title: Biomechanical analysis of pedicle screw thread differential design in an osteoporotic cadaver model.
abstract: BACKGROUND
  Pedicle screw fixation, the standard surgical care for posterior stabilization in the thoraco-lumbar spine has a high rate of failure in osteoporotic individuals. Screw design factors and insertion techniques have been shown to influence the biomechanical performance of pedicle screws. Our objective was to investigate the biomechanical characteristics of pedicle screw fixation in osteoporotic bone by comparing standard screws with newly designed differential crest thickness dual lead screws.
  
  
  METHODS
  An in-vitro spinal-level paired factorial study design was used to examine thoraco-lumbar spine biomechanical outcomes for differential pedicle screw thread designs. Six cadaveric human spines (T8-L5) were tested for six groups (n=20) consisting of 2 different crest thickness and 3 different insertion techniques. Bone mineral density was assessed and peak insertion torque measured while placing one screw of new design and control on the contralateral side. Screw pullout properties were measured from classical American Society for Testing and Materials protocols.
  
  
  RESULTS
  The screws designed specifically for osteoporotic bone showed significantly larger insertion torque compared with the standard screw design irrespective of insertion technique. Much of the variability in pullout failure and stiffness was explained by bone mineral density. The osteoporotic screws of different crest thickness were statistically similar to each other in all outcome measures.
  
  
  CONCLUSIONS
  Compared with standard pedicle screws, the dual lead osteoporotic-specific pedicle screws demonstrated significantly larger insertion torques and similar pullout properties. Non-significant increased biomechanical strength was observed for thin crest compared to thick crest dual lead pedicle screws indicating their enhanced purchase in osteoporotic bone.
authors.affiliation: Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA.
authors.forename: H
authors.initials: H
authors.lastname: Mehta
authors.forename: E
authors.initials: E
authors.lastname: Santos
authors.forename: C
authors.initials: C
authors.lastname: Ledonio
authors.forename: J
authors.initials: J
authors.lastname: Sembrano
authors.forename: A
authors.initials: A
authors.lastname: Ellingson
authors.forename: P
authors.initials: P
authors.lastname: Pare
authors.forename: B
authors.initials: B
authors.lastname: Murrell
authors.forename: D J
authors.initials: DJ
authors.lastname: Nuckley
mesh_terms: D001863:Bone Screws; D002102:Cadaver; D019245:Compressive Strength; D019544:Equipment Failure Analysis; D017276:Friction; D006244:Hardness; D006801:Humans; D008159:Lumbar Vertebrae / Q000503:physiopathology* / Q000601:surgery*; D010024:Osteoporosis / Q000503:physiopathology* / Q000601:surgery*; D011312:Pressure; D011474:Prosthesis Design; D013123:Spinal Fusion / Q000295:instrumentation; D013904:Thoracic Vertebrae / Q000503:physiopathology* / Q000601:surgery*