Bone union of the transferred coracoid graft is the key factor affecting the extent of postoperative graft changes and the clinical results following the modified Bankart and Bristow procedure: a computed tomography scan study

BACKGROUND: The extent of postoperative changes in the coracoid process grafted during the modified Bankart and Bristow procedure remains unclear. The purpose of the present study was to quantify the postoperative changes in bone surface area as assessed on computed tomography, as well as to clarify the impact of such changes on the clinical results. METHODS: Twenty-three shoulders of 21 subjects who underwent the modified Bankart and Bristow procedure were retrospectively analyzed. Computed tomography images were obtained immediately after surgery and at the final follow-up. The changes in bone surface area of the grafted coracoid process were measured on computed tomography slices in the proximity of the screw bore. Clinical outcomes were evaluated in terms of the Rowe, Walch-Duplay, and simple shoulder test scores. RESULTS: Bone area increased in 15 shoulders (65.2%) and decreased in eight shoulders (34.8%). Bone area increased by 51.3% in shoulders with bone union in the superior part of the coracoid process graft, with no significant differences between the superior and inferior sides of the graft regarding the rate of change in bone surface area (41.4% vs. 68.9% increase). However, in shoulders with bone union in the inferior part of the coracoid process graft, the rate of change in bone area differed significantly between the superior and inferior sides of the graft, exhibiting a 42.3% decrease on the superior side and 39.8% increase on the inferior side. In shoulders with no bone union, bone area decreased by 29.5% (17.4% vs. 39.3% decrease on the superior and inferior side, respectively), whereas the Rowe and Walch-Duplay scores were significantly lower than those noted in shoulders with bone union. CONCLUSIONS: Postoperative bone formation and bone resorption in the coracoid process grafted during the modified Bankart and Bristow procedure depend on whether and where bone union occurs. Graft non-union is associated with inferior clinical results.