The femoral deformity in Blount's disease: a comparative study of infantile, juvenile and adolescent Blount's disease.

An associated femoral deformity in patients with Blount's disease is not commonly described in the literature. The objective of this study is to establish the presence and magnitude of deformity in the coronal plane of the distal femur in children of all ages with Blount's disease and compare this to a matched cohort of children from the same population. This was a retrospective review of patients from an academic hospital. A control group was established by matching for age and gender from a group of unaffected patients with mid to proximal third femur fractures or controls at the same hospital. Study participants were categorized by age at onset of deformity as follows: infantile (<4 years), juvenile (4-10 years) and adolescent (>10 years). The measurements of the anatomic lateral distal femoral angle (aLDFA) were recorded and the Wilcoxon rank-sum test was used to determine statistically significant differences in the LFDA between children with Blount's disease and those without. Seventy-two Black African children were included in the study with 118 affected limbs (27 infantile, 55 juvenile and 36 adolescent). The overall average aLDFA for all patients with Blount's disease was 87° (range 73-100°). Overall, children with Blount's disease had a higher aLDFA than children without (87° vs. 82°). There was a significant association between LDFA in the control group and children with Blount's disease in each of the three groups. This study found distal femoral varus deformity to be present in all groups of children with Blount's disease. In this study population, it was most significant in the infantile and adolescent groups when compared to a control group from the same population. Although further studies are required, the surgeon must always assess the distal femoral component in treating children with Blount's disease.