title: Can triggered electromyography be used to evaluate pedicle screw placement in hydroxyapatite-coated screws: an electrical examination.
abstract: OBJECTIVE
  To assess if hydroxyapatite (HA)-coated titanium pedicle screws exhibit the same electroconductive characteristics as non-HA-coated screws.
  
  
  METHODS
  Resistance measurements were obtained from a random sampling of 10 HA-coated pedicle screws and 10 non-HA-coated screws, and surgical conditions simulated. Surface resistivity measurements were taken for each screw to determine voltage drop over its entire length.
  
  
  RESULTS
  The non-HA-coated screws tested showed low resistive properties and proved to be an ideal conductor of electrical current. The resistive properties associated with the HA-coated pedicle screws were found to be similar to those of commonly used insulators removing the effectiveness of triggered electromyographic responses.
  
  
  CONCLUSIONS
  Based on test results, these data suggest that the resistance value of the HA-coated screw is large enough to prevent modern Intra-Operative Monitoring (IOM) equipment from delivering the necessary current through the shank of the screw to create a diagnostic electromyographic response. Any response that would be produced would be because of shunting of electric current from the non-coated head of the screw into adjacent tissue and not through the shank of the screw. These study results suggest that HA-coated screws cannot be stimulated to assist in determining the accuracy of pedicle screw placement.
authors.affiliation: *Orthopedic Pain Specialists, Santa Monica, California, U.S.A.; †Alpha Diagnostics, Santa Monica, California, U.S.A.; and ‡Orthopedic Surgery Department, Kaiser Medical Group Los Angeles, California, U.S.A.
authors.forename: Timothy T
authors.initials: TT
authors.lastname: Davis
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tadlock
authors.forename: Johannes
authors.initials: J
authors.lastname: Bernbeck
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fung
authors.forename: Diana M
authors.initials: DM
authors.lastname: Molinares
mesh_terms: D001863:Bone Screws; D017886:Durapatite; D017097:Electric Impedance; D004569:Electroencephalography; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D006801:Humans; D016343:Monitoring, Intraoperative; D013119:Spinal Cord Injuries / Q000601:surgery; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods*; D014025:Titanium
chemical_list: D017886:Durapatite; D014025:Titanium