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Can Triggered Electromyography Be Used to Evaluate Pedicle Screw Placement in Hydroxyapatite-Coated Screws: An Electrical Examination

Davis, Timothy T.*; Tadlock, Stephanie; Bernbeck, Johannes; Fung, Daniel A.*; Molinares, Diana M.

Journal of Clinical Neurophysiology: April 2014 - Volume 31 - Issue 2 - p 138–142
doi: 10.1097/WNP.0000000000000040
Original Research
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Objectives: 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.

*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.

Address correspondence and reprint requests to Daniel A. Fung, MD, Orthopedic Pain Specialists, 2811 Wilshire Boulevard, Suite 850, Santa Monica, CA, 90403; e-mail: dfung@orthopaindocs.com.

© 2014 by the American Clinical Neurophysiology Society