Laboratory for Kinematics and Neuromechanics, Leiden University Medical Center, Leiden, The Netherlands.
J Biomech. 2010 Aug 10;43(11):2049-54. doi: 10.1016/j.jbiomech.2010.04.012. Epub 2010 May 10.
In patients with rotator cuff tears lost elevation moments are compensated for by increased deltoid activation. Concomitant proximal directed destabilizing forces at the glenohumeral joint are suggested to be compensated for by 'out-of-phase' adductor activation, preserving glenohumeral stability. Aim of this study was to demonstrate causality between moment compensating deltoid activation and stability compensating 'out-of-phase' adductor muscle activation. A differential arm loading with the same magnitude of forces applied at small and large moment arms relative to the glenohumeral joint was employed to excite deltoid activation, without externally affecting the force balance. Musculoskeletal modeling was applied to analyze the protocol in terms of muscle forces and glenohumeral (in)stability. The protocol was applied experimentally using electromyography (EMG) to assess muscle activation of healthy controls and cuff tear patients. Both modeling and experiments demonstrated increased deltoid activation with increased moment loading, which was higher in patients compared to controls. Model simulation of cuff tears demonstrated glenohumeral instability and related 'out-of-phase' adductor muscle activation which was also found experimentally in patients when compared to controls. Through differential moment loading, the assumed causal relation between increased deltoid activation and compensatory adductor muscle activation in cuff tear patients could be demonstrated. 'Out-of-phase' adductor activation in patients was attributed to glenohumeral instability. The moment loading protocol discerned patients with cuff tears from controls based on muscle activation.
在肩袖撕裂的患者中，由于三角肌的激活增加，失去的抬高力矩得到了补偿。同时，肱骨头关节处向近端的不稳定力被认为是通过“非同步”内收肌的激活来补偿的，从而保持了盂肱关节的稳定性。本研究的目的是证明力矩补偿三角肌激活与稳定性补偿“非同步”内收肌肌肉激活之间的因果关系。采用不同的手臂加载方式，在相对于盂肱关节的小力矩臂和大力矩臂上施加相同大小的力，以激发三角肌的激活，而不对外力平衡产生影响。肌骨建模被用于分析该方案在肌肉力量和盂肱（内）稳定性方面的效果。该方案通过肌电图（EMG）在健康对照组和肩袖撕裂患者中进行了实验评估，以评估肌肉的激活情况。建模和实验都表明，随着力矩加载的增加，三角肌的激活增加，而患者的三角肌激活比对照组更高。对肩袖撕裂的模型模拟表明盂肱关节不稳定，并与相关的“非同步”内收肌肌肉激活有关，与对照组相比，这在患者中也通过实验得到了证实。通过差动力矩加载，可以在肩袖撕裂患者中证明三角肌激活增加与内收肌代偿激活之间的假设因果关系。患者中的“非同步”内收肌激活归因于盂肱关节不稳定。基于肌肉激活，力矩加载方案可以将肩袖撕裂患者与对照组区分开来。
