Return‐to‐Play Outcomes After Primary Ulnar Collateral Ligament Reconstruction Vary Substantially Depending on Return Criteria: A Systematic Review Stratified by Competition Level

PURPOSE: To determine how return definitions influence return to play (RTP), return to the same level of play (RTSP), advancement rates, and return timelines after primary ulnar collateral ligament reconstruction (UCLR) in baseball pitchers across levels of competition. METHODS: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, PubMed and Embase were searched from January 2000 to January 2025. Studies evaluating baseball pitchers undergoing primary UCLR and reporting RTP, RTSP, advancement, or return timing outcomes with participation-based (RTP based on a single event) or durability-based (RTP after sustained participation over a predefined threshold) criteria were included. Primary outcomes were RTP, RTSP, and advancement rate (progression to a higher level after UCLR); secondary outcome was return time stratified by return criteria. Risk of bias was assessed with the Methodological Index for Non-randomized Studies and Risk Of Bias in Non-randomized Studies of Interventions tools. RESULTS: Twenty-four studies met inclusion. Across these studies, 19 included Major League Baseball players (2194 players), 5 included Minor League Baseball (MiLB) players (2318 players), 4 included collegiate athletes (553 athletes), and 6 included high school athletes (258 athletes). RTP/RTSP rates were 86% to 92%/70% to 87% in high school, 84%/67% to 92% in college, 76.3% to 79%/69.1% to 100% in MiLB, and 80% to 97.2%/28.1% to 87% in Major League Baseball. Advancement was 55.7% to 63.2% in high school, 4.1% to 44.4% in college, and 22.3% to 45% in MiLB. Surgery-to-return time using the common RTSP definition ranged from 13.7 to 20.5 months (Major League Baseball), 14.6 to 16.4 (MiLB), and 11 to 17 (college and high school). Durability-based definitions were not consistently associated with longer return intervals. CONCLUSIONS: Without standardized return criteria, reported RTP, RTSP, advancement rates, and return timelines after primary UCLR in baseball pitchers varied substantially across studies and competition levels. Durability-based criteria were not consistently associated with longer return timelines, indicating that return outcomes should be interpreted according to the competition level and return definition used. Standardized, tier-specific return criteria may improve clinical interpretation after primary UCLR. LEVEL OF EVIDENCE: Level IV, systematic review of Level II to IV studies.