Summary

There are no significant differences in load to failure between screw and suture anchor for femoral fixation of an LET, while staple fixation exhibits high rates of early failure and inferior load to failure

Abstract

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) 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, both interference screw and anchor fixations are viable options for LET, with suture anchors offering less rigidity under high loads.

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 study yield the surface based all-suture anchor as a viable alternative for LET fixation while diminishing the risk of convergence.

Keywords: lateral extra-articular tenodesis; anterior cruciate ligament; biomechanics, inlay versus onlay ligament fixation