Biomechanics of femoral interlocking nails

Today there is a variety of different interlocking intramedullary nail desi gns available for the femur. We compared different nail types in the bone i mplant complex (BIC) of four unreamed solid nails and a slotted reamed nail with simulated comminuted mid shaft fractures to see if there are major di fferences in stiffness for axial load, bending and torsion. The fractures w ere simulated by a 2 cm defect osteotomy in paired human cadaver femora. Ea ch bone was tested intact in a universal testing machine, osteotomy and ost eosynthesis were performed, and the BIC was tested. Relative stiffness was calculated. In torque testing the unslotted solid nail showed significantly more stiffness (0.6-1.8 Nm/degrees) compared to the slotted nail (0.2 Nm/d egrees). Compared to intact bone (6.9 Nm/degrees), both groups of nails wer e significantly less stiff (relative stiffness 2-20%). In axial load and be nding testing the large diameter unreamed nail showed significantly higher stiffness (32-68%). This study shows that stiffness of bone implant complex in interlocking femoral nails is more dependent on nail profile than on th e pressfit of nails in the medullary canal. (C) 2000 Elsevier Science Ltd. All rights reserved.