title: Biomechanical Analysis of a Novel Pedicle Screw Anchor Designed for the Osteoporotic Population.
abstract: OBJECTIVE
  The biomechanical study was performed to investigate the effect of a novel pedicle screw anchor in increasing the pullout strength of pedicle screws.
  
  
  METHODS
  Ten lumbar vertebral bodies with a weighted average T-score of -2.13 were used. Pedicle screws of 4.5 mm diameter and 25 mm length were inserted in to one pedicle randomly and matched with an anchor in the corresponding pedicle. Fatigue testing was performed by applying an axial load of ±200N to the screw tulip, along the axis of the rod, at a rate of 0.5 Hz for 1,000 cycles. After fatigue loading was completed, all screws underwent axial pullout testing at a rate of 0.1 mm/sec until failure. A paired two sample for means t-test was performed to determine a significant difference between the two groups (p ≤ 0.05).
  
  
  RESULTS
  Following fatigue testing, the axial displacement at the 1,000 cycle point for the anchor and non-anchor group was 1.4 ± 0.7mm and 2.9 ± 1.2mm, respectively. The anchor group had significantly lower axial displacement compared to the non-anchor group (p ≤ 0.01). The group with the anchor reached an average maximum load of 702 ± 373N. The average yield load for the non-anchor group was 421 ± 293N. The anchor group yield load was significantly greater than the non-anchor group (p ≤ 0.01).
  
  
  CONCLUSIONS
  A novel anchor for standard pedicle screws resulted in significantly less axial movement during fatigue and a greater failure force compared a screw with no anchor. The anchor may provide a stronger bone-to-screw interface, than a non-anchor screw, without the complications of cement augmentation.
authors.affiliation: Stanford Medical Center, Stanford, California, USA; Central Michigan University Program of Neuroscience, Mount Pleasant, Michigan, USA.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Gates
authors.affiliation: Globus Medical Inc., Audubon, Pennsylvania, USA. Electronic address: mmoldavsky@globusmedical.com.
authors.forename: Mark
authors.initials: M
authors.lastname: Moldavsky
authors.affiliation: Globus Medical Inc., Audubon, Pennsylvania, USA.
authors.forename: Kanaan
authors.initials: K
authors.lastname: Salloum
authors.affiliation: Central Michigan University Program of Neuroscience, Mount Pleasant, Michigan, USA.
authors.forename: Gary L
authors.initials: GL
authors.lastname: Dunbar
authors.affiliation: Stanford Medical Center, Stanford, California, USA.
authors.forename: Jon
authors.initials: J
authors.lastname: Park
authors.affiliation: Globus Medical Inc., Audubon, Pennsylvania, USA.
authors.forename: Brandon
authors.initials: B
authors.lastname: Bucklen
mesh_terms: D000368:Aged; D001577:Benzophenones; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D001843:Bone Cements; D004867:Equipment Design; D004868:Equipment Failure; D005260:Female; D006801:Humans; D007659:Ketones; D008297:Male; D008875:Middle Aged; D010024:Osteoporosis / Q000473:pathology / Q000601:surgery*; D065289:Pedicle Screws; D011092:Polyethylene Glycols; D011108:Polymers; D013131:Spine / Q000473:pathology / Q000601:surgery; D053441:Suture Anchors
chemical_list: D001577:Benzophenones; D001672:Biocompatible Materials; D001843:Bone Cements; D007659:Ketones; D011108:Polymers; C063834:polyetheretherketone; D011092:Polyethylene Glycols
keywords: Anchor; Osteoporosis; Pedicle screw pullout