THE PREVALENCE OF INAPPROPRIATE MUSCLE SEQUENCING IN RECURRENT SHOULDER INSTABILITY

Abstract

Aim: To demonstrate that inappropriate sequencing of activation of shoulder muscles can cause shoulder instability.

Methods. The records of 933 cases of recurrent shoulder instability referred to a specialist shoulder service between 1993 and 2003 were reviewed. All patients were assessed clinically. Muscle patterning abnormality (Bayley 1986) was identified in 428 patients (46%). Confirmatory functional electromyography was performed in 166 (36%). Inappropriate pectoralis major activation was identified in 73% of anterior instability. In posterior instability, inappropriate activation of latissimus dorsi and anterior deltoid was present in 72% and infra-spinatus was suppressed in 19%. Arthroscopic assessment was performed in 141 (33%), identifying structural lesions of instability in 86 (20%).

All patients diagnosed with muscle patterning disorder received specilalist physical therapy using biofeedback. Symptomatic improvement or stability was achieved in 76% of patients with anterior instability but with no previous surgery, and in 53% of patients with previous surgery. Posterior instability was eliminated in 85% of cases.

Conclusion. Muscle patterning abnormalities contribute to recurrent instability of the shoulder in 46% of cases. The success of physical therapy in these patients is high.