Summary

Augmentation with a bioinductive, biocomposite absorbable structural scaffold imparts additional time zero biomechanical strength to ulnar collateral ligament repair alone, and restores valgus stability without over constraint.

Abstract

Background

Ulnar collateral ligament (UCL) repair with suture brace augmentation has been shown to have good time-zero biomechanical strength and short-term outcomes with more rapid return to play than traditional reconstruction techniques. However, there are concerns of intraarticular biocompatibility, and over-constraint or stress shielding with the use of nonabsorbable suture tape. Recently, an off-the-shelf bioinductive structural scaffold, that absorbs at 2 years and has more physiologic mechanical properties, has been FDA approved for augmentation of soft tissue repair. The purpose of this study is to assess the feasibility of the biomechanical performance of UCL repair augmented with this structural scaffold.

Materials And Methods

Seven cadaveric elbow specimens, from mid-forearm to mid-humerus were utilized. Sample size of 4 was determined, through power analysis using expected effect size from the literature, to yield a power of 0.8. The forearm was potted in neutral rotation. The surgical approach was performed, down to the level of the intact capsule and UCL (Figure 1A). The elbow then underwent valgus stress testing at 30, 60, and 90 degrees flexion, with a cyclical valgus rotational torque of 2-5 Nm, as described in prior studies of UCL repair, to establish the native state. Testing was then performed in 3 additional states (Figure 1B-D): UCL-transected, augmented UCL repair with scaffold, and repair alone with scaffold not fixed. The order of testing in relation to repair with scaffold, and repair alone without scaffold, was alternated for specimens to account for any possible elastic deformation through testing. The repair technique was based on the previously described Internal Brace-augmented repair, but with scaffold instead of suture tape (Figure 2). Valgus opening, measured in degrees, was compared among the 4 states, as repeated measures for statistical analysis.

Results

There was a significant difference between each of the 4 UCL repair states, at all flexion angles (P=0.001, <0.0001, and <0.0001 at 30, 60, and 90 degrees flexion, respectively by repeated measures ANOVA; Figure 3). Valgus opening was significantly improved with scaffold-augmented repair compared to repair alone (P=0.003 for all flexion angles). Valgus opening was similar between UCL-transected state and repair alone (P=0.4, 0.2, and 0.1 for 30, 60, and 90 degrees). The scaffold-augmented repair did not decrease valgus opening beyond that of the native state.

Conclusion

Augmentation with a bioinductive, biocomposite absorbable structural scaffold imparts additional biomechanical strength to UCL repair alone, and restores valgus opening close to but not tighter than the native state. Use of this absorbable structural scaffold imparts time zero strength in the setting of ligament repair. Return to play timelines may still be longer than suture tape augmentation, but use of a bioabsorbable scaffold with more physiologic mechanical properties alleviates the risk for stress shielding, over-constraint, and biocompatibility concerns.