Roche Christopher P, Hamilton Matthew A, Diep Phong, Flurin Pierre-Henri, Routman Howard D
Bull Hosp Jt Dis (2013). 2013;71 Suppl 2:S18-24.
A computer model quantified and compared muscle lengths and moment arms of two different reverse shoulder arthroplasty humeral tray designs during two different motions.
The computer model simulated internal/ external rotation and abduction in the scapular plane for the normal shoulder, the 38 mm non-offset, and the 38 mm posterior-superior offset reverse shoulders. Muscle lengths were directly measured for seven muscles during each motion. External rotation moment arms were calculated for five muscles during each motion.
The offset tray shifted the humerus posteriorly and superiorly relative to the non-offset tray. The more superior humeral position with the offset tray elongated the deltoid 1.0% to 3.8% less and caused each muscle to convert from an adductor to abductor earlier in abduction. The more posterior humeral position with the offset tray better restored the anatomic muscle tension, decreased the internal rotation capability (e.g., moment arm) of the subscapularis and teres major by 7.1 mm and 9.5 mm, and increased the external rotation capability of the posterior deltoid, infraspinatus, and teres minor by 1.3 mm, 8.6 mm, and 7.8 mm.
The offset humeral tray bet- ter restored the anatomic muscle tensioning and increased the external rotation moment arms relative to the non-offset humeral tray, which has positive implications on strength, stability, and motion.
一个计算机模型对两种不同的反向肩关节置换肱骨头假体设计在两种不同运动过程中的肌肉长度和力臂进行了量化和比较。
该计算机模型模拟了正常肩关节、38毫米无偏移和38毫米后上偏移反向肩关节在肩胛平面内的内/外旋转和外展。在每个运动过程中直接测量七块肌肉的长度。在每个运动过程中计算五块肌肉的外旋力臂。
偏移假体相对于无偏移假体使肱骨向后上方移位。偏移假体使肱骨处于更高位置，使三角肌长度缩短1.0%至3.8%，并使每块肌肉在外展过程中更早地从内收肌转变为外展肌。偏移假体使肱骨处于更靠后的位置，能更好地恢复解剖学上的肌肉张力，使肩胛下肌和大圆肌的内旋能力（如力臂）分别降低7.1毫米和9.5毫米，使后三角肌、冈下肌和小圆肌的外旋能力分别增加1.3毫米、8.6毫米和7.8毫米。
相对于无偏移肱骨头假体，偏移肱骨头假体能更好地恢复解剖学上的肌肉张力，并增加外旋力臂，这对力量、稳定性和运动具有积极意义。
