Background
Ulnar nerve neuropathy around the elbow is a common pathology in throwing athletes, and occurs due to many factors including valgus elbow, and ulnar nerve hypermobility. For patients with ulnar nerve neuropathy, anterior transposition of the ulnar nerve is common procedures. Meanwhile, Ulnar nerve hypermobility has been reported to be present in 2% to 47% of asymptomatic individuals. However, no studies have investigated the rate of ulnar nerve hypermobility in throwing athletes, and the relationship between ulnar nerve mobility, and clinical symptom and throwing performance. This study was designed to classify the sonographic assessment for the mobility of the ulnar nerve compared to physical evaluation, and to determine whether ulnar nerve hypermobility is associated with clinical symptoms, and throwing performance in baseball players.
Hypothesis/Purpose: We investigated ulnar nerve hypermobility using ultrasound to evaluate the relationship between the ulnar nerve hypermobility and clinical sign including throwing performance in college baseball players.
Methods
138 elbows in 69 college baseball players were examined. Each participant was queried regarding symptoms attributable to the ulnar nerve. In addition, structural measurements consisting of the tinel test and elbow flexion compression testing were examined. Sonographic examiners were, unaware of reported symptoms, independently performed a standardized examination of both elbows to assess ulnar nerve hypermobility. For sonographic assessment, the ultrasound probe was located at the medial condyle of the humerus to visualize the ulnar nerve in short-axis view in the extended elbow position. During extension to flexion of the elbow, the mobility of ulnar nerves was assessed, and categorized as stable, or hypermobile, which was further subclassified as subluxation, or dislocation. Pared t-test was used to compare the mobility of the ulnar nerve between throwing and non-throwing sides. Fisher's exact test was used to assess the relationship between physical exams and the mobility of the ulnar nerve. Values of p<0.05 were considered statistically significant.
Results
Ulnar nerve hypermobility was identified in 54 (78.3%) of the 69 elbows in throwing side. Meanwhile, hypermobility was 53 (76.8%) in non-throwing side without significant difference, compared to non-throwing side. Elbows with nerve hypermobility did not experience a higher prevalence of subjective symptoms (snapping, pain, and tingling) than did elbows with stable nerves. Provocative physical examination testing for ulnar nerve irritability, however, showed consistent trends toward heightened irritability in hypermobile nerves (p = 0.04 to 0.16). Demographic data and anatomic measurements were similar between the subjects with stable nerves and those with hypermobile nerves. Additionally, all participants did not show decrease of throwing performance.
Conclusion
Ulnar nerve hypermobility occurs in over half of the baseball players in throwing and non-throwing sides. Utilizing a standardized sonographic examination, a diagnosis of ulnar nerve hypermobility can be established with substantial interobserver reliability. In baseball players, ulnar nerve hypermobility does not appear to be associated with an increased symptomatology attributable to the ulnar nerve and throwing performance. Anterior transplantation of ulnar nerve may not be needed for baseball players with ulnar nerve neuropathy.