Nicolozakes Constantine P, Schmulewitz Julia S, Ludvig Daniel, Baillargeon Emma M, Danziger Margaret S, Seitz Amee L, Perreault Eric J
Department of Biomedical Engineering, Northwestern University, Evanston, IL, USA.
Shirley Ryan AbilityLab, Chicago, IL, USA.
Ann Biomed Eng. 2025 Jun;53(6):1328-1343. doi: 10.1007/s10439-025-03683-5. Epub 2025 Mar 18.
Active stability is essential to preventing dislocations and the focus of rehabilitation following dislocations. This is thought to arise from shoulder muscles compressing the humeral head into the glenoid (called concavity compression). However, shoulder muscles may also resist humeral head translation through increases in intrinsic muscle stiffness, an unexplored mechanism. Our objective was to quantify shoulder muscles' contributions to changes in glenohumeral stiffness, or the resistance to humeral head translation. We hypothesized that primary shoulder movers (e.g., the pectoralis major or deltoid) would differ from rotator cuff muscles in how much they increase glenohumeral stiffness because they leverage their intrinsic stiffness in addition to concavity compression.
We measured glenohumeral stiffness across a range of isometric muscle activation levels in shoulder abduction and used electromyography to estimate the contributions of rotator cuff muscles and primary shoulder movers. We then created a musculoskeletal model to evaluate individual muscle contributions to glenohumeral stiffness through both concavity compression and intrinsic muscle stiffness.
We found that muscle activity in primary shoulder movers was a better predictor of active glenohumeral stiffness than in rotator cuff muscles (R = 0.81 vs 0.36, P < 0.001). Our musculoskeletal model demonstrated that concavity compression is the primary stabilizing mechanism for most shoulder muscles, yet the muscles that increase glenohumeral stiffness the most also do so considerably through their intrinsic muscle stiffness.
Our results emphasize the importance of primary shoulder movers as active stabilizers of the glenohumeral joint and highlight their potential importance in preventing shoulder dislocations.
主动稳定性对于预防脱位以及脱位后的康复重点至关重要。人们认为这源于肩部肌肉将肱骨头压入关节盂（称为凹面压缩）。然而，肩部肌肉也可能通过增加固有肌肉僵硬度来抵抗肱骨头平移，这是一个尚未探索的机制。我们的目标是量化肩部肌肉对盂肱关节僵硬度变化（即对肱骨头平移的阻力）的贡献。我们假设主要的肩部运动肌（如胸大肌或三角肌）在增加盂肱关节僵硬度的程度上会与肩袖肌群不同，因为它们除了凹面压缩外还利用其固有僵硬度。
我们在肩部外展的一系列等长肌肉激活水平下测量了盂肱关节僵硬度，并使用肌电图来估计肩袖肌群和主要肩部运动肌的贡献。然后我们创建了一个肌肉骨骼模型，以评估各个肌肉通过凹面压缩和固有肌肉僵硬度对盂肱关节僵硬度的贡献。
我们发现主要肩部运动肌的肌肉活动比肩袖肌群的肌肉活动能更好地预测主动盂肱关节僵硬度（R = 0.81对0.36，P < 0.001）。我们的肌肉骨骼模型表明，凹面压缩是大多数肩部肌肉的主要稳定机制，但增加盂肱关节僵硬度最多的肌肉也通过其固有肌肉僵硬度显著增加了僵硬度。
我们的结果强调了主要肩部运动肌作为盂肱关节主动稳定器的重要性，并突出了它们在预防肩关节脱位方面的潜在重要性。
