title: Biomechanical analysis of different types of pedicle screw augmentation: a cadaveric and synthetic bone sample study of instrumented vertebral specimens.
abstract: This study aims to determine the pull-out strength, stiffness and failure pull-out energy of cement-augmented, cannulated-fenestrated pedicle screws in an osteoporotic cadaveric thoracolumbar model, and to determine, using synthetic bone samples, the extraction torques of screws pre-filled with cement and those with cement injected through perforations. Radiographs and bone mineral density measurements from 32 fresh thoracolumbar vertebrae were used to define specimen quality. Axial pull-out strength of screws was determined through mechanical testing. Mechanical pull-out strength, stiffness and energy-to-failure ratio were recorded for cement-augmented and non-cement-augmented screws. Synthetic bone simulating a human spinal bone with severe osteoporosis was used to measure the maximum extraction torque. The pull-out strength and stiffness-to-failure ratio of cement pre-filled and cement-injected screws were significantly higher than the non-cement-augmented control group. However, the cement pre-filled and cement-injected groups did not differ significantly across these values (p=0.07). The cement pre-filled group had the highest failure pull-out energy, approximately 2.8 times greater than that of the cement-injected (p<0.001), and approximately 11.5 times greater than that of the control groups (p<0.001). In the axial pull-out test, the cement-injected group had a greater maximum extraction torque than the cement pre-filled group, but was statistically insignificant (p=0.17). The initial fixation strength of cannulated screws pre-filled with cement is similar to that of cannulated screws injected with cement through perforations. This comparable strength, along with the heightened pull-out energy and reduced extraction torque, indicates that pedicle screws pre-filled with cement are superior for bone fixation over pedicle screws injected with cement.
authors.affiliation: Orthopaedics Department, Tri-Service General Hospital, Taipei, Taiwan; National Defense Medical Center, Taipei, Taiwan.
authors.forename: Kuo-Hua
authors.initials: KH
authors.lastname: Chao
authors.forename: Yu-Shu
authors.initials: YS
authors.lastname: Lai
authors.forename: Wen-Chuan
authors.initials: WC
authors.lastname: Chen
authors.forename: Chia-Ming
authors.initials: CM
authors.lastname: Chang
authors.forename: Colin J
authors.initials: CJ
authors.lastname: McClean
authors.forename: Chang-Yuan
authors.initials: CY
authors.lastname: Fan
authors.forename: Chia-Hao
authors.initials: CH
authors.lastname: Chang
authors.forename: Leou-Chyr
authors.initials: LC
authors.lastname: Lin
authors.forename: Cheng-Kung
authors.initials: CK
authors.lastname: Cheng
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001843:Bone Cements; D001863:Bone Screws; D002102:Cadaver; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D008875:Middle Aged; D019637:Orthopedic Procedures / Q000295:instrumentation*; D010024:Osteoporosis / Q000601:surgery; D013131:Spine; D019415:Torque
chemical_list: D001843:Bone Cements
keywords: Bone screw; Dimensions; Insertion; Performance requirements; Pull-out; Static; Test methods; Torsion