Racial differences in late-onset Blount disease.

Purpose: Blount disease is most common among obese Black children. The reason for Blount's racial predisposition is unclear. Given that obesity is a risk factor for Blount disease and the known associations between race, obesity, and socioeconomic status in the United States, we hypothesized that socioeconomic status and severity of obesity differ between Black and non-Black children with late-onset Blount disease. We additionally examined differences in treatment types between Black and non-Black children.

Methods: One hundred twenty-five patients from two institutions were included. Age at presentation, age of onset, body mass index, race, sex, and treatment type were recorded. These variables were compared between Black and non-Black children. Insurance type and estimated household income were used as markers of socioeconomic status.

Results: Of the 125 patients with late-onset Blount disease, body mass index percentiles were higher for Black patients (96th ± 12th percentile) than non-Black patients (89th ± 22nd percentile) ( p  = 0.04). Black patients also had lower estimated incomes (US$48,000 ± US$23,000 vs US$62,000 ± US$30,000) ( p  = 0.01) and much higher rates of Medicaid enrollment (69% vs 24%) ( p  < 0.01) than did non-Black patients. Regarding treatment types, osteotomy was more common among Black patients (60%) than non-Black patients (38%) ( p  = 0.033).

Conclusion: The race-related associations we found between obesity and socioeconomic status suggest that non-genetic factors may contribute to observed racial differences in the prevalence of Blount disease.

Level of evidence: level III.