BACKGROUND & OBJECTIVE
Dancers are likely to require superior function of their deep hip external rotator muscles due to the foundational use of hip external rotation or ‘turnout’ in dancing. Enhanced function of the deep external rotators may also be required when structural integrity of the hip joint is impaired by damage to the ligamentum teres or acetabular labrum, capsular laxity or acetabular undercoverage (dysplasia). The obturator internus (OI) and externus (OE) muscles both have capsular attachments and orientations that suggest a role in hip joint stability. The aims of this study were to compare size of OI and OE in dancers and matched non-dancing athletes, and to examine the relationship between hip pain and obturator size.
33 professional ballet dancers were age and sex-matched with non-dancing athletes (18 females each; mean age 27 years). Non-dancing athletes played tennis, netball or basketball from at least ten years of age and were still playing at least three times per week.
Average cross-sectional area (ACSA) of OI and OE was measured by a blinded examiner from three consecutive slices of a pelvic Magnetic Resonance Imaging (MRI) scan. The pain subscale of the Copenhagen Hip and Groin Outcome Score (HAGOS) was used, ranging from 100 (no pain) to 0 (extreme pain), and dichotomised into those with hip pain (scoring < 100) and without pain (scoring 100). Scores of ≤ 80 and > 80 were also compared between groups.
Mean OE ACSA, adjusted for height and weight, was on average 14% larger in dancers than non-dancing athletes, while OI ACSA was similar. Low levels of pain were reported in both groups (median HAGOS pain score 100: interquartile range 90-100),