title: Mechanical analysis of a rodent segmental bone defect model: the effects of internal fixation and implant stiffness on load transfer.
abstract: Segmental bone defect animal models are often used for evaluating the bone regeneration performance of bone substituting biomaterials. Since bone regeneration is dependent on mechanical loading, it is important to determine mechanical load transfer after stabilization of the defect and to study the effects of biomaterial stiffness on the transmitted load. In this study, we assess the mechanical load transmitted over a 6mm femur defect that is stabilized with an internal PEEK fixation plate. Subsequently, three types of selective laser melted porous titanium implants with different stiffness values were used to graft the defect (five specimens per group). In one additional group, the defect was left empty. Micro strain gauges were used to measure strain values at four different locations of the fixation plate during external loading on the femoral head. The load sharing between the fixation plate and titanium implant was highly variable with standard deviations of measured strain values between 31 and 93% of the mean values. As a consequence, no significant differences were measured between the forces transmitted through the titanium implants with different elastic moduli. Only some non-significant trends were observed in the mean strain values that, consistent with the results of a previous finite element study, implied the force transmitted through the implant increases with the implant stiffness. The applied internal fixation method does not standardize mechanical loading over the defect to enable detecting small differences in bone regeneration performances of bone substituting biomaterials. In conclusion, the fixation method requires further optimization to reduce the effects of the operative procedure and make the mechanical loading more consistent and improve the overall sensitivity of this rat femur defect model.
authors.affiliation: Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands. Electronic address: s.aminyavari@tudelft.nl.
authors.forename: S Amin
authors.initials: SA
authors.lastname: Yavari
authors.affiliation: Orthopaedic Research Laboratory, Department of Orthopaedics, Erasmus University Rotterdam Medical Centre, Rotterdam, The Netherlands.
authors.forename: J
authors.initials: J
authors.lastname: van der Stok
authors.affiliation: Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands.
authors.forename: S M
authors.initials: SM
authors.lastname: Ahmadi
authors.affiliation: KU Leuven, Department of Mechanical Engineering, Section Production Engineering, Machine Design and Automation (PMA), Celestijnenlaan 300B, 3001 Leuven, Belgium; LayerWise NV, Grauwmeer 14, 3001 Leuven, Belgium.
authors.forename: R
authors.initials: R
authors.lastname: Wauthle
authors.affiliation: Department of Metallurgy and Materials Engineering, KU Leuven, Kasteelpark Arenberg 44-PB2450, B-3001 Heverlee, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Schrooten
authors.affiliation: Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands; Department of Orthopedics & department of Rheumatology, UMC Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
authors.forename: H
authors.initials: H
authors.lastname: Weinans
authors.affiliation: Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD, Delft, The Netherlands.
authors.forename: A A
authors.initials: AA
authors.lastname: Zadpoor
mesh_terms: D000818:Animals; D001672:Biocompatible Materials; D001860:Bone Plates; D001861:Bone Regeneration; D018786:Bone Substitutes; D055119:Elastic Modulus; D005269:Femur / Q000601:surgery; D020342:Finite Element Analysis; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D016268:Internal Fixators; D007834:Lasers; D008297:Male; D019736:Prostheses and Implants; D051381:Rats; D017208:Rats, Wistar; D014025:Titanium
chemical_list: D001672:Biocompatible Materials; D018786:Bone Substitutes; D014025:Titanium
keywords: Animal models; Implant stiffness; Load transfer; Segmental bone defect model; Variability