Description
Objectives: Recently, the importance of the acromioclavicular (AC) ligament as well as the coracoclavicular (CC) ligament in the treatment of AC joint dislocation has been reported. Augmentation by InternalBrace® (Arthlex) for the AC ligament is one of the options for the surgical procedure of AC dislocation. However, the anchor insertion to the clavicle and the acromion in the proper position is technical demanding due to the narrow bone width and the complex bone morphology, especially in the acromion. The purpose of this study was to investigate the ideal position for the anchor insertion in the clavicle and the acromion using reconstructed CT images. Methods: Thirty shoulders in twenty-two traumatic cases who visited our emergency department and for whom a whole-body CT with a slice of 1 mm thickness was performed were included in this study . Patients with fracture and osteoarthritic changes around the AC joint were excluded. The axial, sagittal and coronal CT images of the AC joint were reconstructed by SYNAPSE VINCENT® (Fuji Film) . AC joint augmentation using InternalBrace® was simulated that the artificial ligament was inserted from the posterior part of the clavicle through the center of AC joint to the anterolateral edge of the acromion . The distance from the AC joint to the anterolateral edge of the acromion, the anterior-posterior (AP) and vertical width of the acromion at this point were measured using SYNAPSE VINCENT. Similarly, the distance from AC joint to the posterior part of the clavicle, the AP and vertical width at this point were measured. The correlation between the physical characteristics and the measured values was investigated. Results: The simulated position for the anchor insertion of the posterior clavicle was located at average 15.8mm from the AC joint, with an average AP width of 17.6 mm and an average vertical width of 7.5 mm. The distance from the AC joint to the anterolateral edge of the acromion was average13.7 mm. the AP and vertical width at the anterolateral edge was average 33.0 mm and averaged 5.6 mm, respectively. The height was weakly correlated with the vertical width of the clavicle. The AP width of the acromion was positively correlated with height and had a weakly positive correlation with weight. Conclusions: For the artificial ligament passing through the center of AC joint, the ideal range of distance from AC joint was 13.7mm at the acromion and 15.8mm at the clavicle. Although there is a concern about the pullout strength, considering the AP (17.6 mm) and vertical clavicle widths (7.5mm) , the smaller diameter anchors should be used. In the acromion with the narrow vertical width, regardless of physical characteristics, the position and direction were more limited than the clavicle, even for the small anchor.
