Retrograde Stainless Steel Flexible Nails Have Superior Resistance to Bending in Distal Third Femoral Shaft Fractures

It has been shown that retrograde titanium flexible intramedullary nails (Ti FIN) provide superior resistance to bending compared to antegrade Ti FIN in distal femur fractures. The purpose of this study was to compare resistance to torsional and bending forces of stainless steel (SS) FIN, with or without a locking screw, and Ti FIN in distal third femoral shaft fractures. We hypothesize that locked retrograde SS FIN will demonstrate greater resistance to both bending and torsional forces.

Thirty adolescent synthetic femur models were used to simulate transverse distal femoral fractures at either 60 mm or 90 mm proximal to the distal femoral physis. The femurs were instrumented with antegrade Ti FIN, antegrade SS FIN, retrograde Ti FIN, retrograde SS FIN, or retrograde locked SS FIN. Three models for each construct at both osteotomy levels were tested. Models were analyzed to determine maximum resistance to bending and torsion.

In fractures 60 mm from the physis, retrograde SS FIN demonstrated statistically superior resistance to bending when compared with both antegrade and retrograde Ti FIN (P=0.001 and 0.008, respectively) and antegrade SS FIN (P=0.0001). Locked SS constructs showed a trend towards greater resistance to bending forces when compared with unlocked constructs (P>0.05). No significant difference was seen in resistance to bending when fractures were 90 mm proximal to the distal femoral physis between the five groups. No significant differences were observed in resistance to torsion in either the proximal or distal fracture models, regardless of construct type.

Retrograde SS FIN confer significantly greater resistance to bending forces for fractures 60 mm proximal to the distal femoral physis compared with Ti FIN or antegrade entry SS FIN. In fractures 90 mm from the physis, no differences were noted in our model. Our results support the use of retrograde SS nails in the pediatric patient with distal femoral shaft fractures.

Level II-comparative biomechanical study.