Neglected acromioclavicular joint injury in coracoid process fractures: a retrospective cohort study

INTRODUCTION: Coracoid process fractures are frequently associated with injuries to the superior suspensory shoulder complex, including the acromioclavicular (AC) joint. However, concomitant AC joint injuries may be overlooked in the acute phase, potentially limiting treatment options. This study aimed to investigate the association between coracoid process fractures and SSSC injuries and to identify imaging-based predictors of concomitant AC joint injury. METHODS: A retrospective single-center cohort study including 60 patients with coracoid process fractures was conducted between February 2016 and April 2023. Coracoid fractures were classified based on anatomical location, and associated SSSC injuries were categorized according to the involved structures. These injuries were evaluated using 3D shoulder CT. Morphological deformity of the SSSC was assessed by measuring the glenoclavicular distance (GCD)-a longitudinal parameter-on final follow-up clavicle AP radiographs. In base fractures, the medial displacement gap was measured on sagittal CT. Statistical analyses included logistic regression and ROC curve analysis to identify predictors of AC joint injury. RESULTS: Among the 60 patients, fractures were located anteriorly in 27 cases, in the middle region in 5 cases, and at the base in 28 cases. AC joint injury was identified in 15 patients, all of whom had base-type fractures. Logistic regression analysis revealed a significant association between base fractures and SSSC injuries (OR = 21.0, p < 0.001). The GCD was significantly different between affected and contralateral sides in base fracture cases (Kruskal-Wallis test, p < 0.001). Receiver operating characteristic (ROC) curve analysis indicated that a displacement gap of ≥ 5.82 mm was predictive of concurrent AC joint injury (AUC = 0.741). CONCLUSIONS: Coracoid process base fractures are significantly associated with injuries to other components of the SSSC. In particular, a displacement gap of 5.82 mm or more suggests a higher likelihood of previously unrecognized AC joint injury. LEVEL OF EVIDENCE: III, retrospective cohort study.