Biomechanical properties of suprapectoral biceps tenodesis: double knotless screw fixation is superior to single knotless screw fixation

Introduction: The purpose of this study is to biomechanically evaluate a new technique of double knotless screw fixation for suprapectoral biceps tenodesis and compare the results with that of the single knotless screw fixation as well as the interference screw fixation. Methods: 24 fresh-frozen human cadaveric shoulders with a mean age of 68.3 ± 9 years were studied. The specimens were randomly divided into three experimental biceps tenodesis groups (n = 8): single knotless screw, double knotless screw and interference screw. Each tenodesis specimen was mounted on a mechanical testing machine, preloaded for 2 min at 5 N, tested with cyclic loading from 5 to 70 N for 500 load cycles and subjected to an axial load to failure test (1 mm/s). The ultimate failure load, stiffness, cyclic displacement and mode of failure were evaluated. Results: The interference screw fixation had the highest ultimate failure load (215.8 ± 43.1 N) and stiffness (25.7 ± 5.2 N/mm) which were significantly higher than the corresponding results for the single and double knotless screw groups (P = 0.0029). The double knotless screw group had the second highest ultimate failure load (162.8 ± 13.8 N) and stiffness (15.1 ± 4.1 N/mm) which were significantly higher than the corresponding results for the single knotless screw technique (P = 0.0002). The most common mode of failure was suture slippage for both the double (7/8) and single knotless screw (6/8) groups while biceps tendon tearing occurred most often for the interference screw group (6/8). Conclusion: In this biomechanical study, the double knotless screw fixation was found to have a significantly greater ultimate failure load and stiffness than the single knotless screw fixation but lower values than the interference screw fixation.