Background: Ulnar nerve dislocation is an under-reported cause of medial elbow mechanical symptoms in baseball players. It is often accompanied by a "pop" during the throwing motion. This mechanical symptom is often confused with ulnar collateral ligament (UCL) injury. This study evaluated associations of asymptomatic ulnar nerve subluxation with UCL laxity in collegiate baseball players.
Hypothesis: Asymptomatic ulnar nerve dislocation is prevalent among collegiate baseball players, and associated with years of playing baseball, playing as a pitcher, and having medial UCL laxity.
Study design: Cross-sectional study.
Level of evidence: Level 4.
Methods: Healthy, asymptomatic, National Collegiate Athletic Association Division I, male, collegiate baseball athletes were evaluated with dynamic stress ultrasound imaging for ulnar nerve dislocation and UCL laxity, and associations with demographic and athletic variables were evaluated.
Results: A total of 50 male athletes were evaluated (mean age, 20.5 years; 40% pitchers; mean playing experience, 15.7 years). Ulnar nerve dislocation was found in 16% of players (8 of 50 players) and in 11% of elbows evaluated (11 of 100 elbows; bilateral dislocations were identified in 3 players). None of the players reported ulnar nerve symptoms. No demographic or athletic variables, including years of playing or position, were associated with dislocation (P > 0.05). Players with ulnar nerve dislocation demonstrated higher values for all sonographic UCL laxity measurements than those who did not dislocate, including 0.6 mm greater valgus stress ulnohumeral joint space and 0.4 mm greater joint space gap. However, these group differences did not reach statistical significance (P > 0.05).
Conclusion: Ulnar nerve dislocation can be an asymptomatic finding in baseball athletes. Ulnar nerves may be more prone to dislocate in the presence of medial elbow valgus laxity.
Clinical relevance: Ulnar nerve dislocation should be considered a cause of medial elbow mechanical symptoms, even if the athlete is asymptomatic.
Keywords: UCL; baseball; ulnar collateral ligament; ulnar nerve instability; ultrasound.