Complications and revisions of inlay versus onlay design for reverse shoulder arthroplasty: a meta analysis and systematic review

Reverse total shoulder arthroplasty (RTSA) is the standard treatment for rotator cuff tear arthropathy; humeral stems are classified as inlay or onlay, but their comparative risks of complications and revision remain unclear. This systematic review evaluates these outcomes to inform implant selection. This study was systematically evaluated using the Preferred Reporting Items for Systematic Evaluation and Meta-Analysis (PRISMA) guidelines. All research literature comparing the clinical outcomes of the two humeral prosthesis designs was collected by searching PubMed, Cochrane, and Embase databases. The primary outcome indicators included revision rates and complication rates including scapular notching, infection, fracture, loosening, and dislocation. Through strict inclusion and exclusion criteria, a total of 13 studies were ultimately included in the analysis, involving 16,309 patients (onlay 5680 versus inlay 3261). When comparing the inlay and onlay groups, the inlay humeral prosthesis demonstrated significantly higher rates of scapular notch complications (inlay 17.74% versus onlay 9.41%, p = 0.0008), while the onlay humeral prosthesis demonstrated significantly higher rates of infection (onlay 1.67% versus inlay 0.87%, p = 0.02). The onlay group had slightly higher rates of fracture (onlay 1.73% versus inlay 0.59%), while the dislocation rate (onlay 0.59% versus inlay 1.73%) and loosening rate (onlay 0.47% versus inlay 0.71%) were slightly higher in the inlay group. However, the differences in fracture, dislocation, loosening rates, revision rates, and American Shoulder and Elbow Surgeons Score (ASES) and visual analog scale (VAS) scores were not statistically significant ( p > 0.05). In terms of revision rates, the onlay group had a slightly higher revision rate, but this difference was not statistically significant (inlay 3.48% versus onlay 3.94%, p > 0.05). In RTSA, inlay and onlay humeral designs demonstrated subtle postoperative differences: onlay stems are associated with lower scapular notching, while inlay stems have lower infection rates. Other complications, revision rates, and ASES, VAS scores did not differ significantly.