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Abstract & Commentary
Synopsis: Type II SLAP lesions result in additional laxity in the same quadrant of the shoulder, and subsequent internal impingement, stretch, and eventual tear of the rotator cuff.
Source: Morgan CD, et al. Type II SLAP lesions: Three subtypes and their relationships to superior instability and rotator cuff tears. Arthroscopy 1998;14:553-565.
Avulsions of the long head of the biceps tendon and labrum from the glenoid rim are termed superior labral anterior-to-posterior (SLAP) lesions. Of the four varieties, Type II lesions are the most symptomatic as they involve detachment of the biceps anchor with the labrum. The mechanism of injury is presumed to involve traction on the arm, such as deceleration during the follow-through while throwing. Morgan and associates arthroscopically subdivided 102 Type II SLAP lesions and noted that the mechanism of injury was specific to the location of detachment. Anterior lesions correlated with traumatic events, such as traction against a contracted biceps muscle. Posterior detachment, either isolated or combined with further detachment anteriorly, was three times more likely to be associated with repetitive throwing. Throwers noted increased pain in the cocking phase rather than in the follow-through, bringing into question the mechanism of injury. The Jobe relocation test with posterior pain in abduction and external rotation (which is relieved by posterior directed pressure on the humeral head) was found to be diagnostic of posterior or combined lesions. Arthroscopically, Morgan et al were able to visualize a "peel back" mechanism of torsion on the posterior labrum and biceps attachment when the shoulder is in this position. Thirty-one percent (32 patients) of patients also had rotator cuff tears, including 12 complete and 20 partial tears. All of the partial tears involved the undersurface of the rotator cuff and were lesion specific in location. That is, the posterior SLAP lesions were associated with posterior rotator cuff tears. Morgan et al conclude that Type II SLAP lesions result in additional laxity in the same quadrant of the shoulder, and subsequent internal impingement, stretch, and eventual tear of the rotator cuff.
Comment by David R. Diduch, MS, MD
Morgan et al help us to better understand the mechanism for SLAP lesions and make an excellent case for subdividing Type II lesions according to location. They demonstrate, with a large series, that anterior SLAP lesions are more frequently associated with a traumatic event, while posterior or combined SLAP lesions are three times more common in throwers. They arthroscopically explained this difference by identifying torsional force on the posterior labrum and biceps anchor (the "peel back" mechanism) when the arm is in a cocked position.
These posterior or combined lesions lead to secondary posterior superior instability, demonstrated by the "drive through" sign arthroscopically. Upon repair of the SLAP lesion, this "drive through" sign was corrected. Although posterior superior instability cannot result in dislocations because of the acromial roof, repetitive subluxation could damage the undersurface of the rotator cuff due to increased tensile forces and internal impingement. Thus, posterior SLAP lesions become associated with posterior rotator cuff tears. It is important for the arthroscopist to make this association at the time of surgery, so that both problems are corrected.
This study helps us to better understand the mechanism of injury for SLAP lesions and offers important treatment correlations. Throwers with pain during the cocking phase may develop a posterior Type II SLAP tear due to "peel back" forces. This results in posterior-superior laxity and possibly posterior rotator cuff tears. In addition to rotator cuff repair, the posterior SLAP lesion needs to be stabilized to prevent recurrence.