Abstract
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.
Highlights
Disorders of shoulder which are related to the pathological processes in the muscles of rotator cuff are very common [1,2,3,4]
Supraspinatus Muscle Testing In the testing of SS muscle we found a significantly lower profiles of the torque time curves in all three pathological conditions in comparison to the normal values, i.e. average maximal torque in patients with subacromial impingement, calcific tendinitis and SS tears were 25.9 +/− 8.3, 22.6 +/− 5.6 and 22.9 +/− 5.5 N*m/kg respectively, vs. normal values of 61.8 +/− 18.3 N*m/kg, p < 0.001, (Figure 3)
In the testing of IS muscle we found a significantly lower profiles of the torque, time curves in all three pathological conditions in comparison to the normal values, i.e. average maximal torque in patients with subacromial impingement, calcific tendinitis and SS tears were 20.3 +/− 6.2, 5.7 +/− 2.9 and 26.3 +/− 6.5 N*m/kg respectively, vs. normal values of 40.4 +/− 10.4 N*m/kg, p < 0.001, (Figure 4)
Summary
Disorders of shoulder which are related to the pathological processes in the muscles of rotator cuff are very common [1,2,3,4]. The diagnosis of rotator cuff muscles’ pathology is usually based on an initial physical examination, which has a limited prediction values, and can be established with a high precision by much more sophisticated imaging modalities, like ultrasound and MRI scans. Till recently comprehensive data on the isometric force generation by the rotator cuff muscles in normal population, including variations according to gender, age and dominancy, were unavailable and the evaluation of rotator cuff pathology by measurement of the generated force was impossible because of the lack of reference for a comparison. In that study, based on evaluation of shoulders of 400 normal volunteers, we recorded the variations of the profiles of torque-time curves of isometric force which are generated by supraspinatus (SS), infraspinatus (IS) and subscapularis (SSC) muscles according to the limb dominancy, age and gender. In the current study we used these data as a reference in order to evaluate patients with rotator cuff pathology by mechanical
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