Adolescents with Low Body Mass Index Are More Vulnerable to Pediatric Nondisplaced Femoral Neck Fractures.

Background: Femoral neck fracture is a rare condition among fractures in the pediatric population. However, its potential for grave complications such as avascular necrosis or severe limb length discrepancy warrants prompt diagnosis and management. Much effort has been made to assess fracture risk in young adolescents in relation to obesity, low vitamin D levels, or young age osteoporosis. However, to our knowledge, there has been no literature that highlights a higher incidence of femoral neck fracture in adolescents with low body mass index (BMI).

Methods: At a level I trauma center, 22 early adolescents aged 10 years and older who had femoral neck fractures and underwent surgical treatment were included in the study. At the time of injury, BMI of each patient was stratified into 5 categories (underweight, normal weight, overweight, moderate obesity, and extreme obesity) based on BMI for age. Underweight was defined as a BMI below the 5th percentile, normal weight as between the 5th and 85th percentile, overweight as between the 85th and 95th percentile, and obese as above the 95th percentile. Then the patients were divided into 2 groups according to trauma degree: high-energy trauma and low-energy trauma. Low-energy fractures were defined as those caused by all types of trauma except for accidents involving motor vehicles, bicycles, or ski and all falls from greater than standing height. Independent samples t-tests and Pearson's chi-square tests were conducted between the 2 trauma groups.

Results: Excluding 2 patients lost to follow-up, 4 of 13 patients (30.77%) in the low-energy fracture group were underweight, whereas none in the high-energy fracture group were underweight. Including valgus impacted femoral neck fractures, 7 femoral neck fractures were nondisplaced, while 13 were complicated with displacement and required closed reduction. Avascular necrosis was observed in 4 cases and limb length discrepancy in 3 cases. The mean BMI percentile differed statistically significantly between the 2 trauma groups (p < 0.05).

Conclusions: Low-energy femoral neck fractures in adolescents appeared to be associated with low BMI. Future studies are required to clarify the relationship between low BMI and fracture risk.