A Surrogate Long-Bone Model with Osteoporotic Material Properties for Biomechanical Testing of Fracture Implants

摘要

In vitro comparative testing of fracture fixation implants is limited by the highly variable material properties of cadaveric bone. Bone surrogate specimens are often employed to avoid this confounding variable. Although validated surrogate models of normal bone exist, no validated bone model simulating weak, osteoporotic bone is available. This study presents an osteoporotic long-bone model designed to match the lower cumulative range of mechanical properties found in large series of cadaveric femora reported in the literature. Five key structural properties were identified from the literature: torsional rigidity and strength, bending rigidity and strength, and screw pull-out strength. An osteoporotic bone surrogate was designed to meet the low range for each of these parameters, and was mechanically tested. For comparison, the same parameters were determined for surrogates of normal bone. The osteoporotic bone surrogate had a torsional rigidity and torsional strength within the lower 2% and 16%, respectively, of the literature based cumulative range reported for cadaveric femurs. Its bending rigidity and bending strength was within the lower 11% and 8% of the literature based range, respectively. Its pull-out strength was within the lower 2% to16% of the literature based range. With all five structural properties being within the lower 16% of the cumulative range reported for native femurs, the osteoporotic bone surrogate reflected the diminished structural properties seen in osteoporotic femora. In comparison, surrogates of normal bone demonstrated structural properties within 23%–118% of the literature based range. These results support the need and utility of the osteoporotic bone surrogate for comparative testing of implants for fixation of femoral shaft fractures in osteoporotic bone.