Department of Orthopedics and Rehabilitation, University of Iowa, Iowa City, IA, USA.
Department of Orthopedics and Rehabilitation, University of Iowa, Iowa City, IA, USA; Department of Biomedical Engineering, University of Iowa, Iowa City, IA, USA.
J Shoulder Elbow Surg. 2021 Nov;30(11):2629-2637. doi: 10.1016/j.jse.2021.04.039. Epub 2021 May 18.
Repair of the subscapularis following reverse shoulder arthroplasty (RSA) remains a controversial topic among surgeons. Poor rotator cuff muscle quality is associated with increased musculotendinous stiffness, and the subsequent effect of compromised tissue repair on RSA functional outcomes remains unclear. The objective was to investigate the influence of subscapularis stiffness together with glenoid component lateralization on pre- and postimpingement joint mechanics during external rotation after RSA.
A validated finite element model incorporating the Zimmer Trabecular Metal reverse system was used. The deltoid and subscapularis tendon were tensioned and wrapped around the joint prior to controlled shoulder external rotation. Baseline subscapularis stiffness, determined from cadaveric testing, was varied to 80%, 120% and 140% of baseline, to simulate a range of pliability associated with fatty infiltration and fibrosis. We evaluated the effects of varying subscapularis stiffness and the corresponding variation in joint tension with varying glenosphere lateralization (2, 4, and 10 mm) on the torque required to externally rotate the shoulder and the impingement/subluxation risk.
Prior to any impingement, the torques required to externally rotate the shoulder ranged from 22-47 Nm across the range of parameters studied, with the greatest torques required for the 10-mm glenosphere lateralization. The impact of increasing subscapularis stiffness on torque requirements was most pronounced at the 10-mm lateralization, as well. A 20% increase in subscapularis stiffness necessitated a 7%-14% increase in preimpingement torque, whereas a 40% stiffness increase was associated with a 12%-27% increase in torque. Torque was proportional to lateralization. When lateralization was increased from 2 to 4 mm, the preimpingement torque increased by 10%-13%, whereas a 10-mm lateralization necessitated a 35%-62% torque increase relative to 2 mm of lateralization. Increased subscapularis stiffness did not limit impingement-free range of motion or substantially decrease postimpingement subluxation in this model.
Mechanical gains achieved through lateralization may be hindered by increased torque demands, especially when a stiffer subscapularis is repaired. As lateralization increases subscapularis tension, greater torque is required to externally rotate the shoulder. The torque required for external rotation has been reported between 15-50 Nm. Subscapularis repair with the simulated increases in stiffness requires relative increases in torque that the reconstructed shoulder may not be able to physically produce to rotate the glenohumeral joint, particularly at 10-mm lateralization. These results suggest that subscapularis repair may not be indicated in cases where a lateralized glenoid component is used and the subscapularis is compromised.
反向肩关节置换术(RSA)后修复肩胛下肌仍然是外科医生之间有争议的话题。较差的肩袖肌肉质量与增加的肌腱-肌肉僵硬有关,并且随后组织修复对 RSA 功能结果的影响仍不清楚。目的是研究肩胛下肌僵硬以及肩胛下肌与肩胛盂组件侧方化对 RSA 后外旋时撞击前和撞击后关节力学的影响。
使用经过验证的包含 Zimmer Trabecular Metal 反向系统的有限元模型。在控制肩部外旋之前,将三角肌和肩胛下肌腱拉紧并包裹在关节周围。从尸体测试中确定的肩胛下肌初始刚度变化为初始刚度的 80%、120%和 140%,以模拟与脂肪浸润和纤维化相关的各种柔韧性。我们评估了变化的肩胛下肌刚度以及与肩胛盂侧方化(2、4 和 10mm)相对应的关节张力变化对外部旋转肩部所需扭矩以及撞击/半脱位风险的影响。
在任何撞击之前,在所研究的参数范围内,外部旋转肩部所需的扭矩范围为 22-47Nm,其中 10mm 肩胛盂侧方化所需的扭矩最大。随着肩胛下肌刚度的增加,对扭矩要求的影响在 10mm 侧方化中最为明显。肩胛下肌刚度增加 20%,则撞击前扭矩需要增加 7%-14%,而刚度增加 40%则与扭矩增加 12%-27%相关。扭矩与侧方化成正比。当侧方化从 2mm 增加到 4mm 时,撞击前扭矩增加 10%-13%,而 10mm 的侧方化相对于 2mm 的侧方化需要 35%-62%的扭矩增加。在这个模型中,增加的肩胛下肌刚度并没有限制无撞击的运动范围,也没有显著减少撞击后的半脱位。
通过侧方化获得的机械增益可能会受到增加的扭矩需求的阻碍,尤其是在修复更硬的肩胛下肌时。随着肩胛下肌张力的增加,外部旋转肩部所需的扭矩更大。据报道,外部旋转所需的扭矩在 15-50Nm 之间。模拟增加的刚度修复肩胛下肌需要相对增加的扭矩,而重建的肩部可能无法实际产生以旋转盂肱关节,尤其是在 10mm 侧方化时。这些结果表明,在使用侧方化肩胛盂组件且肩胛下肌受损的情况下,可能不需要修复肩胛下肌。