Biomechanical Evaluation of an Augmented Coracoacromial Ligament Transfer for Acromioclavicular Joint Instability

Abstract

The purpose of this study was to establish and biomechanically evaluate an augmented coracoacromial ligament (CAL) transfer technique that eliminates the biomechanical drawbacks of the conventional Weaver-Dunn procedure and restores the intact joint kinematics. The acromioclavicular joints of 12 human shoulder specimens were tested for anterior, posterior, and superior translation during cyclic loading as well as for stiffness and ultimate tensile strength in a subsequent load-to-failure protocol. After luxation, the specimens were randomly assigned to 2 treatment groups: CAL transfer and polyester-augmented CAL transfer. For the coracoclavicular augmentation, a strong 1-mm polyester loop was intertwined between 2 flip buttons for coracoid and clavicle fixation. Only the medial half of the CAL was transferred and fixed in a medialized position at the clavicle. Translational testing showed significantly higher anterior (12.1 mm), posterior (9 mm), and superior (13.4 mm) translation for the CAL transfer technique as compared with the native joint (5.4 mm, 3.3 mm, and 3.4 mm, respectively) and the modified augmented CAL transfer procedure (6.2 mm, 4.2 mm, and 3.6 mm, respectively) (P < .05). No significant differences were found between the intact acromioclavicular joint and the augmented CAL transfer regarding anterior and superior translation. Posterior translation was significantly higher for the augmented CAL transfer compared with the native joints (P = .033), but the quantitative difference was small (0.8 mm). The augmented CAL transfer using the medial half of the CAL and supplementing it with a strong 1-mm polyester loop intertwined between 2 flip buttons for coracoid and clavicle fixation has been shown to restore anterior and superior translation of the native acromioclavicular joint. The promising biomechanical in vitro results must be interpreted in the context of clinical investigations regarding the risk of bony erosion resulting from the use of permanent suture material.