Association Between Computed Tomography-Derived Hounsfield Units of the Ulnar Collateral Ligament and Valgus Laxity in Professional Baseball Players.

BACKGROUND: Ulnar collateral ligament (UCL) insufficiency in overhead athletes is thought to result from repetitive valgus loading that induces progressive microtrauma and structural attenuation. Although stress ultrasonography and magnetic resonance imaging are commonly used to evaluate UCL integrity, no imaging modality provides a widely accepted, objective, and quantitative marker of intrinsic ligament tissue quality. PURPOSE: To determine whether nonstress computed tomography (CT)-derived Hounsfield unit (HU) values of the UCL are associated with valgus laxity in professional baseball players and whether HU values serve as a quantitative marker of UCL insufficiency. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 44 professional baseball players underwent non-contrast-enhanced CT of the dominant elbow. HU values of the anterior bundle of the UCL were measured on reconstructed oblique coronal images using polygonal regions of interest for the whole ligament as well as proximal, midsubstance, and distal thirds. Valgus laxity was assessed using stress ultrasonography (stress delta difference) and stress CT (stress delta). Associations between HU values and valgus laxity were evaluated using Spearman correlation, group comparisons, receiver operating characteristic (ROC) analysis, and multivariable logistic regression. Exploratory analyses examined relationships between HU values and age, baseball experience, and playing position. RESULTS: Lower proximal UCL HU values were significantly associated with greater valgus laxity on stress ultrasonography (r = -0.424; P = .005) and stress CT (r = -0.331; P = .030). On stress ultrasonography, whole-ligament HU values also demonstrated a significant negative association with valgus laxity, whereas midsubstance and distal HU values were not significantly related to laxity. Proximal HU values showed acceptable discrimination of increased valgus laxity (area under the ROC curve, 0.755), and ROC analysis identified an optimal cutoff of 65.5 HU with 85.7% sensitivity and 71.4% specificity. Proximal HU values remained significant after adjusting for age (odds ratio per 1-HU increase, 0.91; P = .049). Proximal HU values were not associated with age, years of baseball experience, age at baseball initiation, or playing position. CONCLUSION: CT-derived HU values of the proximal UCL were associated with valgus laxity in professional baseball players with structurally intact ligaments. A reduction in proximal HU values may reflect localized structural attenuation that is functionally relevant to medial elbow stability.