Proximal versus distal screw placement for biceps tenodesis: a biomechanical study.

ABSTRACT

PURPOSE: To assess the maximum and end torque of a fourth-generation composite humerus model with no screw inserted or with a screw inserted in the distal (subpectoral) position or proximal (suprapectoral) position. METHODS: 24 large-size, fourth-generation composite humeri were randomised to the control (n=8), proximal (n=8), or distal (n=8) group. For the latter 2 groups, an 8-mm-head interference screw (7x25 mm) was inserted at 1 cm proximal and 1 cm distal to the superior aspect of the insertion of the pectoralis major tendon, respectively. The maximum and end torque of each humerus was assessed. RESULTS: Respectively for the control, proximal, and distal groups, the maximum torque was 81.8, 78.7, and 74.3 Nm, and the end torque was 80.7, 78.6, and 71.8 Nm; only the difference between control and distal groups was significant (p=0.005 for maximum torque and p=0.033 for end torque). All fractures in both control and proximal groups involved the distal 1/3 humerus. In the distal group, the fractures involved either the distal 1/3 humerus (n=6) or the screw-hole (n=2); the difference between the 2 types of fracture was not significant in terms of maximum torque (75.7 vs. 70.0, p=0.086) or end torque (75.3 vs. 61.4, p=0.40). CONCLUSION: Compared with proximal placement of an interference screw, distal placement decreased the maximum torque (though not significantly) and may increase the risk of proximal humeral fracture.