Abstract
We present the use of dynamic electromyographic analysis (DEMG) in the diagnosis of muscle patterning instability. DEMG’s were requested in 168 of 562 muscle patterning shoulders with suspected subclinical or clinically complex muscle patterning instability. An experienced neurophysiologist (blinded to the clinical findings and direction of instability) inserted dual-wire tungsten electrodes into pectoralis major, latissimus dorsi, infraspinatus and anterior deltoid. Muscle activity was recorded during rest, flexion, abduction, extension, and cross-body adduction. 5 investigations were abandoned. The timing and magnitude of muscle activity was noted and compared to the clinical diagnosis and direction of instability. DEMG identified a total of 204 abnormal muscle patterns in 163 shoulders. The examination was normal in 13 patients (8%). A single muscle was abnormal in 63 shoulders, 2 muscles in 55, 3 muscles in 9, and all 4 muscles in one shoulder. Over-activation of pectoralis major was identified in 58%, and latissimus dorsi in 70%, of shoulders with anterior instability. In posterior instability, latissimus dorsi was overactive in 76%, anterior deltoid in 14% and infraspinatus was under-active in 24%. Pectoralis major and Latissimus dorsi were both overactive in 38% of anterior, 29% of posterior and 38% of multidirectional instability. Abnormal muscle patterns were identified in 52 shoulders with subclinical muscle patterning. A further 98 shoulders had 134 clinically abnormal muscle patterns. These were confirmed by DEMG in 57 cases (sensitivity 43%), and DEMG’s were normal in 77 (specificity 43%). DEMG also identified 65 additional muscles as abnormal in the 98 clinically abnormal shoulders. DEMG performed by an experienced neurophysiologist provides additional information regarding abnormal muscle activation in selected complex or subtle cases of muscle patterning instability in which clinical examination has a low sensitivity and specificity.
The abstracts were prepared by Cormac Kelly. Correspondence should be addressed to The Secretary, British Elbow and Shoulder Society, Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE
