Department of Mechanical Engineering, The University of Melbourne, Parkville, Victoria, Australia.
J Bone Joint Surg Am. 2010 May;92(5):1221-30. doi: 10.2106/JBJS.I.00001.
Reverse total shoulder arthroplasty is known to increase the moment arm of the middle subregion of the deltoid during shoulder abduction; however, at present, comprehensive data regarding the shoulder muscle moment arm through the full range of abduction and flexion are not available. The purpose of this study was twofold: (1) to measure the instantaneous moment arms of thirteen subregions of major muscles spanning the glenohumeral joint during abduction and flexion of the shoulder after reverse total shoulder arthroplasty and (2) to compare these data with the muscle moment arms previously measured preoperatively in the anatomical shoulders.
Reverse total shoulder arthroplasty was performed on eight entire cadaveric upper extremities. The specimens were mounted onto a dynamic testing apparatus, and the instantaneous abductor/adductor and flexor/extensor moment arms of subregions of the deltoid, latissimus dorsi, pectoralis major, teres major, and subscapularis muscles (a total of thirteen subregions) were measured with use of the tendon excursion method. These muscle moment arms were compared with those measured preoperatively in the anatomical shoulders.
Reverse total shoulder arthroplasty resulted in significant increases in the abductor moment arms of the anterior subregion of the deltoid (mean increase = 10.4 mm; 95% confidence interval = 7.5 to 13.3 mm) and the middle subregion of the deltoid (mean increase = 15.5 mm; 95% confidence interval = 10.8 to 20.3 mm) as well as recruitment of the posterior subregion of the deltoid as an abductor. The superior subregion of the pectoralis major (the clavicular fibers) and anterior subregion of the deltoid were the most effective flexors and had a substantial potential to initiate flexion. The adductor and extensor moment arms of the teres major, latissimus dorsi subregions, and inferior and middle subregions of the pectoralis major increased substantially after the arthroplasty. The subscapularis subregions behaved as extensors, abductors, and adductors after the arthroplasty; this was in contrast to their roles in the anatomical shoulder, in which they were mainly flexors and adductors.
Reverse total shoulder arthroplasty increases the moment arms of the major abductors, flexors, adductors, and extensors of the glenohumeral joint, thereby reducing muscle effort during common tasks such as lifting and pushing.
反向全肩关节置换术已知在肩关节外展过程中增加三角肌中部亚区的力臂；然而，目前，关于肩关节全范围外展和屈曲时肩部肌肉力臂的综合数据尚不清楚。本研究的目的有两个：(1)测量反向全肩关节置换术后肩关节外展和屈曲时跨越盂肱关节的 13 个主要肌肉亚区的瞬时力臂；(2)将这些数据与术前解剖肩部测量的肌肉力臂进行比较。
对 8 个完整的尸体上肢进行反向全肩关节置换术。标本安装在动态测试装置上，使用肌腱位移法测量三角肌、背阔肌、胸大肌、大圆肌和肩胛下肌的 13 个亚区的外展肌/内收肌和屈肌/伸肌的瞬时力臂。将这些肌肉力臂与术前解剖肩部测量的力臂进行比较。
反向全肩关节置换术后，三角肌前亚区的外展力臂显著增加（平均增加 10.4mm；95%置信区间 7.5 至 13.3mm）和三角肌中亚区的力臂（平均增加 15.5mm；95%置信区间 10.8 至 20.3mm）以及三角肌后亚区作为外展肌的募集。胸大肌的上亚区（锁骨纤维）和三角肌前亚区是最有效的屈肌，具有很大的起始屈曲潜力。三角肌后亚区、背阔肌亚区、胸大肌下亚区和中亚区的内收肌和伸肌力臂在关节置换后显著增加。肩胛下肌亚区在关节置换后表现为伸肌、外展肌和内收肌；这与它们在解剖肩部的作用形成对比，在解剖肩部，它们主要是屈肌和内收肌。
反向全肩关节置换术增加了盂肱关节的主要外展肌、屈肌、内收肌和伸肌的力臂，从而减少了在举升和推动等常见任务中肌肉的用力。
