Ultrasonographic appearance of the pronator quadratus muscle in high school baseball pitchers with and without elbow symptoms: a pilot study.

ABSTRACT

PURPOSE: Earlier reports have described forearm flexor muscles as active stabilizers of the elbow to valgus stress during throwing motion. The pronator quadratus (PQ) muscle acts in coordination with the pronator teres muscle for forearm pronation. This study of high school pitchers was conducted to assess the association between sonographic appearance and a history of elbow symptoms. METHODS: We examined 123 high school baseball pitchers, all of whom had completed a self-administered questionnaire, including items related to throwing-related elbow joint pain sustained during the prior year. Ultrasound examination was made of the pitchers with and without valgus stress of the medial aspect of the bilateral elbows. The sonographic appearance of the PQ was assessed on sagittal and axial images on the bilateral side. For participants with and without a history of elbow symptoms, we compared the maximum thickness of the PQ on sagittal and axial images of the throwing side. RESULTS: Regarding maximum thickness of the PQ on the sagittal and axial images, a significant difference was found between the throwing and non-throwing sides (throwing side vs non-throwing side mean sagittal 6.3 mm vs 5.7 mm, axial 8.2 mm vs 7.5 mm, 95% confidence interval sagittal 0.41-0.70, p < 0.001, axial 0.53-0.82, p < 0.001). The maximum thickness of the PQ on axial images with elbow symptoms was significantly greater than the PQ thickness of those without elbow symptoms. Nevertheless, no association was found between elbow valgus instability and the maximum thickness of the PQ on sagittal and axial images of the throwing side. CONCLUSION: Sonographic appearance of the PQ might be associated with elbow joint conditions in high school baseball players.