Advanced bone age in children with Blount disease: a case-control study.

PURPOSE: Children with Blount disease are often obese and have muliplanar limb deformities including leg length discrepancy. Surgical options for these skeletally immature patients include guided growth and realignment osteotomy. Suboptimal outcomes such as persistent valgus overcorrection after proximal tibial osteotomy in children with early-onset Blount disease and undercorrection after guided growth treatment among adolescents with late-onset Blount disease can occur. Although obesity has been associated with precocious puberty, whether children with Blount disease have advanced skeletal maturity has not been previously investigated. We hypothesized that compared to their peers, children with Blount disease will have advanced skeletal (bone) age.

METHODS: The relationship between skeletal and chronologic age was compared between 33 patients with Blount disease (12 early-onset, 21 late-onset) and 33 age-matched and sex-matched controls. The influence of variables such as the age of onset of Blount disease and patient's chronologic age on the discrepancy between skeletal and chronologic age was also evaluated.

RESULTS: The mean body mass index was 39 kg/m2 in the Blount disease group and 23 kg/m2 in the control subjects (P<0.0001). Compared to their chronologic age, the bone age was advanced 16 months in Blount disease group (95% confidence interval, 10-22 mo) and 5 months in the control group (95% confidence interval, -1-10; P=0.003). On the basis of subgroup analysis, the bone age was advanced 26 months in early-onset and 10 months in late-onset Blount disease (P=0.01). The discrepancy between bone age and chronologic age decreased as chronologic age increased in both the control (r=-0.36, P=0.04) and Blount disease groups (r=-0.58, P=0.0004).

CONCLUSION: Compared to their peers, children with Blount disease have advanced skeletal maturity. The difference between bone age and chronologic age decreases with growth. Since advanced skeletal maturity can impact the strategy for surgical realignment and magnitude of planned (over)correction of lower limb deformity, preoperative assessment of bone age should be considered when managing children with Blount disease.

LEVEL OF EVIDENCE: Level III.