External to internal glenohumeral strength ratio in non-traumatic rotator cuff pathologies

Abstract

Background and study aims: A correct agonist -antagonist strength relationship for shoulder external and internal rotation is necessary for functional stability of the shoulder. This strength relationship is described by the ratio of external to internal strength (ER/IR).The aim of this stydy is to produce comparative data as regards the ER/IR ratio in subjects with different non-traumatic rotator cuff diseases. Design and setting: A cross-sectional study in an outpatient clinic in a tertiary care university hospital. Methods: In 55 subjects with rotator cuff disease (confirmed by physical examination and assessed by ultrasound and magnetic resonance arthrography), the ER/IR ratio of the shoulder was isometrically measured with a hand-held dynamometer and compared with values pertaining to the unaffected shoulder of the same individuals. Results: The mean ER/IR values in the overall group were 0.89 (SD 0.18) and 0.94 (SD 0.22) for the affected and unaffected shoulders, respectively. The ratio was 0.87 (SD 0.23) in patients with subdeltoid bursitis, 0.88 (SD 0.16) in rotator cuff tendinopathy and 0.87 (SD 0.22) in patients with rotator cuff tears. Conclusions: The ER/IR ratio appears to be similar between the affected and unaffected shoulders of subjects with nontraumatic cuff pathologies.