Improved intramedullary nail interlocking in osteoporotic bone.

Abstract

Intramedullary nail locking bolts often fail to gain purchase or cut out in osteoporotic bone. The biomechanical stability of a bladelike device that lowers intraosseous stress levels by distributing the load over a greater volume of bone was compared with conventional locking bolts in osteoporotic bone. Standardized simulated comminuted supracondylar femoral fractures (segmental defect) in fresh-frozen paired osteoporotic (bone mineral density <200 milligrams per cubic centimeter) human cadaveric femurs were stabilized with a retrograde unreamed distal femoral nail and distally interlocked with conventional locking bolts or a bladelike device. The distal portions of the fixator-bone constructs were tested under axial load, and the stiffness and strength were compared (pairwise). Interlocking with a bladelike device was 41 percent stiffer (p = 0.01) and 20 percent stronger (p = 0.02) than that with conventional locking bolts. All posttesting radiographs showed compaction of the cancellous bone distal to the interlocking devices. Even after nail displacements of twelve millimeters, only a few locking bolts were plastically deformed and no bladelike device showed gross plastic deformation. This study showed the biomechanical benefits of increasing the bone-implant interface surface for improving the acute stiffness and strength of fracture fixation in osteoporotic cancellous bone. The fixator-bone construct withstood higher forces before failure in these fragile bones.