EMG Monitoring During Minimally Invasive Fusion of the SI Joint

Electromyography in the Operating Room

EMG nerve monitoring in lumbar surgery makes up a large percentage of cases monitored every year. Using EMG nerve monitoring during SI joint fusions seems to be less utilized, even though the option is available to surgeons using nerve monitoring for their lumbar cases.

EMG from a surgical neurophysiologist perspective is a love/hate relationship. It can give useful information in certain cases, like during suboccipital craniotomies, pedicle screw stimulation, and thyroidectomies, but is more art than science on cases like monitoring the RLN during ACDF cases.

So when we look to expand the use of monitoring modalities to different case types, we need to answer the questions "can we" and "should we."

One such instance is SI Joint surgery.

Using EMG Nerve Monitoring for Minimally Invasive Fusion of the Sacroiliac Joint

Knowing the difficulty of identifying sacral foramen on imaging and the variations seen in sacral bones, it made me wonder why nerve monitoring would not be used more often. It seems that it could be as useful, or even more useful, during the searching phase when placing the implant than even than just stimulating the final position. If the surgeon’s visual guidance is reliant on less than optimal conditions, adding in this physiological test should allow for the surgeon to make a more informed decision.

So I went hunting for an article in hopes to find something useful and came across the following article from Woods et al.

Woods, M., Birkholz, D., MacBarb, R., Capobianco, R., and Woods, A. (2014). Utility of Intraoperative Neuromonitoring during Minimally Invasive Fusion of the Sacroiliac Joint. Advances in Orthopedics, 2014, pp.1-7.

Their Findings

Right off the bat… yes, this is a small, retrospective study. But I do like how they are using nerve monitoring through different stages of the implantation process. The intensities used were created by looking at animal studies and stimulation intensities used for EMG nerve monitoring in lumbar surgeries, but are probably best guesses and seemed reasonable to me at this point in time.

In their findings, they stated “111 implants resulted in 8 true positives, 3 false positives, 2 false negatives, and 98 true negatives. These results provide sensitivity and specificity rates of 80% and 97%, respectively.”

But if you look at the descriptions of the false negatives and false positives, there are lessons to be learned there. For the false negatives, the first case demonstrates the usefulness of EMG nerve monitoring in a “searching” mode to better identify problems. The second case is questionable to point to the EMG nerve monitoring as the problem. For the 3 false positives found in the single patient, the limitation of EMG nerve monitoring in that patient was very real. As it turns out, there seemed to be an anatomical variant

For the 3 false positives found in the single patient, the limitation of EMG nerve monitoring in that patient was very real. As it turns out, there seemed to be an anatomical variant causing a problem in the sensitivity of the modality. Knowing that this surgery is in an area where anatomical variations are not uncommon, the surgical neurophysiologist and surgeon would be able to make a better judgment of the recordings as it relates to their other measures (fluoroscopy, experience, etc) and tilt towards a greater reliance on those in cases where there is a known variation that might cause a challenge to EMG nerve monitoring (like dysplasia).

While I wish the author would have gone into a little more detail on the false-negative cases, and I really wish they were able to include a larger patient population, the paper did give some guide to utilizing EMG nerve monitoring for minimally invasive sacral iliac surgery that I hope will spark further study and implementation.

Minimally Invasive Surgery Video

For those less familiar with the surgical procedure, here’s a video of one type of minimally invasive system to fuse the sacroiliac joint:

To learn more about IONM, visit www.IntraoperativeNeuromonitoring.com.