Hallux valgus (HV) in adults is an acquired pathology related to 1^st metatarsal (M1) abduction. In children, it is related to abnormal M1 joint surface orientation.

HV deformities in children and adults differ.

Descriptive study of radiologic abnormalities in a pediatric population of symptomatic HV, with comparison to a population without symptomatic HV.

Weight-bearing X-rays were studied in pediatric patients undergoing surgery for HV and in a control population. Measurements comprised M1P1, M1M2, DMAA, DM2AA, MPAA, and sesamoid subluxation index.

Twenty-five patients (42 feet) were included in the HV group, and 16 patients (29 feet) in the control group. Mean age was 13 years in both. Interobserver reproducibility was excellent for M1P1, and good for M1M2, DMAA and DM2AA. In HV, 71% of feet showed M1M2 angle>12° and 98% DMAA>10°; DM2AA was>0°, except in 1 foot.

Normal values are the same in children and adults: M1P1<15°, DMAA<10° and M1M2<12°. In the HV group, DMAA was systematically pathological, while M1M2 was pathological in only 71% of cases. Childhood HV is related to abnormal DMAA, sometimes associated with increased M1M2 angle, especially in severe forms. DM2AA assesses distal M1 joint surface orientation with respect to the M2 axis; in the HV group, it was systematically>0° (except in 1 foot). Thus, in case of concomitant DMAA and M1M2 abnormalities, DMAA is more severely abnormal than M1M2 (DM2AA=DMAA-M1M2).

Childhood HV is mainly due to abnormal M1 joint surface orientation, sometimes associated with increased 1^st metatarsal abduction. DM2AA reflects the balance between 1^st metatarsal abduction and M1 joint surface orientation abnormality.

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