Dynamic Ultrasonography of Anterior Femoral Translation: Comparison to Ballet Turnout and Hip Symptoms in Dancers

Abstract

PURPOSE: To determine if there is a relationship between turnout, self-reported hip symptoms, and femoral head anterior translational motion under dynamic ultrasound in a population of adolescent ballet dancers. METHODS: Cross-sectional cohort study. Population: 25 ballet academy students, 17 females and 8 males, ages 14-18 yrs. Dynamic ultrasound of the bilateral hips was performed on each study participant in supine position. With the low frequency linear ultrasound probe in sagittal oblique plane, the distance between the femoral head and acetabular rim was measured in 3 positions: both hips in neutral position, ipsilateral hip in neutral and contralateral hip hyperflexed, and with the ipsilateral hip in extension and external rotation and the contralateral hip hyperflexed. Compensated turnout was defined as difference between functional turnout angle in first position and total bilateral hip passive external rotation in prone. Each participant completed the Hip Osteoarthritis and Outcome Score (HOOS) questionnaire. RESULTS: Spearman’s rho correlation coefficient (r) was used to test strength of association between variables, defined as <0.3 = poor, 0.3-0.5 = fair/moderate, 0.5-0.7 = good, >0.7 = strong. P=0.05 was used as threshold for statistical significance. IBM SPSS software (version 23, SPSS, Chi, IL) was used for all analyses. Mean maximal femoral translation distance for the right hip: 0.66mm (+/- 1.74mm), and the left hip: 1.56mm (+/- 1.93mm). Mean compensated turnout: 62.8° (+/- 14.8 °). There was no significant correlation between femoral translation and HOOS scores, nor between femoral translation and compensated turnout (right: p=.56, r=0.123, left: p=.203, r= -0.64). There was a significant correlation between greater compensated turnout and higher mean bilateral HOOS scores, with strongest association in the domains: symptoms (p=.02, r=.463), quality of life (p=.003, r=.561) and activities of daily living (p=.034, r=.426). CONCLUSIONS: In this population of adolescent ballet dancers, there was no significant correlation between femoral head translational motion on ultrasound and compensated turnout or self-reported symptoms. There was significant correlation between degree of compensated turnout and more favorable self-reports on hip symptoms and function.