Background Although rotator cuff contractions play an important role in stabilizing the glenohumeral joint, little is known about the role of these muscles in physiopathological recurrent anterior instability.
Objective To analyze the association between isokinetic internal rotator (IR) and external rotator (ER) muscle strength and glenohumeral joint instability in patients with nonoperated recurrent anterior instability.
Design Case-control study.
Setting Department of Physical Medicine and Rehabilitation, Laboratory setting.
Participants 48 subjects participated: 37 patients (25±8 yr, 179±6 cm, 74±9 kg) and 11 healthy nonathletic subjects (24±1 yr, 178±5 cm, 70±9 kg).
Interventions ER and IR strength of 37 patients with unilateral recurrent anterior post-traumatic shoulder dislocation were compared with those of 11 healthy nonathletic subjects. Isokinetic shoulder IR and ER strength was evaluated with a Con-Trex dynamometer, in the seated position with 45° of shoulder abduction in the scapular plane. Tests were performed at 180°/s, 120°/s and 60°/s in concentric mode for both sides.
Main outcome measurements Peak torque normalised to body weight for IR and ER and ER/IR ratio were calculated for each angular velocity. The association between IR and ER strength and shoulder instability was analyzed by side-to-side comparisons and comparisons to the control group.
Results The association between shoulder instability and IR and ER strength was associated with side-to-side differences (p<0.05). By comparisons to a control group, strength values were lower on the pathological shoulder side than on the healthy homolateral shoulder side of controls at 180°/s and 120°/s (p<0.05). The side-to-side differences were increased when the nondominant side was involved and were decreased when dominant side was involved. We found no association between glenohumeral joint instability and ER/IR ratio.
Conclusion IR and ER strength weakness was associated with recurrent anterior instability and side-to-side differences depended on the dominance of the side involved.
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