The Effect of the Lateral First Metatarsal Head Shape on Hallux Valgus in Forced Turnout in Pre-Pointe Female Ballet Dancers: A Pilot Study.

Background: A rounded lateral first metatarsal head shape is associated with higher rates of hallux abducto valgus recurrence following corrective surgery; however, the effect of the lateral first metatarsal head shape on the hallux abduction angle (HAA) has not yet been explored in a nonpathologic, pre-pointe ballet dancer population. The primary purpose of this study was to investigate the effect of the lateral first metatarsal head shape on the HAA when pre-pointe female dancers force their turnout.

Methods: Seventeen female, pre-pointe ballet students (mean age, 10.8 ± 0.95 years) participated in this study. Fluoroscopic images of each dancer's dominant foot were taken, and the lateral first metatarsal head shape was classified visually. Each dancer performed three consecutive stances of natural double-leg upright posture: both functional and forced turnout. HAAs were obtained by marking medial bony landmarks on paper and were compared to photographic measurements.

Results: No significant difference was found between the round and angular lateral first metatarsal head shape for the change in HAA from natural double-leg upright posture to forced turnout. Hallux abduction angle significantly increased by 4.6° (P < .001) in forced turnout compared to the natural double-leg upright posture for the photographic method, whereas the paper method demonstrated an increase of 2.6° (P = .007). No statistical differences were found between the paper and photographic methods in measuring the HAA for all stances.

Conclusions: Our findings suggest no association between the HAA and lateral first metatarsal head shape; however, HAA does increase when a dancer assumes forced turnout. The paper method demonstrated similar reliability to the photographic method and shows the potential for future use as a clinical tool in assessing hallux abducto valgus.