Steenbrink F, de Groot J H, Veeger H E J, Meskers C G M, van de Sande M A J, Rozing P M
Department of Orthopaedics, Leiden University Medical Centre, The Netherlands.
Man Ther. 2006 Aug;11(3):231-7. doi: 10.1016/j.math.2006.07.004.
A mechanical deficit due to a massive rotator cuff tear is generally concurrent to a pain-induced decrease of maximum arm elevation and peak elevation torque. The purpose of this study was to measure shoulder muscle coordination in patients with massive cuff tears, including the effect of subacromial pain suppression. Ten patients, with MRI-proven cuff tears, performed an isometric force task in which they were asked to exert a force in 24 equidistant intervals in a plane perpendicular to the humerus. By means of bi-polar surface electromyography (EMG) the direction of the maximal muscle activation or principal action of six muscles, as well as the external force, were identified prior to, and after subacromial pain suppression. Subacromial lidocaine injection led to a significant reduction of pain and a significant increase in exerted arm force. Prior to the pain suppression, we observed an activation pattern of the arm adductors (pectoralis major pars clavicularis and/or latissimus dorsi and/or teres major) during abduction force delivery in eight patients. In these eight patients, adductor activation was different from the normal adductor activation pattern. Five out of these eight restored this aberrant activity (partly) in one or more adductor muscles after subacromial lidocaine injection. Absence of glenoid directed forces of the supraspinate muscle and compensation for the lost supraspinate abduction torque by the deltoideus leads to destabilizating forces in the glenohumeral joint, with subsequent upward translation of the humeral head and pain. In order to reduce the superior translation force, arm adductors will be co-activated at the cost of arm force and abduction torque. Pain seems to be the key factor in this (avoidance) mechanism, explaining the observed limitations in arm force and limitations in maximum arm elevation in patients suffering subacromial pathologies. Masking this pain may further deteriorate the subacromial tissues as a result of proximal migration of the humeral head and subsequent impingement of subacromial tissues.
由于巨大的肩袖撕裂导致的机械功能障碍通常与疼痛引起的最大手臂抬高和峰值抬高扭矩降低同时存在。本研究的目的是测量巨大肩袖撕裂患者的肩部肌肉协调性，包括肩峰下疼痛抑制的影响。10名经MRI证实存在肩袖撕裂的患者进行了等长力量任务，要求他们在垂直于肱骨的平面内的24个等距间隔处施加力。通过双极表面肌电图（EMG），在肩峰下疼痛抑制前后，确定了六块肌肉的最大肌肉激活方向或主要作用方向以及外力。肩峰下利多卡因注射导致疼痛显著减轻，施加的手臂力量显著增加。在疼痛抑制之前，我们观察到8名患者在进行外展力传递时，手臂内收肌（胸大肌锁骨部和/或背阔肌和/或大圆肌）的激活模式。在这8名患者中，内收肌激活与正常内收肌激活模式不同。这8名患者中有5名在肩峰下利多卡因注射后，一块或多块内收肌（部分）恢复了这种异常活动。冈上肌缺乏指向关节盂的力，三角肌代偿失去的冈上肌外展扭矩，导致盂肱关节内的不稳定力，随后肱骨头向上移位并引起疼痛。为了减少向上的平移力，手臂内收肌将协同激活，但会以牺牲手臂力量和外展扭矩为代价。疼痛似乎是这种（避免）机制的关键因素，解释了肩峰下病变患者中观察到的手臂力量限制和最大手臂抬高限制。掩盖这种疼痛可能会由于肱骨头近端移位和随后肩峰下组织的撞击而进一步恶化肩峰下组织。
