Differences in the ultimate strength of the biceps anchor and the generation of type II superior labral anterior posterior lesions in a cadaveric model

Background: The pathogenesis of superior labral anterior posterior lesions remains controversial.

Hypothesis: The biceps anchor is more vulnerable to loading with a posterior vector as opposed to an in-line pull.

Study design: Controlled laboratory study.

Methods: Eight pairs of cadaveric shoulders were dissected, and the biceps tendon was loaded to failure in 1 of 2 loading patterns. Loading pattern A was meant to simulate the eccentric load of the biceps in the deceleration phase of throwing; loading pattern B was meant to simulate the posterior biceps load of the late cocking phase.

Results: The biceps anchor demonstrated significantly increased ultimate strength with in-line loading (group A, 508 N) as opposed to posterior loading (group B, 262 N, P < .001). All group B specimens failed at the biceps anchor, resulting in a type II superior labral anterior posterior lesion. Specimens in group A did not create a superior labral anterior posterior lesion.

Conclusions: Direction of biceps loading resulted in significant differences in the ultimate strength of the biceps anchor and the generation of superior labral anterior posterior lesions. The biceps anchor was significantly weaker when loaded with a posterior vector.

Relevance: The superior labrum may be most vulnerable to injury in late cocking. The reproducible generation of type II superior labral anterior posterior lesions may have applications as a biomechanical model.