Outcomes of modular diaphyseal vs. nonmodular metaphyseal reverse total shoulder arthroplasty stem for 3- and 4-part proximal humerus fractures

Proximal humerus fractures (PHFs) are increasingly prevalent in the aging population, with reverse shoulder arthroplasty (rTSA) emerging as a preferred surgical treatment for complex fracture patterns. Recent advancements have introduced shorter, metaphyseal-fixation humeral stems as alternatives to traditional modular diaphyseal stems. However, limited data exist comparing the clinical outcomes of these designs following rTSA for PHF. A retrospective analysis of 99 patients undergoing rTSA for acute three- or four-part PHFs between 2014 and 2024 was conducted. Patients received either a modular diaphyseal stem (n = 66) or a nonmodular metaphyseal stem (n = 33). Demographics, perioperative variables, American Shoulder and Elbow Surgeons scores, visual analog scale scores, range of motion, complications, and revision rates were compared. Statistical analyses included t-tests for continuous variables and chi-squared tests for categorical data. No significant differences were observed between groups in terms of demographics, comorbidities, hospital stay, or overall postoperative complications. The modular diaphyseal cohort had a significantly longer operative time and follow-up duration. Postoperative American Shoulder and Elbow Surgeons scores were higher in the diaphyseal group (76.35 vs. 65.58, P = .015), while the metaphyseal group demonstrated superior abduction (74.55&#xb0; vs. 57.93&#xb0;, P = .0267) and external rotation (32.12&#xb0; vs. 14.79&#xb0;, P < .0001). No significant differences were found in postoperative visual analog scale scores (P = .117) or revision rates (P = 1.00). Both modular diaphyseal and nonmodular metaphyseal stem designs offer safe and effective options for rTSA following PHF, with distinct advantages. Modular stems may provide improved functional scores over longer follow-up, whereas metaphyseal stems may enhance range of motion. These findings support individualized surgical planning based on patient anatomy, functional goals, and revision risk. Further long-term studies are warranted to optimize implant selection.