Biomechanical function of surgical procedures for acromioclavicular joint dislocations

Purpose: Surgical procedures for treatment of acromioclavicular (AC) joint dislocation replace the coracoclavicular (CC) ligaments to minimize motion, allow scarring, and increase the subsequent stability of the joint. The purpose of this study was to evaluate the biomechanical function of the surgically repaired or reconstructed (CC Sling, Rockwood Screw [DePuy Orthopaedics, Warsaw, IN], and Coracoacromial [CA] Ligament Transfer Construct) AC joint after AC joint dislocation. Type of Study: A cadaver study using a convenience sample. Methods: Twelve cadaveric shoulders were tested using a robotic/UFS testing system. Three external loading conditions (anterior, posterior, or superior load of 70 N) were applied to intact and surgically repaired or reconstructed AC joint. The resulting kinematics of the AC joint and in situ forces in the CC ligaments or surgical constructs was determined. Results: For the CC Sling, anterior and posterior translation significantly increased by 110% and 330% in response to an anterior and posterior load, respectively. However, the posterior translation for the Rockwood Screw significantly decreased by 60%. Anterior, posterior, and superior translation for the CA Ligament Transfer Construct significantly increased by 110%, 360%, and 100%, respectively. The coupled translations also significantly increased for the CC Sling and CA Ligament Transfer Construct in response to all loading conditions. In contrast, the coupled translations for the Rockwood Screw tended to decrease. Furthermore, the in situ forces increased significantly for all 3 surgical constructs compared with the intact CC Ligaments in response to an anterior and posterior load. Conclusions: At time zero, increases in the primary and coupled motion for the CC Sling and CA Ligament Transfer Construct could comprise the initial healing period prescribed for AC joint dislocation. Our findings also suggest that the Rockwood Screw provides a highly rigid fixation and may explain the complications frequently seen in clinical practice. Clinical Relevance: Current surgical procedures do not have the appropriate stiffness to restore the stability of the intact joint before healing. Therefore, our results may lead to the design and development of new repairs, reconstructions, and rehabilitation protocols for AC joint dislocation.