Ultrasonographic Prevalence of Ring-Down Artifact in the Medial Elbow Joint Gap at the Valgus Position in Asymptomatic High School Baseball Players

Abstract

Objectives: Repetitive valgus stress during pitching in baseball can lead to medial elbow instability. Although ring-down artifact (RDA) has been considered an indicator of valgus instability, its pathological significance remains unclear. This study aimed to clarify RDA-positive rates and differences in valgus conditions in the medial elbow joint gap distance of asymptomatic high school baseball players.

Methods: Sixty-nine high-school students underwent ultrasonography to visualize the medial elbow joint gap distance. Individuals with linear hyperechoic images in the medial elbow joint gap distance were classified as RDA-positive, while those without were classified as RDA-negative. Measurements were conducted under three conditions: at rest (nongravity condition), with gravity-induced forearm valgus load (gravity condition), and with a ball grip in addition to the gravity condition (ball-grip condition). McNemar's test was conducted to compare changes in RDA-positive rates within each group under the three conditions for the pitching and nonpitching sides. The Student t test was conducted to compare medial elbow joint gap distance in RDA-positive and negative groups under the gravity condition.

Results: On the pitching side, RDA-positive rates significantly increased from 51.5% to 83.8% from nongravity condition to gravity condition and significantly decreased to 13.2% in ball-grip condition (P < .01). Similarly, on the nonpitching side, RDA-positive rates significantly increased from 44.1% to 55.9% between nongravity condition and gravity condition and significantly decreased to 14.7% in ball-grip condition (P < .01). RDA-positive rates were significantly higher on the pitching side than on the nonpitching side in gravity condition (P < .01). However, no significant differences were found in quantitative medial elbow joint gap distance between the RDA-positive (4.4 ± 0.9 mm) and RDA-negative groups (4.1 ± 0.9 mm) under gravity condition (P = .39).

Conclusion: RDA-positive rates in asymptomatic high school baseball players increased under gravity condition and decreased under ball-grip condition, but no significant difference was observed in quantitative medial elbow joint gap distance between RDA-positive and -negative groups. As such, RDA positivity may not be a specific indicator of valgus instability in gravity condition.

Keywords: baseball injury; dynamic stabilizer; medial elbow joint gap; ring‐down artifact; ultrasound; valgus instability.