Contribution to the study of the pathogenesis of type II superior labrum anterior-posterior lesions: a cadaveric model of a fall on the outstretched hand.

With a cadaveric model, we studied the effects on the superior labrum-biceps tendon complex of a fall on the outstretched hand to assess one of the supposed mechanisms of creation of superior labrum anterior-posterior (SLAP) lesions. Ten shoulders were used to simulate either a forward or a backward fall with a custom shoulder-testing apparatus capable of simulating muscle forces, attached to a servohydraulic testing machine (INSTRON 8500+). Impaction of the humeral head on the glenoid cavity was applied in 0.1 seconds. The presence or absence of a SLAP lesion was determined. For the 5 shoulders used to simulate a forward fall, 5 type II SLAP lesions were found; for the 5 shoulders used to simulate a backward fall, only 2 type II SLAP lesions were observed. The role of shearing forces seems to be a major factor in the pathogenesis of these lesions, in association with predisposing anatomic factors.