The purpose of this study was to evaluate the role of the tension on the long head of the biceps tendon in the propagation of SLAP tears by studying the mechanical behavior of the torn superior glenoid labrum. A previously validated finite element model was extended to include a glenoid labrum with type II SLAP tears of three different sizes. The strain distribution within the torn labral tissue with loading applied to the biceps tendon was investigated and compared to the inact and unloaded conditions. The anterior and posterior edges of each SLAP tear experienced the highest strain in the labrum. Labral strain increased with increasing biceps tension. This effect was stronger in the labrum when the size of the tear exceeded the width of the biceps anchor on the superior labrum. Thus, this study indicates that biceps tension influences the propagation of a SLAP tear more than it does the initiation of a tear. Additionally, it also suggests that the tear size greater than the biceps anchor site as a criterion in determining optimal treatment of a type II SLAP tear. Keywords: FE; labrum; SLAP; biceps; propagation A tear of the superior labrum anterior posterior (SLAP tear) is a traumatic lesion in the superior glenoid labrum, which may include the attachment of the long head of the biceps tendon. This tear can contribute to significant pain and disability in the shoulder.1 SLAP tears are classified according to four or more subtypes.1,2 Among them, the type II tear involving detachment of both the superior labrum and the biceps tendon from the glenoid has been reported as the most common lesion.
1,2Both the motion of the humeral head and the traction on the biceps tendon have historically been implicated as predominant factors contributing to SLAP tears in numerous biomechanical studies of the tear mechanism. When SLAP tears were first described, it was hypothesized that they resulted from the traction imposed on the biceps tendon during repeated throwing movements.3 Later, several causal mechanisms were suggested for the SLAP tear, including the combination of humeral head compression and biceps tension 4 and the pulled and twisted biceps tendon.
5However, there is still a knowledge gap concerning how biceps tension relates to SLAP tear pathology and thus the optimal treatment of the SLAP tear. By testing labral strain at a specific phase during certain motions, specific activities at high risk for initiating a SLAP tear have been identified. [6][7][8][9] However, those studies neither observed the strain inside the labral tissue nor investigated the behavior of the labrum with an existing SLAP tear. Moreover, Costa et al. 10 reported that simple traction of the biceps tendon did not play a role in the initiation of the SLAP tear. The lack of clear understanding concerning the role of biceps tension in both the initiation and propagation of a SLAP tear leads to debates among surgeons on the proper treatment for the biceps tendon, which may include arthroscopic repair, debridement, tenodesis, tenotomy, ...