Correlation of body mass index and radiographic deformities in children with Blount disease.

BACKGROUND

Children with Blount disease tend to be heavier than their peers; however, the relationship between the magnitude of obesity and the severity of limb deformities in Blount disease has not been well studied.

METHODS

A retrospective review of the preoperative medical records and radiographs of patients with previously untreated Blount disease was conducted. Demographic information including gender, ethnicity, the age when deformity was first noted, the age at the examination, and the body mass index was recorded. Frontal and sagittal plane deformities were analyzed by one examiner using full-length standing radiographs. The association of body mass index with various demographic and deformity parameters was then analyzed.

RESULTS

Over an eight-year period, forty-five patients with sixty-five limbs affected by Blount disease were identified. Seventeen children (twenty-seven limbs) had early-onset Blount disease, and twenty-eight children (thirty-eight limbs) had late-onset disease. Fifteen of the children with early-onset disease and twenty-six of those with late-onset disease were overweight. There was no significant relationship between body mass index and gender, ethnicity, or laterality. The children with early-onset disease tended to have a lower body mass index but a greater magnitude of radiographic deformities compared with the children with late-onset disease. Greater varus malalignment (r = 0.74, p < 0.0001) and tibial procurvatum (r = -0.79, p = 0.002) were noted with an increasing body mass index in the early-onset, but not the late-onset, group of patients. Irrespective of the age at onset, the correlation of body mass index with frontal and sagittal plane deformities was stronger in extremely obese children (body mass index of > or =40).

CONCLUSIONS

There is a significant relationship between the magnitude of obesity and biplanar radiographic deformities in children with the early-onset form of Blount disease and in those with a body mass index of > or =40. These clinical findings are consistent with the literature concerning the effect of compressive forces on growth at the proximal tibial physis.

LEVEL OF EVIDENCE

Prognostic Level II.