Is Ulnar Collateral Ligament Strength Proportional to Height and Weight?

Abstract

Background: The rates of surgeries for ulnar collateral ligament (UCL) injuries continue to rise for baseball pitchers. The physical size of pitchers has also increased, bringing into question whether today's larger pitchers have proportionally bigger and stronger UCLs able to withstand greater elbow varus torque. Furthermore, controversy exists in biomechanics literature regarding whether kinetics during pitching should be reported as torque (in N·m) or normalized torque (scaled by body weight and height).

Hypothesis/purpose: The purpose of this study was to quantify the relationships between body size and mechanical properties of the UCL measured directly on cadaveric specimens. It was hypothesized that greater body weight and height would correlate with greater UCL strength, stiffness, and cross-sectional area.

Study design: Descriptive laboratory study.

Methods: UCL thickness and length were measured by ultrasound for 20 cadaveric right elbows from young adult (mean age, 33 ± 6 years) male donors. Each elbow was then dissected, potted, and placed into a mechanical test frame at 90° of flexion. The specimen was then tested to failure at a rate of 1° of valgus rotation per second. Correlations between geometric and biomechanical data were tested by linear regressions (P < .05).

Results: The mean UCL failure torque was 45.0 ± 10.5 N·m, and the mean stiffness was 2.72 ± 0.48 N·m/deg. Correlations between failure torque and height (P = .25), weight (P = .85), and height × weight (P = .72) were nonsignificant. Similarly, stiffness showed no significant correlation with height (P = .24), weight (P = .21), or height × weight (P = .18). UCL cross-sectional area did not significantly correlate with body height (P = .34), height × weight (P = .064), or weight (P = .065).

Conclusion: Body size is not correlated with UCL strength and stiffness.

Clinical relevance: Clinicians should not assume that bigger athletes have a stronger UCL. Furthermore, elbow varus torque during throwing for adult athletes should not be normalized by body weight and height.