title: A finite element model of the L4-L5 spinal motion segment: biomechanical compatibility of an interspinous device.
abstract: The biomechanical compatibility of an interspinous device, used for the "dynamic stabilization" of a diseased spinal motion segment, was investigated. The behaviour of an implant made of titanium based alloy (Ti6Al4V) and that of an implant made of a super-elastic alloy (Ni-Ti) have been compared. The assessment of the biomechanical compatibility was achieved by means of the finite element method, in which suitable constitutive laws have been adopted for the annulus fibrosus and for the metal alloys. The model was aimed at simulating the healthy, the nucleotomized and the treated L4-L5 lumbar segment, subjected to compressive force and flexion-extension as well as lateral flexion moments. The computational model has shown that both the implants were able to achieve their main design purpose, which is to diminish the forces acting on the apophyseal joints. Nevertheless, the Ni-Ti implant has shown a more physiological flexural stiffness with respect to the Ti6Al4V implant, which exhibited an excessive stiffness and permanent strains (plastic strains), even under physiological loads. The computational models presented in this paper seems to be a promising tool able to predict the effectiveness of a biomedical device and to select the materials to be used for the implant manufacturing, within an engineering approach to the clinical problem of the spinal diseases.
authors.affiliation: Laboratory of Biological Structure Mechanics, Department of Structural Engineering, Politecnico di Milano, 32-20133 Milano, Italy. vena@stru.polimi.it
authors.forename: Pasquale
authors.initials: P
authors.lastname: Vena
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Franzoso
authors.forename: Dario
authors.initials: D
authors.lastname: Gastaldi
authors.forename: Roberto
authors.initials: R
authors.lastname: Contro
authors.forename: Villiam
authors.initials: V
authors.lastname: Dallolio
mesh_terms: D000497:Alloys; D003198:Computer Simulation; D019544:Equipment Failure Analysis / Q000379:methods; D020342:Finite Element Analysis; D006801:Humans; D007405:Intervertebral Disc Displacement / Q000503:physiopathology* / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D008297:Male; D008422:Materials Testing / Q000379:methods; D008954:Models, Biological; D009068:Movement; D009532:Nickel; D011379:Prognosis; D019736:Prostheses and Implants; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: D000497:Alloys; C040654:titanium nickelide; C031462:titanium alloy (TiAl6V4); D009532:Nickel; D014025:Titanium