title: Balancing rigidity and safety of pedicle screw fixation via a novel expansion mechanism in a severely osteoporotic model.
abstract: Many successful attempts to increase pullout strength of pedicle screws in osteoporotic bone have been accompanied with an increased risk of catastrophic damage to the patient. To avoid this, a single-armed expansive pedicle screw was designed to increase fixation strength while controlling postfailure damage away from the nerves surrounding the pedicle. The screw was then subsequently tested in two severely osteoporotic models: one representing trabecular bone (with and without the presence of polymethylmethacrylate) and the other representing a combination of trabecular and cortical bone. Maximum pullout strength, stiffness, energy to failure, energy to removal, and size of the resulting block damage were statistically compared among conditions. While expandable pedicle screws produced maximum pullout forces less than or comparable to standard screws, they required a higher amount of energy to be fully removed from both models. Furthermore, damage to the cortical layer in the composite test blocks was smaller in all measured directions for tests involving expandable pedicle screws than those involving standard pedicle screws. This indicates that while initial fixation may not differ in the presence of cortical bone, the expandable pedicle screw offers an increased level of postfailure stability and safety to patients awaiting revision surgery.
authors.affiliation: Department of Chemical & Biomedical Engineering, University of South Florida, Tampa, FL 33620, USA ; H. Lee Moffitt Cancer Center & Research Institute, Neurooncology Department, Tampa, FL 33612, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Shea
authors.affiliation: Department of Chemical & Biomedical Engineering, University of South Florida, Tampa, FL 33620, USA ; H. Lee Moffitt Cancer Center & Research Institute, Neurooncology Department, Tampa, FL 33612, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Doulgeris
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, Neurooncology Department, Tampa, FL 33612, USA.
authors.forename: Sabrina A
authors.initials: SA
authors.lastname: Gonzalez-Blohm
authors.affiliation: Department of Chemical & Biomedical Engineering, University of South Florida, Tampa, FL 33620, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Lee
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, Neurooncology Department, Tampa, FL 33612, USA ; Departments of Neurosurgery and Orthopedics, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
authors.forename: Kamran
authors.identifier: 0000-0002-5085-8115
authors.initials: K
authors.lastname: Aghayev
authors.affiliation: H. Lee Moffitt Cancer Center & Research Institute, Neurooncology Department, Tampa, FL 33612, USA ; Departments of Neurosurgery and Orthopedics, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
authors.forename: Frank D
authors.initials: FD
authors.lastname: Vrionis
mesh_terms: D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D008422:Materials Testing; D010024:Osteoporosis / Q000503:physiopathology / Q000601:surgery*; D065289:Pedicle Screws; D019904:Polymethyl Methacrylate / Q000737:chemistry
chemical_list: D019904:Polymethyl Methacrylate