL views of hip joints. Japanese Investigation Committee (JIC) classification system was used to classify necrotic lesion in AP view. Anterior necrotic lesion was evaluated by FLL view. All patients with pre-collapse ONFH underwent non-operative hip-preserving therapy. The collapse rates were calculated and compared with Kaplan–Meier survival analysis with radiological collapse as endpoints. Forty-four (44/478, 9.2%) hips were classified as type A, 65 (65/478, 13.6%) as type B, 232 (232/478, 48.5%) as type C1 and 137 (137/478, 28.7%) as type C2. Three hundred cases (300/478, 62.5%) were collapsed at the initial time point. Two hundred and twenty six (226/300, 75.3%) hips and 298 (298/300, 99.3%) hips collapse were identified with AP view and FLL view, respectively. An average follow-up of 37.0 ± 32.0 months was conducted to evaluate the occurrence of collapse in 178 pre-collapse hips. Collapses occurred in 89 hips (50.0%). Seventy-seven (77/89, 86.5%) hips were determined with AP view alone and 85 (85/89, 95.5%) hips were determined with the combination of AP and FLL views. The collapse rates at five years were reported as 0% and 0%, 16.2% and 24.3%, 58.3% and 68.1% and 100% and 100% according to AP view alone or combination of AP and FLL views for types A, B, C1 and C2, respectively. The collapse can be diagnosed more accurately by combination of AP and FLL views. Besides, JIC type A and type B ONFH can be treated with conservative hip preservation, but pre-collapse type C2 ONFH should be treated with joint-preserving surgery. Type C1 needs further study to determine which subtype has potential risk of collapse.

中文翻译：

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结合蛙腿侧视图可以作为更敏感的 X 射线位置监测股骨头坏死塌陷

前外侧负重区骨结构的承载能力在股骨头坏死（ONFH）的进行性塌陷中起重要作用。本研究的目的是评估前后位 (AP) 和蛙腿外侧 (FLL) 视图联合评估在诊断塌陷中的有效性。在 2016 年 12 月至 2018 年 8 月期间，回顾性评估了 372 名 ONFH 患者（268 名男性，104 名女性；平均年龄 37.9 ± 11.4 岁）的 478 个髋关节。所有患者均接受标准的髋关节 AP 和 FLL 视图。日本调查委员会 (JIC) 分类系统用于在 AP 视图中对坏死病变进行分类。通过 FLL 视图评估前部坏死病变。所有塌陷前 ONFH 患者均接受了非手术保髋治疗。计算塌陷率并与以放射塌陷为终点的 Kaplan-Meier 生存分析进行比较。44 (44/478, 9.2%) 髋为 A 型，65 (65/478, 13.6%) 为 B 型，232 (232/478, 48.5%) 为 C1 型和 137 (137/478, 28.7%) 为 C2 型。300 例 (300/478, 62.5%) 在初始时间点塌陷。AP视图和FLL视图分别确定了226个（226/300，75.3％）髋和298个（298/300，99.3％）髋塌陷。平均随访 37.0 ± 32.0 个月，以评估 178 例塌陷前髋部塌陷的发生情况。89 髋 (50.0%) 发生塌陷。77 个 (77/89, 86.5%) 髋关节由 AP 视图单独确定，85 个 (85/89, 95.5%) 髋关节由 AP 和 FLL 视图组合确定。根据单独的 AP 视图或 A、B 类型的 AP 和 FLL 视图的组合，五年的崩溃率报告为 0% 和 0%、16.2% 和 24.3%、58.3% 和 68.1% 以及 100% 和 100%，分别为 C1 和 C2。结合 AP 和 FLL 视图可以更准确地诊断塌陷。此外，JIC A 型和 B 型 ONFH 可采用保守保髋治疗，塌陷前 C2 型 ONFH 应采用保关节手术治疗。C1 型需要进一步研究以确定哪个亚型具有潜在的崩溃风险。JIC A型和B型ONFH可采用保守保髋治疗，塌陷前C2型ONFH应采用保关节手术治疗。C1 型需要进一步研究以确定哪个亚型具有潜在的崩溃风险。JIC A型和B型ONFH可采用保守保髋治疗，塌陷前C2型ONFH应采用保关节手术治疗。C1 型需要进一步研究以确定哪个亚型具有潜在的崩溃风险。