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Intraoperative electromyography monitoring in minimally invasive transforaminal lumbar interbody fusion

Rajesh K. Bindal and Subrata Ghosh

Object

Minimally invasive transforaminal lumbar interbody fusion (TLIF) is an increasingly popular method for achieving lumbar decompression and fusion. The procedure is technically more demanding than open fusion, with correspondingly more theoretical risk of complication. The authors describe the use of intraoperative electromyography (EMG) as an adjunct to surgery to reduce the risk of complications.

Methods

Between August 2005 and April 2006, 25 consecutive patients underwent minimally invasive TLIF in which a total of 105 pedicle screws were placed. Intraoperative EMG was performed and included passive recordings during decompression and interbody graft placement, as well as active recording during the placement of the pedicle access needle and testing of the pedicle tap. A uniform protocol for active monitoring was used, with the pedicle access needle set at 7 mA. To assess hardware placement, all patients underwent postoperative radiography and 20 underwent postoperative computed tomography (CT) scanning.

In no patient did the authors observe significant EMG activation during decompression. In five cases, intermittent nerve root firing was noted after the interbody graft was placed, but this did not correlate with any postoperative deficits. Using the active stimulation protocol, 76.2% of screw placements required one or more changes to the trajectory of the pedicle access needle. With successful placement of the pedicle access needle, in all 105 screws, the pedicle tap nerve root stimulation threshold was greater than 15 mA. Postoperative radiography was performed in all patients and CT scanning was performed in 20 patients (with 85 screws being placed). Postoperative imaging revealed only three cases of pedicle breach. In all cases, the breach was at the lateral wall of the pedicle and not thought to be clinically relevant.

Conclusions

A continuous stimulation pedicle access needle alerts the surgeon to incorrect medial trajectories and may lead to safer pedicle cannulation. As a result of electrophysiological feedback, the pedicle access needle trajectory was altered in 76.2% of the reported cases. The use of the authors’ protocol resulted in a 0% incidence of clinically relevant malpositioned hardware and a low overall neurological complication rate. Intraoperative nerve root monitoring is a useful adjunct to minimally invasive TLIF.

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Surgeon and patient radiation exposure in minimally invasive transforaminal lumbar interbody fusion

Clinical article

Rajesh K. Bindal, Sharon Glaze, Meghann Ognoskie, Van Tunner, Robert Malone, and Subrata Ghosh

Object

Minimally invasive transforaminal lumbar interbody fusion (TLIF) is an increasingly popular procedure. The technique involves use of fluoroscopy to assist with pedicle screw (PS) placement. The potential exists for both the surgeon and the patient to become exposed to significant amounts of radiation. The authors undertook this study to quantify the radiation dose to the surgeon and patient during minimally invasive TLIF.

Methods

The authors undertook a prospective study of 24 consecutive patients who underwent minimally invasive TLIF. All surgeries were performed by the senior author (R.K.B.), who used techniques previously described. The surgeon wore a radiation monitor under an apron-style lead shield at waist level, at an unshielded collar location, and as a sterile ring badge containing a thermoluminescent dosimeter on the dominant (right) hand ring finger. Dosimeter readings were obtained for each case. A total of 33 spinal levels were treated in 24 patients. All treated levels were between L3–4 and L5–S1. In all cases of 1-level disease, 4 PSs were placed, and in all cases of 2-level disease, 6 screws were placed.

Results

. Mean fluoroscopy time was 1.69 minutes per case (range 3.73–0.82 minutes). Mean exposure per case to the surgeon on his dominant hand was 76 mRem, at the waist under a lead apron was 27 mRem, and at an unprotected thyroid level was 32 mRem. Mean exposure to the patient's skin was 59.5 mGy (range 8.3–252 mGy) in the posteroanterior plane and 78.8 mGy (range 6.3–269.5 mGy) in the lateral plane.

Conclusions

To the authors' knowledge, this is the first study of radiation exposure to the surgeon or patient in minimally invasive TLIF. Patient exposures were low and compare favorably with exposures involving other common interventional fluoroscopically guided procedures. Surgeon exposures are limited but require careful monitoring. Annual dose limits could be exceeded if a large number of these and other fluoroscopically guided procedures were performed.