Biomechanical evaluation of the origin of the long head of the biceps tendon

Purpose: Lesions of the superior glenoid labrum extending anterior and post erior (SLAP) have recently been recognized as important sources of shoulder pain and dysfunction. Among the 4 described types of SLAP lesions, the typ e II SLAP involves detachment of the superior labrum from the bony glenoid and destabilization of the origin of the long head of the biceps tendon (LH BT). The purpose of this cadaveric biomechanical study was to evaluate the relative contribution regarding linear stiffness and displacement under loa d of the 2 origins of the LHBT: the superior,glenoid labrum and the supragl enoid tubercle (the biceps anchor). Type of Study: Cadaveric biomechanical study. Methods: Seven pairs of fresh-frozen cadaveric shoulders were dissec ted free of all soft tissue except for the glenoid labrum and LHBT. Tension from 0 to 55 N was applied to the LHBT while keeping the tendon perpendicu lar to the face of the glenoid. Each specimen was tested for linear stiffne ss and biceps tendon displacement in the intact state, after releasing 1 of the LHBT origins, and after releasing the remaining origin. Results: The a verage stiffness of the LHBT origin was 103 N/mm. Sectioning the anchor alo ne resulted in a 52% reduction in linear stiffness, whereas only detaching the superior glenoid labrum from the 10 o'clock to the 2 o'clock position r esulted in a 15% reduction in linear stiffness. Maximum displacement of the biceps tendon origin in the intact state at the 55 N load averaged 0.99 mm . With a minimum load applied, displacement changed less than mm unless bot h origins were released. Conclusions: The results indicate that the biceps anchor is the primary restraint of the LHBT and that the superior labrum is a secondary restraint in regard to linear stiffness. However, disruption o f both restraints is required to produce the laxity typically seen in a typ e II SLAP lesion.