Analysis of factors influencing fragment displacement in greater tuberosity fractures: the number of involved facets as a key risk factor

Fragment displacement is a key determinant of treatment strategy and functional outcomes in isolated greater tuberosity (GT) fractures. However, the relative contributions of fracture morphology and shoulder dislocation to displacement remain unclear. This study aimed to identify factors associated with fragment displacement, with a particular focus on facet involvement, fracture type, and the presence of shoulder dislocation using three-dimensional computed tomography (CT). Secondary displacement during nonoperative management was also explored. We retrospectively analyzed 102 shoulders (mean age 64.5 &#xb1; 14.5 years) with isolated GT fractures, including shoulders with and without anterior dislocation. Using three-dimensional CT images obtained at the time of injury, fracture morphology was evaluated based on the number of rotator cuff attachment facets (superior, middle, and inferior) and fracture type, classified as avulsion, split, or depression. Fragment displacement was defined as &#x2265;5 mm translation in any direction and was assessed on postreduction CT in dislocation cases. Associations between fragment displacement, fracture morphology, and the presence of dislocation were analyzed using chi-square tests and multivariate logistic regression. Secondary displacement during follow-up was evaluated in nonoperatively managed shoulders using standard radiographs. Overall, 65 shoulders (63.7%) exhibited &#x2265;5 mm displacement. Displacement correlated significantly with the number of involved facets (P < .001), fracture type (P = .008), and dislocation (P = .011). In the displaced group, 3 facets were involved in 49 shoulders, compared with only 8 in the nondisplaced group. Multivariate logistic regression identified facet count as the strongest independent factor (odds ratio [OR] 7.72; 95% confidence interval 3.06-19.44; P < .001). Compared with avulsion-type fractures, depression-type fractures showed a significantly lower risk of displacement (OR 0.05; 95% confidence interval 0.005-0.415; P = .006). Dislocation was associated with displacement on univariate analysis but did not remain an independent predictor after adjustment (OR 3.01; P = .071). Among 34 nonoperatively managed shoulders, secondary displacement occurred in 4 cases and was more frequently observed in fractures involving 3 facets and in split-type fractures. Fragment displacement in GT fractures is most strongly associated with the number of involved facets, suggesting that the extent of rotator cuff attachment has a major influence on fragment stability. Although dislocation was associated with an increased risk of displacement, facet morphology was the decisive determinant. CT-based assessment of facet involvement provides valuable information for understanding displacement risk in GT fractures.