An Unusual Pattern of Acromioclavicular Joint Instability With Coracoid Base Fracture

Concurrent acromioclavicular (AC) joint dislocation and coracoid process fracture is a rare injury pattern, representing a double disruption of the superior shoulder suspensory complex (SSSC) and resulting in mechanical instability. Due to its rarity, there is no consensus on optimal management.

A 43-year-old male sustained a right shoulder injury during a snowboarding accident. Imaging revealed a right-sided AC joint dislocation with minimal superior displacement (coracoclavicular [CC] distance 13.6 mm on the right vs. 12 mm contralaterally) and a base-near coracoid fracture (Ogawa Type I and Eyres Type IV). Clinical examination showed clavicular elevation and tenderness over the AC joint, with preserved neurovascular function. Surgical management included AC joint stabilization with a short hook plate and screw osteosynthesis of the coracoid fracture. Postoperative care involved immobilization in a functional brace with staged passive and active-assisted range-of-motion exercises, progressing to strengthening from Week 12.

At 6 and 12 weeks, radiographs confirmed maintained reduction and fracture healing. The hook plate was removed 3.5 months postoperatively. Follow-up 6 weeks later demonstrated a healed coracoid base, congruent AC joint, minimal pain, and good shoulder function.

Surgical fixation restores biomechanical integrity of the SSSC and allows early functional rehabilitation. Combined AC and coracoid fixation represent a viable option, though isolated AC stabilization may also yield favorable outcomes if intraoperative imaging confirms adequate indirect reduction of the coracoid fracture. In our opinion, combined fixation provides a very stable construct with the best chances for anatomical healing and restoration of SSSC integrity.

Concurrent AC dislocation and coracoid fracture is a rare injury that requires careful diagnostic assessment, as the coracoid fracture may be overlooked on conventional imaging. This case demonstrates that surgical management with AC stabilization using a hook plate and coracoid screw fixation can achieve excellent radiological and clinical outcomes.