Will this proximal humeral fracture displace during conservative treatment? A validation study of previously defined risk factors

Conservative management is the treatment of choice for non-displaced proximal humeral head fractures; however, a recent study reported that 25.2% of these fractures subsequently displace to a degree necessitating surgical intervention. In this study, we evaluated and externally validated clinical and radiological risk factors in a new patient cohort. From June 2018 to December 2020, 113 patients treated conservatively for isolated proximal humeral fractures were included. Mean age was 70 years (range 29 to 94 years), the female-to-male-ratio was 3.2:1. Displacement was defined as translation of the humeral head of at least 10 mm on follow-up radiographs. The previously identified clinical (osteoporosis, neurological disorder, alcohol abuse) and radiological risk factors including disrupted medial hinge, a low “deltoid tuberosity index” (DTI), and a high “eccentric head index” (EHI)—describing the offset of the humeral head center in relation to the humeral shaft axis in anteroposterior and Neer views—were assessed. Secondary fracture displacement occurred in 25 out of 113 patients (22.1%). Radiological risk factors such as DTI suggesting low cortical bone quality of the proximal humerus (< 1.4, odds ratio (OR) 2.8; 95% CI 1.1–7.2; p = 0.032), a high EHI (AP or Neer > 0.4, OR 4.7; 95% CI 1.7–12.9, p = 0.003), and a disrupted medial hinge (OR 2.8; 95% CI 1.1–7.0; p = 0.030) increased the risk of secondary displacement significantly. On external validation in the new cohort, the previously developed model discriminated secondary displacement with an area under the ROC curve of 0.78 (95% CI 0.68–0.88); at a cross-validated threshold it reached a sensitivity of 68% (95% CI 46–85) and a negative predictive value of 89% (95% CI 79–95). In the new cohort, 22.1% (25/113) of conservatively treated patients showed secondary displacement of ≥ 10 mm. In this validation study, earlier defined radiological factors (DTI < 1.4, disruption of medial hinge, high EHI > 0.4) proved to be relevant predictors of secondary displacement of proximal humeral fractures.