RESUMO
Posterosuperior (or internal) impingement at the shoulder is defined as contact between the underside of the supraspinatus or infraspinatus tendons with the posterosuperior labrum during extreme external rotation and abduction. In many cases, this contact damages the tendon and causes mirror posterosuperior labrum deterioration. The primary aim of this study was to define whether this contact occurs normally in patients who do not have a rotator cuff tear. METHODS: We evaluated 100 shoulders in 100 patients. All patients were operated on in the beach chair position. After introducing the scope through the posterior portal, contact between the articular side of the rotator cuff and the posterosuperior labrum was noted as being present or absent when the arm was cocked in 90° abduction and 90° external rotation (90/90) then the arm was cocked in 140° abduction and maximum external rotation (140/Max). RESULTS: Contact was observed in 69% of patients in the 90/90 cocked position and in 94% of patients in the 140/Max cocked position. We found a correlation between the presence of rotator cuff and/or labrum lesions and the patient regularly performing arm-cock movements (p=0.035). DISCUSSION: Contact between the underside of the supraspinatus tendon and the posterosuperior labrum occurs physiologically. Repetitive arm-cock movements may contribute to macroscopic lesions of the underside of the rotator cuff and posterosuperior labrum. LEVEL OF EVIDENCE: IV, basic science study.