The diagnostic value of the shoulder rotator cuff muscles’ isometric force testing

The most prevalent group of disorders of human shoulder is related to the muscles of the rotator cuff. In order to develop a mechanical method for rotator cuff muscles’ evaluation, we hypothesized that measurement of the isometric force generated by the individual muscle of the rotator cuff might detect the variations, which are characteristic to the different disorders of rotator cuff muscles in adults. The isometric force of supraspinatus, infraspinatus and subscapularis muscles were measured in patients with rotator cuff tears, calcific tendinitis and subacromial impingement syndrome, 30 patients with each disorder, and compared to the normal values from our previous study. Torque of the force was calculated and normalized to lean body mass. The profiles of the mean torque-time curves of each group were compared statistically. We found the expected significantly lower profiles of the torque-time curves of all the tested rotator cuff muscles in comparison to the normal values. The best resolution between the curves of different study groups was found in the testing of the infraspinatus muscles. Therefore the previously unrecognized variations of rotator cuff muscles’ isometric strength build up patterns in the common disorders involving the rotator cuff muscles were revealed. The presented data might be a basis for the future development of a simple mechanical diagnostic method for identification of the abnormal patterns of muscle isometric strength in patients with rotator cuff muscles’ pathology.