Improved intramedullary nail interlocking in osteoporotic bone.
OBJECTIVE
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.


METHODS
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).


RESULTS
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.


CONCLUSIONS
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.
Cartilege Biomechanics Group, AO/ASIF Research Institute, Clavadelerstrasse, CH-7270 Davos-Platz, Switzerland.
K
K
Ito
R
R
Hungerbühler
D
D
Wahl
R
R
Grass
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001858:Bone Nails; D002102:Cadaver; D005260:Female; D005264:Femoral Fractures / Q000209:etiology / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D007719:Knee Joint / Q000601:surgery*; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000150:complications* / Q000473:pathology; D012680:Sensitivity and Specificity