Hypothesis and BackgroundTotal elbow arthroplasty (TEA), categorized into linked and unlinked types, is commonly reported treatment for rheumatoid arthritis of the elbow. Although unlinked TEA preserves bone, it may result in instability. This study aimed to assess the outcomes of unlinked TEA in rheumatoid arthritis of the elbow beyond two years and to identify factors correlating with postoperative valgus instability of unlinked TEA. MethodsThis study included patients who underwent TEA for rheumatoid arthritis of the elbow at our department between August 2009 and January 2017, with a follow-up period exceeding two years. Elbow joint range of motion (ROM) and clinical scores were evaluated preoperatively and at the final follow-up. Factors contributing to valgus instability, such as the Larsen grade, sex, age, side, preoperative ROM, postoperative ROM, implant placement, preoperative carrying angle, and the use of biological disease-modifying antirheumatic drugs (bDMARDs), were also assessed. ResultsThis study encompassed 26 elbows from 23 patients, with a mean patient age at surgery of 64.8 years and a mean follow-up duration of 92.4 months. Significant improvements were observed in the ROM (extension: from -31° preoperatively to -21° postoperatively [p = 0.02], flexion: from 116°–137° [p < 0.001]), Japanese Orthopaedic Association-Japan Elbow Society Elbow Function Score (from 45.9–86.3 points [p < 0.001]), and Mayo Elbow Performance Score (from 43.6–91.7 points [p < 0.001]). At the last follow-up, two elbows exhibited radiolucent lines around the humeral stem, whereas seven had valgus instability. Factors correlated with valgus instability included total arc at the final follow-up, preoperative carrying angle, and the use of bDMARDs. Discussion and ConclusionUnlinked TEA demonstrated favorable midterm outcomes for rheumatoid arthritis of the elbow, albeit with occasional valgus instability. Surgeons should consider preoperative carrying angle and bDMARD use, and exercise caution regarding intraoperative extensions.