Nailing versus plating for comminuted fractures of the distal femur: a comparative biomechanical in vitro study of three implants

Purpose

The purpose of our study was to determine the biomechanical properties of three different implants utilized for internal fixation of a supracondylar femur fracture. The retrograde supracondylar nail (SCN), the less invasive stabilization system plate (LISS) and the distal femoral nail (DFN) were tested and their biomechanical properties compared.

Methods

Twenty pairs of fresh-frozen human femura were used. Each femur was osteotomised to simulate a comminuted supracondylar fracture (AO/OTA 33.A3) and then randomized to fracture fixation with either SCN (n=9) or LISS (n=9). Each contralateral femur was stabilized with DFN as a control (n=18). Two femur pairs were spent on pretesting. All femura were subjected to axial (10–500 N) and torsional (0.1–14 Nm) loading.

Results

Eighteen matched femur pairs were analyzed. The post-loading median residual values were 49.78, 41.25 and 33.51% of the axial stiffness of the intact femur and 59.04, 62.37 and 46.72% of the torsional stiffness of the intact femur in the SCN, LISS and DFN groups. There were no significant differences between the three implants concerning axial and torsional stiffness.

Conclusions

All implants had sufficient biomechanical stability under physiological torsional and axial loading. All three implants have different mechanisms for distal locking. The SCN nail with the four-screw distal interlocking had the best combined axial and torsional stiffness whereas the LISS plate had the highest torsional stiffness.