Residual deformity after treatment of pediatric femur fractures with flexible titanium nails

Introduction: Procurvatum or anterior bow deformity is a potential complication after treatment of femur fractures with flexible titanium nails (FTNs). This article reports on a clinical evaluation of angulation after treating pediatric femur fractures with FTNs. The article also reports on a complementary investigation of potential causes of these deformities using a biomechanical model. Methods: All pediatric femoral shaft fractures treated with FTNs over a 4-year period were reviewed. Fracture location, pattern, angulation, and nail shoe tip orientation were recorded from postoperative radiographs. Malunion was defined as greater than 10 degrees of angulation on the AP radiograph or greater than 15 degrees on the lateral view. As an adjunct to the clinical study, a synthetic femur model was created using midtransverse fractures. These femurs were nailed using 2 FTNs inserted so as to create constructs having the following combinations of nail shoe tip orientation: both anterior (AA), both posterior (PP), both neutral (NN), or 1 anterior and 1 posterior(AP). The resulting angular deformities noticeable upon gross inspection were then measured. Results: Of the 70 fractures reviewed, malunion occurred in 16 fractures, of which 11 had increased anterior bow. A majority of malunions was observed in older children with middle third of the femur fractures. They were significantly more prevalent in transverse fractures compared with all other fracture patterns. Clinically, increased anterior bowing did not occur if 1 of the nails was positioned to resist procurvatum, as seen in the lateral radiograph. Depending on nail tip orientation, the biomechanical femur fracture model showed significant differences in mean deformations after nail placement: AA had 12.6 degrees of posterior bow compared with 14.8, 3.7, and 0.3 degrees of anterior bow for PP, NN, and AP, respectively. Conclusion: Anterior bowing greater than 15 degrees is the most common malunion noted in this series of femur fractures that were nailed using FTN's. We conclude that final nail shoe tip orientation influences the likelihood of anterior bow deformity. The likelihood of large anterior bowing may be reduced if at least 1 of the nails is inserted with the tip pointing in an anterior direction.