Walz, L; Salzmann, GM; Fabbro, T; Eichhorn, S; Imhoff, AB
The anatomic reconstruction of acromioclavicular joint dislocations using 2 TightRope devices: a biomechanical study.
BACKGROUND: For the reconstruction of acromioclavicular (AC) joint separation, several operative procedures have been described; however, the anatomic reconstruction of both coracoclavicular ligaments has rarely been reported. PURPOSE: The aim of this biomechanical study is to describe a new procedure for anatomic reconstruction of the AC joint. STUDY DESIGN: Controlled laboratory study. MATERIALS AND METHODS: Forty fresh-frozen cadaveric shoulders were tested. Cyclic loading and a load-to-failure protocol was performed in vertical (native, n = 10; reconstructed, n = 10) and anterior directions (native, n = 10; reconstructed, n = 10) on 20 AC joints and repeated after anatomic reconstruction. Reconstruction of conoid and trapezoid ligaments was achieved by 2 TightRope devices (Arthrex, Naples, Florida). Dynamic, cyclic, and static loading until failure in vertical (n = 5) and horizontal (n = 5) directions were tested in native as well as reconstructed joints in a standardized setting. RESULTS: The native coracoclavicular ligaments in static load for vertical force measured 598 N (range, 409-687), elongation 10 mm (range, 6-14), and stiffness 99 N/mm (range, 67-130); static load for anterior force was 338 N (range, 186-561), elongation 4 mm (range, 3-7), and stiffness 140 N/mm (range, 70-210). The mean maximum static load until failure in reconstruction for vertical force was 982 N (range, 584-1330) (P =.001), elongation 4 mm (range, 3-6) (P < .001), and stiffness 80 N/mm (range, 66.6-105) (P = .091); and for anterior static force 627 N (range, 364-973) (P < .001), elongation 6.5 mm (range, 4-10) (P = .023), and stiffness 78 N/mm (range, 46-120) (P = .009). During dynamic testing of the native coracoclavicular ligaments, the mean amount of repetitions (100 repetitions per stage, stage 0-100 N, 100-200 N, 200-300 N, etc, and a frequency of 1.5 Hz) in native vertical direction was 593 repetitions (range, 426-683) and an average of 552 N (range, 452-683) load until failure. In vertical reconstructed testing, there were 742 repetitions (range, 488-893) (P = .222) with a load until failure of 768 N (range, 486-900) (P = .095). In the anterior direction load, the native ligament failed after an average of 365 repetitions (range, 330-475) and an average load of 360 N (range, 307-411), while reconstructed joints ended in 549 repetitions (range, 498-566) (P = .008) with a load until failure of 547 N (range, 490-585) (P = .008). In all testing procedures, a preload of 5 N was performed. CONCLUSION: The anatomic reconstruction of the AC joint using TightRope is a stable and functional anatomic reconstruction procedure. The reconstruction technique led to favorable in vitro results with equal or even higher forces than native ligaments. CLINICAL RELEVANCE: Through anatomic repair, stable function of the AC joint can be achieved in an anatomic manner.