Internal impingement of the shoulder: a clinical and arthroscopic analysis.

McFarland EG, Hsu CY, Neira C, O’Neil O. J Shoulder Elbow Surg 1999 Sep-Oct;8(5):458-60.

Internal impingement was first described by Walch in 1992 and defined as contact between the supraspinatus tendon and posterior-superior glenoid rim with the shoulder in the cocked, throwing position of 90 degrees of abduction and maximum external rotation. The hypothesis of the study was that this contact may be seen in patients who are not throwing athletes nor in those who have instability. One hundred five consecutive patients who underwent shoulder arthroscopy were prospectively studied with preoperative history and physical examination. All patients underwent general anesthesia and arthroscopy with a standard posterior portal. With the patient under arthroscopy the arm was placed in abduction and external rotation until contact was made or until full elevation was reached. Eighty-five percent (N = 90) of the patients made contact between the rotator cuff and glenoid rim at an average of 95 degrees of abduction and 74 degrees of external rotation. No statistically significant relationship was seen (P > .05) between the position of contact at internal impingement and mechanism of injury, throwing versus nonthrowing, instability, rotator cuff tear, preoperative external rotation, or preoperative impingement signs. The intraoperative finding of contact of the rotator cuff to the posterosuperior glenoid with the arm in abduction and external rotation can occur in a wide spectrum of shoulder disease and is not limited to the throwing athlete. Not all patients with increased laxity and instability demonstrate this contact, suggesting that these factors may not be essential for internal impingement.