PURPOSE Literature describes the concern of an overstuffed shoulder joint after a resurfacing humeral head implant (RHHI). The purpose of this study was to evaluate inter-observer variability of (1) the critical shoulder angle (CSA), (2) the length of the gleno-humeral offset (LGHO), and (3) the anatomic center of rotation (COR) in a patient population operated with a Global Conservative Anatomic Prosthesis (CAP) RHHI. The measurements were compared between the revision and non-revision groups to find predictive indicators for failure. METHODS Pre- and postoperative radiographs were retrieved from 48 patients who underwent RHHI from 2007 to 2009 using a Global CAP hemiarthroplasty for end-stage osteoarthritis. This cohort consisted of 36 females (12 men) with a mean age of 77 years (SD 7.5). Two musculoskeletal radiologist and two specialized shoulder orthopedic surgeons measured the CSA, LGHO, and COR of all patients. RESULTS The inter-observer reliability showed excellent reliability for the CSA, LGHO, and the COR, varying between 0.91 and 0.98. The mean COR of the non-revision group was 4.9 mm (SD 2.5) compared to mean COR of the revision group, 8 mm (SD 2.2) (p < 0.01). The COR is the predictor of failure (OR 1.90 (95%Cl 1.19-3.02)) with a cut of point of 5.8 mm. The mean CSA was 29.8° (SD 3.9) There was no significant difference between the revision and non-revision groups (p = 0.34). The mean LGHO was 2.6 mm (SD 3.3) post-surgery. The mean LGHO of the revision group was 3.9 (SD 1.7) (p = 0.04) post-surgery. Despite the difference in mean LGHO, this is not a predictor for failure. CONCLUSION The CSA, LGHO, and COR can be used on radiographs and have a high inter-observer agreement. In contrast with the CSA and LGHO, we found a correlation between clinical failure and revision surgery in case of a deviation of the COR greater than 5 mm. TRIAL REGISTRATION Institutional review board, number: ACLU 2016.0054, Ethical Committee number: CBP M1330348. Registered 7 November 2006.

中文翻译：

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半关节置换术中过度填充是失败的潜在风险。

目的 文献描述了肱骨头植入物 (RHHI) 表面置换后肩关节过度充填的问题。本研究的目的是评估观察者之间的变异性：(1) 临界肩角 (CSA)、(2) 盂肱关节偏移长度 (LGHO) 和 (3) 解剖旋转中心 (COR) ）在使用全局保守解剖假体 (CAP) RHHI 进行手术的患者群体中。对修正组和非修正组之间的测量结果进行比较，以找到失败的预测指标。方法 检索 48 名 2007 年至 2009 年间接受 RHHI 治疗的终末期骨关节炎患者的术前和术后 X 线照片，这些患者使用 Global CAP 半关节置换术。该队列由 36 名女性（12 名男性）组成，平均年龄为 77 岁（SD 7.5）。两名肌肉骨骼放射科医生和两名专业肩部整形外科医生测量了所有患者的 CSA、LGHO 和 COR。结果 CSA、LGHO 和 COR 的观察者间可靠性表现出优异的可靠性，在 0.91 和 0.98 之间变化。未修复组的平均 COR 为 4.9 mm (SD 2.5)，而修复组的平均 COR 为 8 mm (SD 2.2) (p < 0.01)。COR 是失效的预测因子（OR 1.90 (95%Cl 1.19-3.02)），切割点为 5.8 mm。平均 CSA 为 29.8° (SD 3.9) 翻修组和非翻修组之间没有显着差异 (p = 0.34)。术后平均 LGHO 为 2.6 mm (SD 3.3)。修复组术后平均 LGHO 为 3.9 (SD 1.7) (p = 0.04)。尽管平均 LGHO 存在差异，但这并不能预测失败。结论 CSA、LGHO 和 COR 可用于 X 线照片，并且具有较高的观察者间一致性。与 CSA 和 LGHO 相比，我们发现当 COR 偏差大于 5 mm 时，临床失败与翻修手术之间存在相关性。试验注册机构审查委员会，编号：ACLU 2016.0054，伦理委员会编号：CBP M1330348。2006 年 11 月 7 日注册。