Injuries to the acromioclavicular joint usually result in pain and instability. However, few biomechanical studies have investigated the mechanism of injury and treatment. Consequently, current rehabilitation protocols and surgical techniques have similar outcomes with no “gold standard” for treatment. Therefore, the thesis objective was to evaluate the function of the intact and injured acromioclavicular joint during combined loading to provide guidelines for the development of rehabilitation protocols and reconstructions for complete dislocations.

A robotic/universal force-moment sensor testing system was utilized to apply an external load in combination with joint compression to intact and injured joint. Joint compression caused significantly decreases in primary (in the direction of loading) translations and joint contact forces while increasing coupled (orthogonal to the direction of loading) translations for the injured joint (p<0.05). These findings suggest common surgical techniques such as distal clavicle resection, which remove painful joint contact, may cause loads to be supported by other structures and be transmitted over a smaller area due to the increased coupled motion and joint contact. Both findings reinforce the importance of restoring each component of the acromioclavicular joint after injury.

Next, the cyclic behavior and structural properties of an anatomic reconstruction of the coracoclavicular ligaments were determined during uni-axial tensile testing and compared to the intact coracoclavicular ligaments. After complete dislocation of the acromioclavicular joint, the anatomic reconstruction complex was found to have significantly lower stiffness and ultimate load compared to the intact ligaments (p<0.05). However, the bending stiffness of the clavicle significantly decreased after dislocation. Consequently, the individual properties of the tendon graft used during reconstruction had more comparable results to the intact coracoclavicular ligaments than current surgical techniques.

The evaluation of the intact and injured joint during a combination of loading conditions provided guidelines for the development of an anatomic reconstruction. The experimental methodology used to evaluate the anatomic reconstruction incorporated a more realistic mechanism of failure during testing. Both studies provide insight on functional changes of the intact acromioclavicular joint following injury and reconstruction. Future investigations should quantify the loads transmitted across the joint during daily activities. Computational models could use this information in addition to data collected with the methodology developed in this thesis to optimize the proposed anatomic reconstruction.