Interference screw and suture anchor fixation for lateral extra-articular tenodesis yield no significant differences in load to failure, while staple fixation lags behind: A Cadaveric Biomechanical Study.

Purpose: To evaluate the biomechanical properties and failure mechanisms of lateral extra-articular tenodesis (LET) performed using onlay staple, inlay interference screw, and onlay all-suture anchor fixation techniques.

Methods: Twenty-four non-matched pairs of human cadaveric knees were randomized to receive either a cortical staple (n=8), interference screw (n=8), or all-suture anchor (n=8). A modified Lemaire LET technique was performed for all knees using their respective fixation technique. Biomechanical testing was performed using a tensile-testing apparatus (MTS Systems). All knees were subjected to an axially directed pre-load cycle and subsequently assessed for cyclic and load-to-failure outcomes. Results were analyzed via analysis of variance (ANOVA), Kruskal-Wallis, and post-hoc Tukey´s tests.

Results: Three staple-fixated LETs failed during the cyclic loading and were excluded from analysis. Average elongation after cyclic loading was 2.89 millimeters (mm) (staple), 2.06 mm (screw), and 3.51 mm (anchor) (p = 0.134). Average maximum load to failure was 174.1 N (staple), 250.8 N (screw), and 199.2 N (anchor) with a significant between-group difference on ANOVA testing (p = 0.023). Post-hoc analysis revealed staple fixation had a significantly lower maximum load than interference screw fixation (p=0.026). Displacement at maximum load was significantly higher in the anchor group (22.2 mm) compared to the staple (11.3 mm) (p=0.05).

Conclusion: While staple fixation resulted in early failure (174 N), both interference screw and anchor fixations (250 N and 199 N, respectively) are viable options for LET, with suture anchors offering less rigidity under high loads when compared with either fixation strategy. However, no differences were observed in elongation during cyclic loading.

Clinical relevance: Emerging literature has revealed a 70% tunnel convergence rate when utilizing an interference screw for femoral fixation of a LET. The results of the present time-zero cadaveric study explores the role of surface-based fixation methods, given that it may mitigate convergence risk.