Biceps tenodesis with interference screw fixation: a biomechanical comparison of screw length and diameter.

PURPOSE To evaluate the effect of screw length and diameter on the mechanical properties of biceps tenodesis (BT) with an interference screw in 2 different locations (proximal and distal). METHODS We randomized 42 fresh-frozen human cadaveric shoulders (mean age, 65 ± 8 years) into 6 groups (n = 7): arthroscopic proximal BT using 7 × 15-, 7 × 25-, 8 × 15-, or 8 × 25-mm interference screws or distal subpectoral BT with 7 × 15- or 8 × 15-mm interference screws. Each repaired specimen was mounted onto a materials testing machine, preloaded to 5 N for 2 minutes, cycled from 5 to 70 N for 500 cycles (1 Hz), and loaded to failure (1 mm/s). Displacement during cyclical loading, pullout stiffness, and ultimate load to failure were computed, and the mechanism of failure was noted. RESULTS All failures occurred at the tendon-screw interface. There was no statistically significant difference in ultimate displacement among all groups in the ultimate load to failure, displacement at peak load, and stiffness. CONCLUSIONS There is no difference in ultimate load to failure, displacement at peak load, and stiffness of BT with regard to screw length or diameter at both proximal and distal tenodesis locations. These data would support use of a smaller-diameter and shorter implant for BT both proximally and distally. CLINICAL RELEVANCE The results may serve as a guide to the orthopaedic surgeon performing proximal BT in selecting the appropriate interference screw. When possible, we recommend using the smallest screw size available to minimize risk of stress fracture at the tenodesis site.