title: The mechanical behavior of PMMA/bone specimens extracted from augmented vertebrae: a numerical study of interface properties, PMMA shrinkage and trabecular bone damage.
abstract: Recently published compression tests on PMMA/bone specimens extracted after vertebral bone augmentation indicated that PMMA/bone composites were not reinforced by the trabecular bone at all. In this study, the reasons for this unexpected behavior should be investigated by using non-linear micro-FE models. Six human vertebral bodies were augmented with either standard or low-modulus PMMA cement and scanned with a HR-pQCT system before and after augmentation. Six cylindrical PMMA/bone specimens were extracted from the augmented region, scanned with a micro-CT system and tested in compression. Four different micro-FE models were generated from these images which showed different bone tissue material behavior (with/without damage), interface behavior (perfect bonding, frictionless contact) and PMMA shrinkage due to polymerization. The non-linear stress-strain curves were compared between the different micro-FE models as well as to the compression tests of the PMMA/bone specimens. Micro-FE models with contact between bone and cement were 20% more compliant compared to those with perfect bonding. PMMA shrinkage damaged the trabecular bone already before mechanical loading, which further reduced the initial stiffness by 24%. Progressing bone damage during compression dominated the non-linear part of the stress-strain curves. The micro-FE models including bone damage and PMMA shrinkage were in good agreement with the compression tests. The results were similar with both cements. In conclusion, the PMMA/bone interface properties as well as the initial bone damage due to PMMA polymerization shrinkage clearly affected the stress-strain behavior of the composite and explained why trabecular bone did not contribute to the stiffness and strength of augmented bone.
authors.affiliation: Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Vienna, Austria. kinzl@ilsb.tuwien.ac.at
authors.forename: M
authors.initials: M
authors.lastname: Kinzl
authors.forename: A
authors.initials: A
authors.lastname: Boger
authors.forename: P K
authors.initials: PK
authors.lastname: Zysset
authors.forename: D H
authors.initials: DH
authors.lastname: Pahr
mesh_terms: D000268:Adhesiveness; D000368:Aged; D000369:Aged, 80 and over; D001843:Bone Cements / Q000737:chemistry*; D055119:Elastic Modulus; D005260:Female; D006244:Hardness; D006801:Humans; D008297:Male; D008422:Materials Testing; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D013904:Thoracic Vertebrae / Q000737:chemistry* / Q000502:physiology*; D054854:Vertebroplasty
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate