Introduction
As shoulder arthroscopy progressed, surgeons noticed an association between partial articular-sided rotator cuff tears and superior labral lesions [1,2]. It has been proposed that this pathology is caused by contact between the posterior-superior margin of the glenoid and the humeral head when the arm is abducted and externally rotated [3,1]. This phenomenon has been labeled “Internal Impingement” as it is believed to result in impingement of the posterior-superior labrum and the articular side of the supraspinatus tendon [1]. Internal impingement is classically associated with throwing and other repetitive overhead athletic activities, particularly in the late cocking and early acceleration phases [4]. Over time, repetitive loading at the limits of the functional arc of motion leads to predictable osseous and soft-tissue adaptations which have been associated with internal impingement. Several pathological conditions may result including articular-sided rotator cuff tears, labral tears, biceps tendonitis, and anterior shoulder instability [5].
Over time, additional theories have emerged to explain the common association between articular-sided rotator cuff tears and superior labral lesions. Burkhart et al proposed that these lesions develop over time due to the excessive shear and torsional forces placed on the shoulder by repetitive abduction and external rotation [4]. Andrews et al proposed that repetitive eccentric loading leads to similar pathology [6]. Although the true etiology of these lesions remains the subject of debate, the concept of internal impingement remains an important framework for understanding the painful shoulder in an overhead athlete.
The prevalence of internal impingement has not been well established due to the constellation of findings that characterize this condition and its strong association with other pathological lesions of the shoulder [5]. However, several authors have identified internal impingement as a leading cause of partial articular-sided rotator cuff tears in throwing athletes [5,7]. The purpose of this case report is to describe a novel etiology of internal impingement between the biceps tendon and the undersurface of the supraspinatus tendon leading to a symptomatic articular-sided rotator cuff tear. The patient’s symptoms persisted despite initial treatment with arthroscopic debridement and subacromial decompression. However, subsequent treatment with arthroscopic debridement and open sub-pectoral biceps tenodesis was successful and the patient has remained asymptomatic at latest follow-up. To the authors’ knowledge, no previous study has identified the biceps tendon as a cause of internal impingement.