Background <p>Proximal humerus fractures are common fragility fractures in older adults. Open reduction and locking plate internal fixation can restore fracture alignment and facilitate early rehabilitation; however, some patients still develop persistent night pain after surgery, potentially impairing sleep and tolerance of rehabilitation. This study aimed to analyze factors associated with persistent night pain 3 months after locking plate fixation for proximal humerus fractures and to construct a preliminary preoperative risk model and a complete risk stratification model after immediate postoperative radiographic assessment.</p> Methods <p>This single-center retrospective observational study included 331 patients with proximal humerus fractures who underwent open reduction and locking plate internal fixation at our hospital between January 1, 2021, and December 31, 2024, and had completed 3-month postoperative follow-up. The primary outcome was persistent night pain at 3 months after surgery. General clinical variables, fracture characteristics, preoperative radiographic parameters, surgical variables, immediate postoperative fixation quality, postoperative recovery, and complications were collected. Eight candidate predictors were prespecified before model development. Variable selection was performed using least absolute shrinkage and selection operator (LASSO) logistic regression with 10-fold cross-validation, and selected variables were refitted using conventional multivariable logistic regression. Model performance was evaluated using receiver operating characteristic (ROC) curves, the area under the curve (AUC), calibration curves, the Hosmer-Lemeshow test, the Brier score, decision curve analysis, 1,000 bootstrap resamples, and internal temporal split validation.</p> Results <p>Among the 331 patients, 95 had persistent night pain at 3 months after surgery, corresponding to an incidence of 28.7%. Multivariable logistic regression showed that preinjury sleep disturbance or anxiety/depression, a lower deltoid tuberosity index (DTI), greater displacement of the greater tuberosity, preoperative loss of medial support, lack of effective postoperative medial support, and plate malposition were associated with persistent night pain. The complete model had an AUC of 0.814 (95% confidence interval [CI], 0.763–0.864), a bootstrap-corrected concordance index (C-index) of 0.801, a calibration intercept of -0.012, a calibration slope of 0.946, and a Brier score of 0.154. The preoperative model had an AUC of 0.768 (95% CI, 0.710–0.825). Internal temporal split validation demonstrated stable discrimination and prediction error; in sensitivity analyses excluding major complications, using a stricter alternative outcome, and applying multiple imputation, the effect directions of the principal predictors were consistent with those in the complete-case analysis.</p> Conclusions <p>Persistent night pain 3 months after locking plate fixation of proximal humerus fractures is not uncommon. Preinjury sleep disturbance or anxiety/depression, lower DTI, greater-tuberosity displacement, medial support loss, inadequate postoperative medial support reconstruction, and plate malposition were associated with this outcome. The preoperative model may provide preliminary preoperative risk information. The complete model should be applied after immediate postoperative radiographic assessment and may help identify patients at increased risk of persistent night pain and inform targeted postoperative management. Clinical application still requires prospective, multicenter external validation.</p>