A surrogate long-bone model with osteoporotic material properties for biomechanical testing of fracture implants

Abstract

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.

Far Cortical Locking Can Reduce Stiffness of Locked Plating Constructs While Retaining Construct Strength

“…This model consisted of a 27-mmdiameter and 2-mm-thick cortex made of reinforced epoxy and a trabecular core machined from 10 pcf (0.16 g/cm 3 ) solid rigid polyurethane foam (Pacific Research Laboratories). Previous research demonstrated that five structural properties of this bone surrogate (torsional rigidity and strength, bending rigidity and strength, and screw pull-out strength) matched the lower 16% of the cumulative range reported for cadaver femora 25 . Therefore, this osteoporotic bone surrogate reflected the diminished structural properties seen in osteoporotic femora.…”

“…For the evaluation of implants in weak bone, a validated model of the osteoporotic femoral diaphysis was used 25 . This model consisted of a 27-mmdiameter and 2-mm-thick cortex made of reinforced epoxy and a trabecular core machined from 10 pcf (0.16 g/cm 3 ) solid rigid polyurethane foam (Pacific Research Laboratories).…”

Effects of Construct Stiffness on Healing of Fractures Stabilized with Locking Plates

“…Subsequently, the constructs were tested to failure in each loading mode under progressive dynamic loading to determine their strength. Finally, failure tests were repeated in a validated model of an osteoporotic femoral diaphysis 45 to determine construct strength in a worst-case scenario of bridge-plate fixation in osteoporotic bone. Each loading mode and construct was tested in five specimens.…”

The Evaluation of Pullout Tests of An Expandable Newly Designed Screw

“…These factors are the screw thread, screw design, self-tapping/non-self-tapping screws, coating of the screw, unicortical or bicortical insertion 2,5,6 .…”

“…Various factors affect it. These factors are the bone features, screw diameter, screw type, predrilling and tapping 2 .…”