Introduction
While injuries to the ulnar collateral ligament (UCL) of the elbow have conventionally been treated with surgical reconstruction techniques, direct repair of the UCL has gained popularity in recent years. Some prior studies have also reported the use of an internal brace to augment the UCL repair, in an effort to protect the native ligament while maintaining valgus stability during the healing process. The initial clinical results of this technique have been promising, with 92% of athletes returning to the same level of competition (or higher) at an average of just 6.7 months postoperatively. However, the appropriate amount of tension that should be placed on the internal brace device remains unknown in the context of UCL repair. Overtensioning the repair construct could theoretically lead to increased ulnohumeral contact pressures, while undertensioning could lead to excessive stress on the healing UCL. Thus, the aim of the present study was to determine the optimal tension of the internal brace in a cadaveric, biomechanical model of augmented UCL repair.
Methods
Six matched pairs of fresh-frozen cadaveric upper extremities were used in this study. Biomechanical testing was performed using a previously-validated model. The intact UCL was first tested under a valgus load of 10 Nm. The UCL was then transected from its distal attachment at the sublime tubercle to simulate an avulsion injury. An internal brace-augmented UCL repair was performed using high-strength suture tape and 3.5mm biocomposite suture anchors, as previously described by Dugas and colleagues. Valgus loading at 10 Nm was performed with the internal brace in three different states of tension - high tension (IB Tight), medium tension (IB Medium), and low tension (IB Loose). The amount of ulnohumeral displacement and the amount of strain across the repair construct were calculated for each testing state. One-way ANOVA analysis was used to compare strain and ulnohumeral gap formation between groups.
Results
Under 10 Nm of valgus stress, the mean gap formation of the intact UCL was 31.14 ± 6.79 mm and the mean strain was 0.07 ± 0.13. All internal brace tension states (IB Tight, IB Medium, and IB Loose) demonstrated significantly greater mean strain and mean ulnohumeral gap formation compared to the native UCL control (p < 0.05 for all comparisons). Moreover, there were no significant differences in mean strain or mean ulnohumeral gap formation between the IB Tight (Strain: 0.13 ± 0.13, Gap: 32.56 ± 6.41 mm), IB Medium (Strain: 0.16 ± 0.13, Gap: 33.58 ± 6.68), and IB Loose (Strain: 0.17 ± 0.12, Gap: 33.78 ± 6.26) tension states (p > 0.05 for all comparisons).
Conclusions
No differences were observed between internal brace tension states with regard to strain or ulnohumeral gap formation, and all UCL repair constructs (regardless of internal brace tension) were biomechanically inferior to the intact native UCL. These data suggest that the amount of tension placed on the internal brace does not have a substantial effect on the biomechanical integrity of the UCL repair construct at time zero. Thus, our findings may support placing the internal brace under less tension, thereby maintaining an equivalent biomechanical effect while avoiding the potential for elbow cartilage damage due to increased ulnohumeral contact pressures.