Factors associated with maintaining reduction following locking plate fixation of proximal humerus fractures: a population-based retrospective cohort study

BACKGROUND: Loss of reduction (LoR) can occur after locking plate fixation of proximal humerus fractures (PHFs). This study determined biomechanical features of fracture fixation associated with preventing LoR postoperatively. One-year reoperation rates were also compared between those with/without LoR. METHODS: Population-based administrative data for 359 adults treated using a locking plate for PHF between 2010 and 2016 were examined. Two trained assessors reviewed standardized shoulder radiographs. LoR (Yes/No) was defined as any fracture displacement >0.5 cm, and/or >10° change in neck-shaft angle (NSA) alignment relative to intraoperative imaging. Multiple logistic regression assessed how the following affected maintaining reduction: (1) sex, (2) age, (3) Neer classification, (4) shaft impaction (SI), (5) shaft medialization (SM), (6) calcar reduction (CR), (7) NSA alignment, and (8) screw use. RESULTS: LoR was seen in 79 (22%) patients. LoR was significantly associated with increasing age (odds ratio [OR] = 1.06/yr, P < .001), fracture severity (4-part vs. 2-part fracture; OR = 4.63, P = .001), and varus NSA alignment (<125° vs. ≥145°: OR = 5.6, P = .02; <125° vs. 125-145°, OR = 2.2, P = .02]). Patients achieving simultaneous SI, SM, and CR were significantly less likely (OR = 0.009, P < .001) to lose reduction, after controlling for age, fracture severity, and NSA alignment. If only SI was achieved, patients were still significantly less likely to lose reduction relative to achieving none of these mechanical features (OR = 0.17, P = .006). Reoperations were higher when LoR occurred (n = 26/77 [33.4%]) compared with no LoR (n = 20/276 [7.2%]) (P < .001). CONCLUSIONS: SI was strongly associated with preventing LoR in patients treated using a locking plate for PHF. SI with concurrent SM, CR, and a neutral or valgus NSA had the lowest rates of LoR. LoR was associated with higher rates of reoperation.