The biomechanical study of peri-scapular muscle based on electromyography

Abstract

Biomechanical study of peri-scapular muscle based on electromyography Backgound: Scapular dyskinesis, which is defined as the motion and positional abnormality of scapula, is found in association with rotator cuff disease and various kinds of shoulder pathology. In terms of rotator cuff tear, it is not clear the rotator cuff tear is caused by dyskinesis or rotator cuff tear effect on dyskinesis. Most of researches which examined periscapular muscles based on surface electromyography(EMG) targeting impingement patients versus normal. In this study, we estimated activation and deactivation timing of periscapular muscles using surface EMG in rotator cuff tear and repaired patients. Hypothesis: We hypothesized that the dyskinesis of scapula would be more apparent in rotator cuff tear than impingement patients and we could find out the relationship between rotator cuff tear and dyskinesis by comparing rotator cuff tear and repaired patients. Study design: Cross sectional study, single center Methods: We attached surface EMG to the periscapular muscles which consist of upper trapezius(UT), lower trapezius(LT), serratus anterior(SA), middle deltoid(MD). Based on the electromyography, we acquired the activation latency time and deactivation time of peri-scapular muscles, not muscle activation ratio (%). We assumed muscle activation ratio (%), which require maximum volumetric contraction of each muscle, could be easily interfered by shoulder pain of rotator cuff tear. Data analysis were performed by the Matlab and used Delsys Trigo surface electromyography. We recruited 21 subjects including subjects with normal shoulder(7), full-thickness rotator cuff tear patients(7), rotator cuff repaired patients without re-tear of stiffness(7). The territory of rotator cuff tear were confirmed by preoperative MRI and the re-tear complication was assessed by 6 month follow-up MRI after surgery. Subjects were asked to do ten times of shoulder elevation in scapular plane at the speed of 2 sec/cycle and 6 sec/cycle. During the experiment, the examiner provided subjects with voice and visual cue for action. Results: The result showed that, in normal shoulder group, the peri-scapular muscle activated in the order of UT, SA and LT. However, in the group of rotator cuff tear, serratus anterior showed particularly late activation time in terms of activation latency. At the speed of 2 sec/cycle, activation time of serratus anterior delayed more. Deactivation time of SA in rotator cuff tear group were earlier than repaired and normal group. Interestingly, all of the result of activation and deactivation timing of SA showed a tendency to return to normal in rotator cuff repaired group. Conclusion: It is not enough to say that abnormal scapular movement is caused by rotator cuff tear. Our result showed that repaired rotator cuff and rehabilitation helped to return back to normal scapular movement in terms of activation pattern of periscapular muscle. Small number of subjects and mixed treatment of surgery and rehabilitation is a limitation of our research. Further investigation are needed to find statistically meaningful activation pattern of parascapular muscles in patients with rotator cuff tear and repair.

Key words : Scapular dyskinesis, rotator cuff tear, surface electromyography, scapular stabilizer, serratus anterior