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.