Comparison of Cyclic Fatigue Mechanics between UCL Repair with Internal Bracing and UCL Reconstruction

OBJECTIVES: UCL reconstruction has become the preferred treatment for UCL injury in elite throwers desiring a return to throwing. Prior reports of UCL repair demonstrated poor results in professional pitchers, with rate of return to the same or higher level pitching between 0% and 63%. (1,3,6,9,11) However, in young athletes without chronic attritional UCL damage, recent data shows reliable and rapid return to sport with primary UCL repair.(2,12,14) We previously introduced a novel UCL repair technique consisting of primary UCL repair, augmented with a spanning tape anchored at either end of the native ligament. Compared to UCL reconstruction, this construct demonstrated significantly greater resistance to gap formation, even at low cycles of valgus loading.(8) The purpose of the current study was to compare the high-cycle fatigue mechanics of augmented UCL repair versus modified Jobe UCL reconstruction. We hypothesized that the repaired specimens would have less gap formation compared to the reconstruction group after 10, 100, and 500 cycles of valgus loading. METHODS: Twenty fresh-frozen cadaveric upper extremities (10 matched pairs) were dissected to expose the anterior band of the UCL.(3) The humeral and ulnar insertions of the UCL were identified and marked to measure ligament displacement.(7) Each specimen was potted and mounted on a mechanical test frame.(4,5,8,10,13) A 2 N-m valgus preload was applied to the native elbow followed by a 60 s hold and 500 cycles of valgus loading between 2 N-m and 10 N-m. A longitudinal split in the anterior band was created and the distal attachment of the sublime tubercle was released, simulating a distal avulsion tear of the UCL. Ten cycles were repeated in this torn state. Each pair was randomly separated into either a repair or a reconstruction group (Fig 1). Each specimen was then manually subjected to 100 cycles of flexion-extension range of motion to simulate early rehabilitation protocols. The specimens were again loaded for 500 cycles between 2 N-m and 10 N-m, followed by a ramp to failure at a rate of 1°/s. Torque and rotation were recorded in addition to gap measurements for the 10(th), 100(th), and 500(th) cycle of the intact and repair/reconstruction conditions. Gaps were measured optically(8) as the change in distance of the two anatomical landmarks between the pre-cycling hold and the peak of the cycle of interest. A two-way ANOVA with repeated measures was used to detect overall differences in addition to post-hoc t-tests and Tukey’s HSD for between the two procedures and three conditions, respectively. Significance was set at p ≤ 0.05. RESULTS: The repair group showed greater resistance to gapping compared to reconstruction after 10 (p=0.008), 100 (p=0.02), and 500 (p=0.004) cycles (Fig. 2) of valgus motion. There was no difference in the intact state; however, the repair group did exhibit a reduction (p=0.007) in gap in the torn state after 10 cycles. CONCLUSION: In this preliminary report, UCL repair using internal bracing is more resistant to gap formation under fatigue loading than the gold standard reconstruction technique. The time-zero failure properties of this repair technique are on par with those of traditional reconstruction, although similar differences also seen in the torn state at early cycles may act as a confounding factor. In young throwers with insertional UCL injuries, our UCL repair technique may provide a suitable alternative to reconstruction with similar biomechanical properties and faster return to sport.