Kennon Justin C, Lu Caroline, McGee-Lawrence Meghan E, Crosby Lynn A
Department of Orthopaedic Surgery, Medical College of Georgia at Augusta University, Augusta, GA, USA.
Department of Orthopaedic Surgery, Medical College of Georgia at Augusta University, Augusta, GA, USA.
J Shoulder Elbow Surg. 2017 Jun;26(6):1023-1030. doi: 10.1016/j.jse.2016.10.018. Epub 2017 Jan 26.
Reverse total shoulder arthroplasty (RTSA) is a viable treatment option for rotator cuff tear arthropathy but carries a complication risk of scapular fracture. We hypothesized that using screws above the central glenoid axis for metaglene fixation creates a stress riser contributing to increased scapula fracture incidence. Clinical type III scapular fracture incidence was determined with screw placement correlation: superior screw vs. screws placed exclusively below the glenoid midpoint. Cadaveric RTSA biomechanical modeling was employed to analyze scapular fractures.
We reviewed 318 single-surgeon single-implant RTSAs with screw correlation to identify type III scapular fractures. Seventeen cadaveric scapula specimens were matched for bone mineral density, metaglenes implanted, and fixation with 2 screw configurations: inferior screws alone (group 1) vs. inferior screws with one additional superior screw (group 2). Biomechanical load to failure was analyzed.
Of 206 patients, 9 (4.4%) from the superior screw group experienced scapula fractures (type III); 0 fractures (0/112; 0%) were identified in the inferior screw group. Biomechanically, superior screw constructs (group 2) demonstrated significantly (P < .05) lower load to failure (1077 N vs. 1970 N) compared with constructs with no superior screws (group 1). There was no significant age or bone mineral density discrepancy.
Clinical scapular fracture incidence significantly decreased (P < .05) for patients with no screws placed above the central cage compared with patients with superior metaglene screws. Biomechanical modeling demonstrates significant construct compromise when screws are used above the central cage, fracturing at nearly half the ultimate load of the inferior screw constructs. We recommend use of inferior screws, all positioned below the central glenoid axis, unless necessary to stabilize the metaglene construct.
反式全肩关节置换术（RTSA）是治疗肩袖撕裂性关节病的一种可行选择，但存在肩胛骨折的并发症风险。我们推测，在关节盂中央轴上方使用螺钉进行关节盂假体固定会产生应力集中，导致肩胛骨折发生率增加。通过螺钉置入相关性确定临床III型肩胛骨折发生率：上方螺钉与仅置于关节盂中点下方的螺钉。采用尸体RTSA生物力学模型分析肩胛骨折情况。
我们回顾了318例由单一外科医生使用单一植入物的RTSA病例，并进行螺钉相关性分析以确定III型肩胛骨折。17个尸体肩胛标本根据骨密度、植入关节盂假体以及采用两种螺钉配置进行固定进行匹配：仅使用下方螺钉（第1组）与下方螺钉加一枚上方螺钉（第2组）。分析生物力学失效载荷。
在206例患者中，上方螺钉组有9例（4.4%）发生肩胛骨折（III型）；下方螺钉组未发现骨折（0/112；0%）。生物力学方面，与无上方螺钉的结构（第1组）相比，上方螺钉结构（第2组）的失效载荷显著降低（P < 0.05）（1077 N对1970 N）。年龄或骨密度无显著差异。
与使用上方关节盂螺钉的患者相比，未在中央假体上方置入螺钉的患者临床肩胛骨折发生率显著降低（P < 0.05）。生物力学模型表明，在中央假体上方使用螺钉时结构明显受损，在下方螺钉结构的极限载荷近一半时发生断裂。我们建议，除非有必要稳定关节盂假体结构，否则应使用均位于关节盂中央轴下方的下方螺钉。
