Biomechanical Comparison for Unstable Femoral-supracondylar Fractures Treated with Retrograde, Traditional Femoral or Tibial Locked Nails

Retrograde locked intramedullary nailing has gradually been widely used to treat femoral supracondylar fractures. Because a standard femoral supracondylar nail has unique disadvantages: high price and potentially inducing a femoral shaft stress fracture, it is often replaced by a traditional femoral or tibial locked nail. A biomechanical comparison was therefore made between both traditional locked nails in order to recommend a better one in treating unstable femoral supracondylar fractures. Fourteen left sawbone femurs were osteotomized in the femoral supracondylar area to simulate an unstable fracture without shortening. Seven specimens were treated with retrograde dynamic traditional femoral locked nails and other seven, retrograde dynamic traditional tibial locked nails. All specimens were tested with a servohydraulic Material Testing System machine to compare the relative stability. Static compression, dynamic cyclic compression, and static compression to failure were investigated. An extensometer was used to measure displacement of fragments. Displacement between both fragments increased following increment of loads in both nails. The load-displacement curve showed nearly linear up to 1,000N for both nails. The femoral nail had a larger stiffness as compared to the tibial nail at 100 N and 200 N (p= 0.02 and 0.04, respectively) in static compression and at 700-1,000N (p= 0.01, in each case) in dynamic cyclic compression; moreover, larger loads in static compression to failure (p < 0.001).