The effects of body mass index on treatment of paediatric femur fractures managed with flexible intramedullary nails

PURPOSE Traditionally, flexible intramedullary nails (FINs) are not to be used to fix femur fractures in patients > 50 kg (110 lbs). However, studies have not examined the efficacy of this technique in overweight and obese patients who may be under this 'weight cutoff'. The purpose of this study was to assess how patient body mass index (BMI) impacts the treatment of paediatric femur fractures managed with FINs. METHODS Retrospective data was collected on all paediatric patients treated with FINs for diaphyseal femur fractures at a single tertiary care institution over a ten-year period. BMI was calculated and categorised according to the Centre for Disease Control BMI Calculator for Children and Teens. Patients with comorbidities affecting bone quality were excluded. RESULTS A total of 54 patients met inclusion criteria. In all, 14 patients were underweight, 20 were within a normal weight range, and 20 were overweight/obese. There was no correlation between BMI and mean shortening (underweight: 7.1 mm, normal weight: 5.2 mm, overweight/obese: 7.2 mm; p = 0.55). There was no correlation between BMI and mean anterior/posterior angulation (underweight: 3.1°, normal weight: 3.8°, overweight/obese: 3.3°; p = 0.93). There was no correlation between BMI and varus/valgus angulation (underweight: -0.86°, normal weight: -0.5°, overweight/obese: -1.25°; p = 0.89). Three cases fit malunion criteria. One of these patients fell into the 'underweight' category and two patients fell into the 'normal weight' category. CONCLUSION We found no association between BMI and malunion in FIN fixation of femoral diaphyseal fractures in children. All cases of malunion were seen in underweight or normal weight patients.