Side-to-differences of medial elbow anatomy adaptations in youth throwing athletes

Background: Injuries to the medial elbow are common in overhead sports, with the most common occurring at the medial/ulnar collateral ligament (UCL). Injury to the UCL is associated with elbow joint laxity which tends to develop over time in athletes who place their elbows under chronic valgus forces like those present during throwing. 27, 37 This instability is well documented in professional, collegiate, and high school athletes. Purpose: The purpose of this study was to investigate the medial elbow joint width and common flexor tendon thickness in the arms of youth baseball players. The hypotheses were (1) the medial elbow joint space would be greater on the dominant arm compared to the non-dominant arm in a resting position, (2) the medial elbow joint space would be greater on the dominant arm compared to the non-dominant arm in the stressed position; and (3) the common flexor tendon would have a greater thickness on the dominant arm compared to the non-dominant arm. Methods: Six participants were included in this investigation.. The width of the medial elbow was measured on ultrasound images of the medial elbow and common flexor tendon. The medial elbow joint space was measured at rest and with an applied valgus stress. Results: There was no significant difference in medial elbow joint space width between the dominant and non-dominant sides at rest or with an applied valgus stress. There was no significant difference in common flexor tendon thickness at the elbow between the dominant and non-dominant sides within subjects. The mean medial elbow joint space width at rest was 3.39mm ± 0.96mm on the dominant side and 3.47mm ± 0.87mm on the non-dominant side. When a valgus stress was applied, the dominant side mean increased to 3.92mm ± 1.02mm and the non-dominant side increased to 4.04mm ± 1.04mm. The mean flexor tendon thickness was 3.8mm ± 0.54 on the dominant side and 3.92mm ± 0.59mm on the non-dominant side. Conclusion and Practical Significance: No side-to-side difference in medial elbow joint space width or flexor tendon thickness was observed in youth baseball/softball athletes. These findings are expected in youth throwers due to their relative inexperience with overhead throwing and lack of accumulated stress on the medial elbow. Maintaining the stability of the elbow as youth throwing athletes age is a vital step in preventing costly injury later in their careers