Advanced Bone Age in Children With Blount Disease: A Case-Control Study Sanjeev Sabharwal, MD, MPH, Sara M. Sakamoto, MD, and Caixia Zhao, MD 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 out- comes such as persistent valgus overcorrection after proximal tibial osteotomy in children with early-onset Blount disease and undercorrection after guided growth treatment among adoles- cents 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/m 2 in the Blount disease group and 23 kg/m 2 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 dis- crepancy 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 dis- ease 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. Key Words: Blount disease, body mass index, bone age, skeletal maturity, chronologic age (J Pediatr Orthop 2013;33:551–557) B lount disease is a developmental disorder primarily affecting the proximal tibial growth plate. Based on whether the lower limb deformity is first noted before or after the age of 4 years, authors have classified Blount disease as either early-onset or late-onset, respectively. 1 Examination of the affected child often reveals a multi- planar deformity along with shortening of the affected lower extremity. 2 Although the etiology of Blount disease is likely multifactorial, a strong association with child- hood obesity has been observed. 3,4 Excessive compressive forces to the postero-medial aspect of the proximal tibia may contribute to the varus, procurvatum, and internal tibial torsion. 2,5 The prevalence of obesity is increasing worldwide and has reached epidemic proportions. Obesity affects approximately 17% of all children and adolescents in the United States, triple the rate from the previous gen- eration. 6 Childhood obesity is also associated with an earlier onset of puberty, 7 with some investigators re- porting advanced bone age in heavier children compared to their normal weight peers. 8–10 The goal of treatment in Blount disease is to restore lower limb alignment and equalize the leg length dis- crepancy. Given the concern of recurrent deformity after surgical realignment, a few authors have recommended valgus overcorrection in these children with early-onset disease in anticipation of the limited growth potential of the “sick” medial proximal tibial physis. 11–13 Although such overcorrection may decrease the possibility of re- current varus deformity, if the patient has advanced skeletal maturity, the iatrogenic genu valgum may persist into adulthood. Such valgus alignment, especially in obese children with a large thigh girth appears quite awkward, alters kinematics during gait, and is generally not well tolerated. 14,15 As a case in point, an 8+11-year- old obese female [body mass index (BMI), 40.4] presented to our outpatient facility with previously untreated bi- lateral genu varum, right side worse than left (Fig. 1), that was initially noted by the family around age 2 years. Radiographic evaluation done at the time of presentation was consistent with early-onset Blount disease (Fig. 2). Given the concern with recurrent deformity due to her From the New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ. None of the authors received financial support for this study. The authors declare no conflict of interest. Reprints: Sanjeev Sabharwal, MD, MPH, Department of Orthopedics, UMDNJ-New Jersey Medical School, 90 Bergen Street, Doctor’s Office Center, Suite 7300, Newark, NJ 07103. E-mail: sabharsa@ umdnj.edu. Copyright r 2013 by Lippincott Williams & Wilkins ORIGINAL ARTICLE J Pediatr Orthop  Volume 33, Number 5, July/August 2013 www.pedorthopaedics.com | 551