Internal impingement of the shoulder in flexion.

Contact of the rotator cuff to the superior glenoid with the arm in flexion has been described and postulated to be a source of rotator cuff disease. The goals of the current study were to document the existence of internal impingement in flexion arthroscopically and to determine its prevalence in patients with various diseases. Also, we attempted to determine the clinical significance of internal impingement in flexion by investigating the associations between internal impingement in flexion and the preoperative and intraoperative findings. A consecutive case series of 376 patients having arthroscopy of the shoulder were entered prospectively into this study. During arthroscopy, intraarticular lesions were evaluated and the presence of contact of the rotator cuff to the superior glenoid and the degree of flexion making the contact were noted. Statistical analysis was done with two dependent variables defined: the presence of internal impingement in flexion and the flexion degree making internal impingement in flexion. Of the 376 patients, 277 (74%) had internal impingement in flexion and 99 (26%) did not have internal impingement in flexion. There were no statistically significant differences in the prevalence of internal impingement in flexion according to the primary diagnoses. Statistical analysis revealed that the presence of internal impingement in flexion was associated with Type II superior labrum anterior posterior (SLAP) lesions and the presence of internal impingement of the rotator cuff to the superior glenoid in abduction and external rotation. There was a significant relationship between rotator cuff disease and decreasing angle of contact for internal impingement in flexion. This study showed that internal impingement in flexion is common in a cohort of patients having shoulder surgery, with an overall prevalence of 74%, and that internal impingement in flexion may contribute to the development of Type II SLAP lesions and rotator cuff disease.