OTA 2005 Posters
Scientific Poster #62 Basic Science
Nail Fixation of Distal Third Pediatric Femoral Shaft Fractures: Retrograde Insertion Increases Stiffness in Bending but Not Axial Torsion
Purpose: Femoral shaft fractures are among the most common reasons for pediatric orthopaedic hospital admissions. Elastic stable intramedullary nailing (ESIN) has rapidly become the treatment of choice for these patients. The most common recommendation for pediatric distal third femoral shaft fractures is antegrade nail insertion. However, studies have shown clinical success with retrograde insertion. The purpose of this study was to determine if the stability of fixation constructs differs by antegrade versus retrograde insertion.
Methods: Ten synthetic composite adolescent-sized femur models and 20 flexible titanium (Ti) intramedullary (IM) nails were equally divided into antegrade and retrograde groups. A simulated transverse fracture was created in each of ten models in the distal third of the shaft. The fractures were then stabilized with ESIN. The specimens were subjected to mechanical tests, 4-point bending followed by axial torsion, using a materials test system (MTS TestWorks 4: Instron 4464). Bending moments were applied to the medial aspect of the model across the fracture site at a rate of 0.05 mm/sec to a maximum displacement of 3.7 mm (7°). Torsional moments were applied to the distal aspect of the model in internal and then external rotation at a rate of 0.75°/sec to a maximum of 10°. Each test consisted of five cycles; the fourth cycle was analyzed. Loads and stiffness were determined between consistent displacement limits; differences were compared using t-tests (a=0.05, two-tailed).
Results: Bending stiffness (see chart below) was significantly greater in the retrograde group [350 N/mm (± 2)] compared to antegrade [195 N/mm (± 95)]. A 66-kg load placed across the fracture displaced the site 3.7 mm for the antegrade group, while the retrograde group required a load 89% greater (125 kg) Torsional stiffness differences were not statistically significant.
Conclusion/Significance: This study calls into question previous recommendations for antegrade fixation of distal third femur fractures. Retrograde insertion offers clear biomechanical advantages.