Comparison of Functional Outcomes and Complications of Inlay and Onlay Reverse Shoulder Arthroplasty in Neer Type 4 Proximal Humerus Fractures and Cuff Tear Arthropathy: A Multicentric Study.

BACKGROUND: This multicenter retrospective study was conducted with the objective of comparing the outcomes and complications between inlay and onlay reverse shoulder arthroplasty (RSA) in patients presenting Neer Type 4 proximal humerus fractures and cuff tear arthropathy. The primary aim of this investigation was to assess and juxtapose the clinical as well as functional outcomes of individuals who underwent onlay reverse shoulder arthroplasty with those who underwent inlay reverse shoulder arthroplasty.

METHODS: A retrospective cohort study was conducted, involving patients who had undergone reverse shoulder arthroplasty between the period of 2016 and 2022. The study divided the population into two groups: Group A received inlay humeral components, while Group B received onlay humeral components. Functional outcomes were evaluated using the American Shoulder and Elbow Surgeons (ASES) and Constant scores. Range of motion, infection, periprosthetic fractures, and nerve injuries were also assessed.

RESULTS: The study included 67 patients in Group A and 62 patients in Group B. Group A had significantly better functional outcomes, as indicated by higher ASES and Constant scores ( p  < 0.05). Group A also had greater shoulder joint motion ( p  < 0.05). Periprosthetic fractures were significantly more common in Group B ( p  < 0.05). However, complication rates, including infection and instability, did not significantly differ between the groups ( p  > 0.05). Nerve injuries occurred in both groups, with slightly higher occurrence in Group B.

CONCLUSION: Inlay humeral components in reverse shoulder arthroplasty for Neer Type 4 fractures and cuff tear arthropathy resulted in better functional outcomes, increased range of motion, and lower incidence of periprosthetic fractures compared to onlay components. Onlay components showed potential advantages in reducing instability rates. Further studies with larger samples and standardized protocols are needed to confirm these findings.