Discussion
Previous biomechanical and clinical studies have demonstrated the concept of internal impingement [1-4]. In abduction and external rotation, the humeral head often contacts the superior glenoid, resulting in impingement of the articular side of the supraspinatus tendon and the superior labrum [1]. This impingement, in turn, can potentially lead to pathologic lesions of the rotator cuff and labrum [1,2]. Although alternative explanations for this pathology exist [4,6], this theory has served as a useful conceptual framework for understanding pathology commonly found in the overhead athlete. The purpose of this case report is to describe an alternative etiology of internal impingement involving impingement of the biceps tendon on the undersurface of the supraspinatus tendon.
The association between partial articular-sided rotator cuff tears and superior labral lesions is well documented in the literature [6,2,10,1]. It should be noted, however, that not all partial articular-sided rotator cuff tears are accompanied by superior labral lesions [11]. The fact that not all articular sided rotator cuff tears are accompanied by labral lesions leads us to believe that there are alternative causes of articular-sided rotator cuff tears other than internal impingement. Over time, additional theories have emerged to explain the common association between articular sided rotator cuff tears and superior labrum lesions. Burkhart et al proposed that these lesions can develop over time due to the excessive shear and torsional forces cause by repetitive abduction and external rotation [4]. Andrews et al proposed that repetitive eccentric loading can similarly lead to this pathology [6]. As demonstrated in this case report, we believe that direct impingement of the biceps tendon on the undersurface of the rotator cuff can lead to articular-sided rotator cuff tears.
Posterior biceps instability and friction may represent an under-diagnosed and under-recognized source of internal impingement. This may especially be true among patients whose symptoms persist despite adequate treatment of concomitant pathology. Partial articular-sided rotator cuff tears and type-1 labral lesions are typically treated non-operatively with good results [12]. When conservative treatment fails, arthroscopic debridement has been the standard of care [13]. However, some studies have reported suboptimal results with this treatment approach [14,10]. When partial tears of less than 50% thickness are treated with arthroscopic debridement, the incidence of progression to full-thickness tears ranges from 6.5-34.6% in the literature [13]. Our experience reflects these findings as we have observed high rates of persistent symptoms in our practice with debridement alone. This observation has led us to search for other potential pain generators in the shoulder that may be overlooked. The biceps tendon as a source of pain and pathology in the shoulder has been well described [15]. There are three primary sources of biceps-related shoulder pain: bicipital tendonitis, traction on a Type-2 SLAP tear, and biceps instability. Each of these conditions can be treated effectively with biceps tenodesis. In the case presented in this report, there was no evidence of significant bicipital tendonitis or labral detachment.
Multiple anatomic changes and pathologic conditions contribute to biceps instability in throwing athletes. Increased external rotation with repetitive throwing is achieved by shoulder adaptations including anterior capsule laxity and posterior capsule tightening [16,17]. Laxity of the superior glenohumeral and coracohumeral ligaments, which form the “biceps pulley” along with the supraspinatus and subscapularis, may contribute to biceps instability. Braun et al demonstrated that tears of both the anteromedial and posterolateral pulley are associated with biceps subluxation and dislocation from the bicipital groove [18]. Acute trauma can also cause biceps pulley lesions [19]. Swimmers such as our patient often have an element of underlying shoulder laxity [20,21]. Our patient’s history of competitive swimming and water polo may have contributed to posterior biceps instability and the resulting internal impingement seen intraoperatively (Figure 4B).
In addition, abduction and external rotation in the late cocking phase of throwing is known to shift the biceps tendon posteriorly [4]. In this position, the biceps tendon may assume a more vertical and posterior angle (as was observed in our patient during diagnostic arthroscopy in the 90-90 position). Burkhart et al attributed the “peel-back phenomenon” seen intraoperatively in patients with SLAP lesions to this posterior shift in biceps vector forces [22]. Of note, the patient presented in this case report had some evidence of labral fraying, but the biceps anchor was intact. Although the “peel-back phenomenon” was not observed, tension on the intra-articular biceps tendon in the late cocking phase may have resulted in posterior displacement and impingement on the rotator cuff without fully disrupting its anchor.
Several clinical studies have demonstrated an association between rotator cuff tears and biceps instability [8,23-26]. The LHB is stabilized by a sling formed by the supraspinatus and subscapularis tendons proximal to the bicipital groove [27]. Therefore, rotator cuff tears may increase and alter mechanical loading on the LHB and lead to progressive deterioration [24,23]. LHB lesions have been reported in 29-86% of patients with rotator cuff tears [26,24,23,8,25]. In a prospective study of 200 arthroscopic rotator cuff repairs, LHB subluxation or dislocation was observed in 45% of patients [23]. Posterior LHB instability was commonly observed with anterior supraspinatus tendon tears [16].
The are several weaknesses of this case report. First, this is an isolated case and it remains to be seen whether this approach is valid when applied to a larger patient population. Second, the patient underwent an additional debridement at the time of her second surgery, which may have contributed to the positive results. Third, biceps tenodesis is an effective treatment for biceps pathology. It is possible that the rotator cuff lesion was incidental and that the true pathology was intrinsic to the biceps tendon.
In summary, we present an interesting case report of a small, partial articular-sided supraspinatus tendon tear initially treated with arthroscopic debridement (Figure 1). Unfortunately, the patient did not improve with simple debridement. In addition, the tear was relatively small and was not felt to be large enough to be causing significant pain on its own. This led us to search for an alternative explanation for the patient’s shoulder pain. During arthroscopy, we observed direct impingement of the biceps tendon on the undersurface of the rotator cuff as the arm was abducted and externally rotated (Figure 4B). In addition, the remaining rotator cuff beyond this site of impingement was intact. This led us to perform an open biceps tenodesis. The patient recovered fully from this operation and is pain free at latest follow-up.