Background

Conflicting theories exist about the underlying cause of chronic subacromial pain in the middle-aged population. We aim to improve our understanding of kinematics and muscle activation in subacromial pain syndrome to provide insight in its pathophysiology.

Methods

In a cross-sectional comparison of 40 patients with subacromial pain syndrome and 30 asymptomatic controls, three-dimensional shoulder kinematics and electromyography-based co-contraction in 10 shoulder muscles were independently recorded. Glenohumeral and scapulothoracic kinematics were evaluated during abduction and forward flexion. Co-contraction was expressed as an activation ratio, specifying the relative agonistic and antagonistic muscle activity in each muscle.

Findings

During abduction and forward flexion, the contribution of glenohumeral motion to elevation and glenohumeral external rotation was lower in subacromial pain syndrome (at 120⁰ abduction: −9°, 95% CI -14°- -3°; and − 8°, 95% CI -13°--3°, respectively), and was compensated by more scapulothoracic motion. The pectoralis major's activation ratio was significantly lower (Z-score: -2.657, P = 0.008) and teres major's activation ratio significantly higher (Z-score: -4.088, P < 0.001) in patients with subacromial pain syndrome compared to the control group.

Interpretation

Reduced glenohumeral elevation and external rotation in subacromial pain syndrome coincided with less teres major antagonistic activity during elevation. These biomechanical findings provide a scientific basis for intervention studies directed at stretching exercises to reduce glenohumeral stiffness in the treatment of subacromial pain syndrome, and teres major strengthening to improve humeral head depressor function.

中文翻译：

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肩峰下疼痛综合征患者和无症状对照者的运动学和肌肉激活

背景

关于中年人群慢性肩峰下疼痛的根本原因存在相互矛盾的理论。我们的目标是提高我们对肩峰下疼痛综合征运动学和肌肉激活的理解，以深入了解其病理生理学。

方法

在对 40 名肩峰下疼痛综合征患者和 30 名无症状对照者的横断面比较中，独立记录了 10 块肩部肌肉的 3D 肩部运动学和基于肌电图的协同收缩。在外展和前屈期间评估盂肱和肩胛胸运动学。共收缩表示为激活比率，指定每块肌肉中的相对激动和拮抗肌肉活动。

发现

在外展和前屈期间，肩峰下疼痛综合征中盂肱运动对抬高和盂肱外旋的贡献较低（外展 120 ⁰时：-9°，95% CI -14°- -3°；和 - 8°，95 % CI -13°--3°，分别），并通过更多的肩胛胸运动得到补偿。 与对照组相比，肩峰下痛综合征患者胸大肌激活率显着降低（Z -score：-2.657，P  =0.008），大圆肌激活率显着升高（Z-score：-4.088，P <0.001） .

解释

肩峰下疼痛综合征中盂肱关节抬高和外旋减少与抬高过程中大圆肌拮抗活动的减少相吻合。这些生物力学研究结果为干预研究提供了科学基础，这些研究旨在通过伸展运动来减少肩峰下疼痛综合征治疗中的盂肱关节僵硬，并通过大圆肌强化来改善肱骨头抑制功能。