Electroretinogram by Donnell J Creel

Figure Reference: Med.Utah.edu (linked, pl click)

In general, intraopertive neurophysiological monitoring teams do not conduct ERG or EOG in the Operating room set up, it is rather cumbersome and difficult to get a reliable readings combined with the difficulty of placing the recording electrode and risks that are associated with the procedure.  However, Donnell in its Chapter on"The electroretinogram" presents the latest developments that record the status of retinal function using skin electrodes and he also sheds light on the recent advancement in ERG the multifocal retiongram. Whether you are going to conduct this test or not, if you are interested in all the evoked potentials and the basics, this is an excellent reading material. Enjoy.

 The Electroretinogram: Clinical Applications by Donnell J. Creel

Electrophysiological testing of patients with retinal disease began in clinical departments in the late nineteen forties. Under the influence of the Swedish pioneers, Holmgren (1865) and Granit (1933), the electroretinogram was being dissected into component parts and early intraretinal electrode studies were beginning to tell which cells or cell layers gave rise to the various components. A detailed discussion of the electroretinogram, or ERG as it is commonly abbreviated, is found in the accompanying chapter by Ido Perlman. A little after the introduction of the ERG as a test of the state of the patient’s retina, another diagnostic test called the electrooculogram (EOG) was introduced to the clinic (Arden et al., 1962). The EOG had advantages over the ERG in that electrodes did not touch the surface of the eye. The changes in the standing potential across the eyeball were recorded by skin electrodes during simple eye movements and after exposure to periods of light and dark. Over the years ERG recording techniques have become progressively more sophisticated in the clinical setting. With the advent of perimetry, optical coherence tomography (OCT) and pattern ERG techniques, more precise mapping of dysfunctional areas of the retina is now possible. The most recent advance in ERG technology is the multifocal electroretinogram (mfERG). The mfERG provides a detailed assessment of the health of the central retina.

Pedicle Screws & Triggered EMGs!

Spine (Phila Pa 1976). 2010 Jan 15;35(2):E43-8.

Usefulness of electromyography compared to computed tomography scans in pedicle screw placement.

Duffy MF, Phillips JH, Knapp DR, Herrera-Soto JA.
STUDY DESIGN: This is a retrospective analysis of 30 pediatric deformity surgeries. OBJECTIVE: The purpose of this study was to evaluate the accuracy of neuromonitoring in comparison to postoperative computed tomography scans for pedicle screw position. SUMMARY OF BACKGROUND DATA: Triggered electromyography potentials in aiding the placement of lumbar pedicle screws are considered useful; however, this method is less accepted in thoracic screw placement. METHODS: Thirty pediatric deformity surgeries were reviewed. All screws were placed using fluoroscopic assistance. Electromyography data were obtained on all screws. Every patient underwent postoperative computed tomography scanning. Computed tomography scans were assessed by all authors, and each screw was classified. Sensitivity, specificity, negative predictive value, and likelihood ratios were determined for the cut-off value of an electromyography > or =6 mA. RESULTS: A total of 329 screws were reviewed. No complications occurred. An overall accuracy of 93% was obtained. No retained screw had greater than 2 mm medial pedicle wall breach. Nine screws were removed intraoperatively due to medial breach. The mean electromyography potential for all classes of screws was not statistically different (P > 0.1). The negative predictive value of the test was 0.92 in the thoracic spine and 0.93 in the lumbar spine. The negative likelihood ratios were 0.96 and 0.35 for the thoracic and lumbar spines respectively, and the positive likelihood ratio was 1.4 for the thoracic spine and 12.5 for the lumbar spine. CONCLUSION: Thoracic and lumbar pedicle screws are safe surgical options in the treatment of pediatric scoliosis. Comparison of electromyography potentials and postoperative computed tomography scans showed no statistically significant difference for all classes of screws. The likelihood ratio for electromyography testing was more clinically significant in the lumbar spine. A triggered electromyography value greater than or equal to 6 mA has a high likelihood of that screw being in the "safe zone." However, there is no true electromyography cut-off value that guarantees accurate placement and avoidance of neurologic injury.