The TightRope Study: a Cadaveric, Biomechanical Comparison of Generations of Suspensory Fixation with Internal Brace for Rockwood Grade V Acromioclavicular Joint Injuries

Background: Surgical treatment of Rockwood grade V acromioclavicular (AC) joint injuries remains varied. We hypothesized that the addition of a second suspensory device between the clavicle and coracoid would yield superior biomechanical results over a single device. We also hypothesized that the addition of an internal brace across the AC joint to a suspensory device would yield superior results over the suspensory device in isolation. Methods: A total of 24 cadaveric shoulders were dissected and randomized to 4 groups with 4 different constructs implanted: group A, single AC TightRope (Arthrex Inc.); group B, double AC TightRope; group C, single Knotless AC TightRope (Arthrex Inc.); group D: single Knotless AC TightRope with AC InternalBrace ligament augmentation (Arthrex Inc.). These were then loaded in a robotic arm (SIMVITRO), where 250 cycles of 50 N of force in the superior plane was applied. Dynamic creep, displacement, translation, and stiffness were assessed. Results: Testing was successfully completed for all specimens. There were no failures due to fracture or translation of the clavicle >5 mm from the starting position. Reduction was maintained with a mean superior displacement of 1.7 mm (+/- 1.4 mm). The mean peak-to- peak displacement, superior and posterior translation, dynamic creep, and stiffness did not differ significantly between the construct groups. Conclusion: This study did not demonstrate any significant biomechanical differences between groups in terms of displacement, translation, creep, or stiffness.