Extreme hip motion in professional ballet dancers: dynamic and morphological evaluation based on magnetic resonance imaging.

OBJECTIVE: To determine the prevalence of femoroacetabular impingement (FAI) of the cam or pincer type based on magnetic resonance imaging (MRI) in a group of adult female professional ballet dancers, and to quantify, in vivo, the range of motion (ROM) and congruence of the hip joint in the splits position.
MATERIALS AND METHODS: Institutional review board approval and informed consent from each volunteer were obtained. Thirty symptomatic or asymptomatic adult female professional ballet dancers (59 hips) and 14 asymptomatic non-dancer adult women (28 hips, control group) were included in the present study. All subjects underwent MRI in the supine position, while, for the dancers, additional images were acquired in the splits position. Labral abnormalities, cartilage lesions, and osseous abnormalities of the acetabular rim were assessed at six positions around the acetabulum. A morphological analysis, consisting of the measurement of the α angle, acetabular depth, and acetabular version, was performed. For the dancers, ROM and congruency of the hip joint in the splits position were measured.
RESULTS: Acetabular cartilage lesions greater than 5 mm were significantly more frequent in dancer's hips than in control hips (28.8 vs 7.1%, p = 0.026), and were mostly present at the superior position in dancers. Distribution of labral lesions between the dancers and the control group showed substantially more pronounced labral lesions at the superior, posterosuperior, and anterosuperior positions in dancers (54 lesions in 28 dancer's hips vs 10 lesions in 8 control hips). Herniation pits were found significantly more often (p = 0.002) in dancer's hips (n = 31, 52.5%), 25 of them being located in a superior position. A cam-type morphology was found for one dancer and a retroverted hip was noted for one control. Femoroacetabular subluxations were observed in the splits position (mean: 2.05 mm).
CONCLUSION: The prevalence of typical FAI of the cam or pincer type was low in this selected population of professional ballet dancers. The lesions' distribution, mostly superior, could be explained by a "pincer-like" mechanism of impingement with subluxation in relation to extreme movements performed by the dancers during their daily activities.