An In Vitro Study Demonstrating the Significance of Acromioclavicular Ligament Repair in Restoring Horizontal and Rotational Acromioclavicular Joint Stability

Background: The principle of joint reconstruction surgery is to try to recreate the native joint biomechanics and stability. With respect to acromioclavicular joint (ACJ) surgery, much focus to date has been on restoring the superoinferior stability. There is concern that persistent horizontal instability following ACJ reconstruction could lead to poorer patient outcomes; therefore, we evaluated whether acromioclavicular (AC) ligament repair offers improved horizontal stability in conjunction with ACJ reconstruction. Methods: A whole-body human cadaver was used. The ACJ was exposed and subjected to a constant 70N load on the lateral end of the clavicle to test the anteroposterior (AP), superoinferior (SI), and horizontal pivot angle (HPA) around the ACJ. The AC and coracoclavicular (CC) ligaments were subsequently divided, and the above three parameters were re-tested. Ligament augmentation and reconstruction system (Corin Group, Cirencester, UK), LockDown (LockDown Medical Limited, Redditch, UK), Endobutton (Smith and Nephew Inc., London, UK), and Neoligament implant (Xiros Ltd., Leeds, UK) were used to reconstruct the CC ligaments and tested with and without AC repair. Results: The native ACJ allowed an average 2.48 mm AP and 3.88 mm SI translation with a 27 degrees HPA. All synthetic implants significantly improved the vertical stability of the ACJ but allowed up to a four-fold increase in AP translation. Coupled with ACJ repair, all the reconstructions were far superior, especially in restoring horizontal stability. Conclusion: The implants varied in their approach to fixation and concentrated primarily on the reconstruction of CC ligaments. Our study was able to demonstrate that AC repair significantly improves the stability of the construct and significantly reduces vertical and horizontal instability.