Asymmetric bony hip morphology in asymptomatic professional baseball pitchers: a cross-sectional cohort study

BACKGROUND: Cam (femoral head asphericity) and pincer (acetabular overcoverage) morphologies at the hip are risk factors for femoroacetabular impingement syndrome and labral tears. Baseball pitchers repetitively load their hips during throwing which may place them at risk of developing cam or pincer morphology. These morphologies may develop asymmetrically as baseball pitchers load one hip more than the other during throwing. METHODS: A cross-sectional cohort study compared bilateral bony hip morphology in asymptomatic male professional baseball pitchers (n = 16) and cross-country runner controls (n = 15). Cam morphology (alpha angle at 12, 1, 2, and 3 o’clock positions), and acetabular lateral center-edge angle and version were assessed from computed tomography images of the hip in the drive leg (i.e., leg on the same side as the pitching or preferred throwing arm) and contralateral stride leg. RESULTS: Maximum alpha angle (adjusted for body mass and age) across clock positions in the drive and stride legs of pitchers was 71.7° (95%CI, 57.6° to 85.8°) and 54.3° (95%CI, 39.1° to 69.5°), respectively (adjusted p value = 0.01). There were no differences in alpha angle between legs in runners or between stride legs in pitchers and runners. Pitchers were 8.8 (95%CI, 1.5 to 36.6) times more likely to have a cam morphology (alpha angle ≥ 60°) at one or more clock positions in a hip compared to runners. There was a greater frequency of an alpha angle ≥ 60° at the 3 o’clock position in the drive compared to stride leg of pitchers (p = 0.03). The drive leg in pitchers also had a greater frequency of an alpha angle ≥ 60° at one, two, or three clock positions compared to the stride leg (all p < 0.05). The drive leg in pitchers had a lower frequency of elevated lateral center-edge angle compared to the stride leg (p = 0.03). CONCLUSIONS: Asymptomatic professional baseball pitchers exhibited a greater prevalence and larger cam morphology in the drive leg on the same side as the throwing arm compared to the contralateral stride leg. Whether the observed morphological variations have long-term consequences in terms of the development of pain and joint damage requires further investigation.