Time-driven activity-based costing comparison of intramedullary nails versus locking plates for proximal humerus fractures: what is the primary cost driver?

Objectives The purpose of this study was to compare the day-of-surgery (DOS) costs between intramedullary nails and locking plates implants and identify independent predictors of total DOS cost using time-driven activity-based costing (TDABC). Methods A retrospective review of patients who underwent open reduction and internal fixation (ORIF) for proximal humerus fractures between 2022 and 2025 across two large metropolitan healthcare systems. Patients treated with intramedullary nail fixation were matched 1:1 to patients treated with locking plate fixation based on Neer classifications to ensure comparable fracture morphology. The primary outcome was total DOS cost and secondary outcomes included implant cost, operative duration, and postoperative outcomes. Results A total of 92 patients (46 matched pairs) were included in final analysis. On paired univariate analysis, plate fixation demonstrated significantly higher implant, direct DOS, indirect DOS, and total DOS costs compared to nail fixation (all p ≤ 0.013). In multivariate mixed effect model (R 2 = 0.362; p < 0.001), intraoperative duration emerged as the strongest independent predictor of total DOS costs (β = 23.23 per minute; p < 0.001). Institutional site was also independently associated with cost (p = 0.013). Fixation type and patient characteristics were not independently associated with total DOS cost after adjustment. Conclusion Although plate fixation demonstrated higher unadjusted DOS costs compared to nail fixation, fixation construct was not independently associated with total DOS cost after adjusting for operative time, institutional site, and patient factors. Operative time emerged as the primary driver of cost variation, suggesting that operative efficiency rather than implant selection alone determines intraoperative economic value in proximal humerus fracture fixation.