Mechanisms of ulnar collateral ligament injury in baseball: criteria and rationale for return to play — a systematic review

Return-to-play (RTP) readiness is a critical consideration for common baseball injuries, including after ulnar collateral ligament (UCL) injuries. UCL injuries, often resulting from repetitive throwing stress, can significantly impact an athlete’s career, requiring interventions ranging from nonoperative rehabilitation to surgical reconstruction. While RTP criteria for these injuries exist, they remain inconsistent across studies and clinical practice. Commonly reported RTP criteria include achieving pain-free range of motion and completion of progressive throwing distances. This systematic review aims to analyze and compare different RTP criteria for UCL injuries in baseball players. This systematic review follows the PROSPERO protocol (CRD42024607322) and adheres to the PRISMA guidelines. Three independent reviewers conducted a comprehensive search across PubMed, Scopus, and Embase to identify relevant studies. Search results were imported into Covidence for systematic screening and data management. Any disagreements or uncertainties in study selection were resolved by a fourth reviewer to ensure consistency and accuracy. After full-text screening and eligibility assessment, 18 articles were included for data extraction. Eighteen studies on UCL injuries (n = 2887) were included. UCL injuries predominantly affected professional or collegiate pitchers in baseball and were linked to valgus stress during high-velocity throwing. Reported rehabilitation protocols varied, ranging from brief immobilization followed by progressive range-of-motion and throwing programs to structured three-month conservative interventions before considering surgery. RTP was assessed using objective performance metrics such as earned run average (ERA), walks and hits per inning pitched (WHIP), and advanced metrics like Wins Above Replacement (WAR). RTP rates ranged from 80% to 91%, with most players returning to their pre-injury level of competition. Some studies reported incomplete protocol adherence due to pain, lack of motivation, or pursuit of alternative treatments. This review highlights inconsistencies and differences in RTP criteria for UCL injuries. Key influencing factors include treatment type, competition level, and psychological readiness. Although metrics such as ERA, WHIP, and imaging findings are frequently used, their application lacks uniformity. Standardized, multidisciplinary RTP protocols integrating physical, imaging, and psychological components are essential to guide safe and objective return-to-sport decisions.