Purpose of the study: A systematic isokinetic assessment of both shoulders was performed in 103 men with shoulder instability subsequent to several anterior or antero-inferior trauma-induced dislocations. The assessment was part of the preoperative workup which included a clinical examination and an imaging protocol (standard x-rays + tomographies as needed). The purpose of the present study was to evaluate the force of the rotator muscles of the injured shoulder and to compare the findings with those obtained for the healthy shoulder. The objective was to determine the impact of instability on muscle balance in the injured shoulder.

Material and methods: This study concerned 103 men, mean age 24.8 years. The injured shoulder was dominant for 65 and non-dominant for 38. Time from the first episode of instability and the test was at least 2 months. One operator performed all tests using a unique dynamometer: Cybex Norm operating in concentric mode at 60 to 180/s.

Results: Overall, the results for 103 subjects at 60/s did not reveal any difference between the injured and the healthy side for internal rotators. There was a 2% deficit for the external rotators. At 180/s, the deficit was 5% for the internal rotators and 3% for the external rotators. For the injured dominant shoulders (n=65 subjects): at 60/s, there was no deficit; at 180/s, the deficit was 2% for internal rotators and 1% for internal rotators. For the injured non-dominant shoulders (n=38 subjects: the deficit was less than 10% compared with the healthy side for both 60/s and 180/s.

Conclusion: No significant deficit in internal or external rotation power was observed in the injured shoulder. Inclusion of an isokinetic test as a systematic part of the preoperative work-up for post-trauma instability in male subjects would not be warranted. The present findings can be used as control data for research involving non-trauma-induced uni- or multidirectional shoulder instability.