Radiographic outcomes of the humeral stem after treating a proximal humerus fracture with an uncemented reverse total shoulder arthroplasty: a multicenter retrospective review

Background Reverse total shoulder arthroplasty (rTSA) for proximal humerus fractures is becoming more common. The aim of this study was to investigate the radiographic outcomes of uncemented rTSA for proximal humerus fractures and compare these outcomes based on three different implants. Materials and Methods This was a retrospective review of patients treated with uncemented primary rTSA for acute proximal humerus fracture at two large healthcare institutions using one of three different humeral stem designs. Group A (n = 46) received a Zimmer TM stem, Group B (n = 27) received a DJO Altivate stem, and Group C (n = 18) received a Medacta stem for a total of 159 patients. Three independent reviewers assessed the most recent x-rays for 1) humeral subsidence, 2) humeral tilt, 3) humeral radiolucent lines, 4) humeral stem at risk for loosening, 5) osteolysis, 6) humeral stress shielding, 7) component failure, 8) spot welds, 9) scapular notching, and 10) tuberosity union. Results Mean follow-up was 21 months (range, 6 months to 10 years). Average age at time of surgery was 71.0 years old. Radiographic analysis showed Group C (67%) was associated with significantly higher rates of stress shielding compared to Group B (19%) and Group A (6.5%) (p < 0.001). Two Group C patients (11%) and one Group A patient (2.2%) met criteria for a humeral stem at risk of loosening, a finding not observed in Gorup B (p > 0.9). A logistic regression model further confirmed that Group C stems were independently associated with increased odds of stress shielding (OR = 28.667; 95% CI: 6.229 – 131.924; p < 0.0001) compared to Group A, whereas Group B stems were not significantly different than Group A (OR = 3.258; 95% CI: 0.712 – 14.906; p=0.128). There were 4 cases of postoperative instability, three of which involved humeral loosening and required revision surgery (two from Group B and one from Group C). One patient experienced a periprosthetic humerus fracture 8 years postop, and another patient underwent several revision surgeries for periprosthetic joint infection, both from Group A. None of the three groups demonstrated significant subsidence or scapular notching. Conclusion Overall, we found significant variability in radiographic performance, particularly regarding stress shielding and risk of stem loosening when evaluating radiographic outcomes of these three cementless humeral stem designs used in reverse total shoulder arthroplasty for proximal humerus fractures.