The effect of canal fill on paediatric femur fractures treated with titanium elastic nails

PURPOSE: Traditional teaching for fixation of paediatric femur fractures recommends 80% nail diameter/medullary canal diameter ratio (ND/MCD) for successful maintenance of reduction. Prior studies have investigated this with stainless steel Enders nails. Our aim was to assess the impact of ND/MCD on maintenance of reduction and malunion rates in paediatric femur fractures treated with flexible intramedullary nails (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. Patients with co-morbidities affecting bone quality were excluded. Patients were subdivided into groups based on ND/MCD. RESULTS: A total of 66 patients met inclusion criteria. Mean ND/MCD was 76.3% (32.9% to 98.8%, SD 14.3). In all, 50% (n = 33/66) of patients had > 80% ND/MCD, and only 13.6% (n = 9/66) of patients had less than 60% ND/MCD. When controlling for fracture stability, ND/MCD had no correlation with mean shortening (p = 0.07) There was no correlation between ND/MCD and angulation in the sagittal (p = 0.96) or coronal plane (p = 0.20). Three patients fit malunion criteria. ND/MCD for these patients were 40%, 67% and 79%. CONCLUSION: There was no correlation between ND/MCD and shortening or malangulation. The majority of patients in this series with less than 80% fill with FIN healed within acceptable parameters. LEVEL OF EVIDENCE: III.