Characterization of the torsional structural properties of feline femurs and surrogate bone models for mechanical testing of orthopedic implants

Abstract

Objective: To characterize the torsional structural properties of the feline femur and design a bone model surrogate for mechanical testing of feline orthopedic implants. Study design: Experimental. Sample population: Paired feline femurs (n = 30) and bone models (8 materials, n = 4/group).Methods: Femurs were cyclically tested nondestructively in torsion and then loaded to failure. A generic femoral model was then designed from native femur dimensions and tested similarly by using 1 of 8 materials that were 3-dimensionally printed or machined. Outcome measures consisting of torsional compliance, angular deformation (AD), and torque to failure were compared by using Student's t test (P < .05). Failure modes are reported as descriptive statistics. Results: Torsional compliance (1.6 AE 0.3 /Nm, 2.0 AE 0.1 /Nm), AD (3.1 AE 0.6 , 3.8 AE 0.2 ) and torque to failure (7.8 AE1.2 Nm, 8.1 AE 1.3 Nm) did not differ between feline femurs and short-fiber epoxy (SFE) models. Conversely, most printed materials displayed excessive TC and failed by plastic deformation (AD > 15-fold that of native femurs) rather than by fracture. Feline bone and SFE both failed by spiral fractures. Conclusion: None of the outcome measures differed between the 4th generation SFE model and cadaveric femurs, but differences were identified between feline bone and printed materials. Clinical impact: Machined SFE can be used to create a surrogate bone model with torsional structural properties similar to those of feline femurs. In contrast, common printable materials appear unsuitable to produce a realistic feline bone surrogate.

Evaluation of a Feline Bone Surrogate and In Vitro Mechanical Comparison of Small Interlocking Nail Systems in Mediolateral Bending

“…This was an expected finding since the SFE material we used had previously been validated as a suitable bone surrogate for both human 29 and canine bone, 4 and more recently as a FBS in torsion. 3 While previous reports have used SFE to evaluate the mechanical behaviour of implants, those studies were conducted using hollow cylindrical rods. In contrast, the shape, dimensions and polyurethane filled epi-metaphyses of our FBS were intended to mimic clinically relevant implant application during bridging osteosynthesis.…”

“…The bending structural properties of native feline femurs were compared with those of the previously designed FBS. 3 In Part 2: A diaphyseal fracture gap model 20 was created to evaluate the mechanical properties of six construct variations stabilized using one of six implants (Groups 1-4, 6 and 7, n ¼ 4/group). Implants included the I-Loc 3 and 4mm nails, Targon 2.5 and 3.0 mm nails, as well as LCP 2.0 and 2.4mm.…”

“…Using a precision digital caliper (Mitutoyo America Corporation, Aurora, Illinois, United States) morphometric measurements were obtained as previously described. 3 Dissected specimens were then wrapped in saline soaked towels, placed in hermetically sealed plastic bags and frozen at -20°C until testing. Approximately 24 hours prior to testing, femurs were thawed at room temperature.…”

“…Compliance rather than stiffness was computed since testing was conducted under load control. 3,7,20,28 Outcome measures consisted of the following: Part 1 BC (degrees/Nm), AD (degrees), F M (Nm) and failure mode; Part 2 BC and AD; Part 3 F M and failure mode.…”

“…3 This FBS was designed to simulate morphometric measurements of feline long bones. 3 In another report, screw pullout force was similar between a SFE model and native feline bone. 8 Should our FBS also be validated in four-point bending, investigators could confidently perform mechanical evaluations of feline orthopaedic implants and predict clinically relevant failure modes.…”