Varus Strength of the Medial Elbow Musculature for Stress Shielding of the Ulnar Collateral Ligament in Competitive Baseball Pitchers

Abstract

Purpose Valgus load opens the medial elbow compartment, causing elongation of the ulnar collateral ligament (UCL) that can eventually lead to attenuation and failure. Ideally, the muscles surrounding the medial aspect of elbow joint should coordinate medial elbow compression to prevent the medial elbow compartment from opening and loading the UCL. This study aimed to determine whether baseball pitchers have sufficient elbow varus strength to unload the UCL during pitching. Methods Using an electromagnetic tracking device, we measured the peak elbow varus moment during pitches (fastball, slider, curveball, and changeup) by 14 professional and 8 collegiate pitchers. Elbow varus strength was measured with an isokinetic dynamometer system while the medial elbow joint space was monitored using ultrasonography. A paired t-test was used to compare the peak varus moment generated during pitching with the varus strength, and the relative intensity of muscular output required to unload the UCL was determined. Results Except for curveballs, the muscular varus strength (57.5 ± 9.2 N·m) was not significantly larger (P = 0.165-0.853) than the peak varus moments during pitching (55.4 ± 13.0 N·m). Ten participants did not have sufficient muscular varus strength to completely unload the UCL from valgus loading when throwing fastballs and other pitch types. The relative intensity of muscular torque output required for stress shielding of the UCL ranged from 89.1% ±21.7% maximum voluntary isometric varus strength (MVIVS) for curveballs to 103.1% ±26.5% MVIVS for fastballs. Conclusions Our findings demonstrate that most of the valgus load on the elbow joint during pitching can be counteracted by the muscular varus moment, but valgus loading on the UCL is likely unavoidable in baseball pitching.