Department of Biomedical Engineering and Chemical Engineering, The University of Texas at San Antonio, San Antonio, TX, USA.
Biomechanics Core, Mayo Clinic, Rochester, MN, USA.
J Biomech. 2022 Nov;144:111340. doi: 10.1016/j.jbiomech.2022.111340. Epub 2022 Oct 5.
Rotator cuff (RC) muscles act as force couples to stabilize the glenohumeral joint and enable shoulder motion. We investigated the moment arms of anatomical subregions of the supraspinatus (SSP), infraspinatus (ISP), subscapularis (SSC), and the teres minor muscles during flexion. Eight fresh-frozen cadaveric shoulders were obtained and the anatomical subregions of the RC muscles were identified. Sutures were secured for each subregion at the musculotendinous junction and excursion during flexion from 30° to 90° at 10° increments was measured using a 3-D digitizing system. Kruskal-Wallis test followed by the Bonferroni post-hoc test was used to assess differences from subregions within a single muscle. There were significant differences in moment arms between the subregions from each RC muscle (P < 0.001). The anterior-superficial and -middle subregions of the SSP muscle presented positive (flexor) and decreasing moment arms with increasing flexion. The posterior-deep subregion showed moment arms with positive but decreasing values up to 65°, and negative (extensor) moment arms at larger angles. Subregions from the ISP showed positive and almost constant moment arms throughout range of motion, while the teres minor presented negative and almost unaltered moment arms. The superior and middle subregions of the SSC showed positive, but decreasing, moment arms with increasing angles up to 75° flexion, with negative moment arms towards end-range. The inferior subregion presented negative moment arms throughout flexion. Our results indicated that the posterior deep subregion of SSP muscle seems to act as a flexor at early range and as a stabilizer at mid-to-end range of flexion.
肩袖（RC）肌肉作为力偶，稳定盂肱关节并实现肩部运动。我们研究了肩袖中冈上肌（SSP）、冈下肌（ISP）、肩胛下肌（SSC）和小圆肌（TM）的解剖亚区在屈曲过程中的力臂。获得了 8 个新鲜冷冻的尸体肩部，并确定了 RC 肌肉的解剖亚区。在肌肌腱交界处为每个亚区固定缝线，并使用三维数字化系统测量从 30°到 90°以 10°增量屈曲时的运动范围。Kruskal-Wallis 检验后进行 Bonferroni 事后检验，以评估单个肌肉内亚区之间的差异。来自每个 RC 肌肉的亚区之间的力臂有显著差异（P < 0.001）。SSP 肌肉的前浅层和中间亚区呈现出正（屈肌）和随着屈曲增加而减小的力臂。后深部亚区显示出正但逐渐减小的力臂，直至 65°，在更大角度时显示出负（伸肌）力臂。ISP 的亚区在整个运动范围内显示出正且几乎恒定的力臂，而小圆肌则表现出负且几乎不变的力臂。SSC 的上中和中亚区在 75°屈曲范围内呈正（但逐渐减小）力臂，在接近末端范围时呈现负力臂。下亚区在整个屈曲过程中呈现负力臂。我们的结果表明，SSP 肌肉的后深部亚区似乎在早期范围内作为屈肌，在中到末端范围内作为稳定器。
