Abstract
Background
The overall incidence of neurological symptoms attributed to lumbar misplaced screws has been described to occur in 3.48% of patients undergoing surgery. These lumbar radicular neurological lesions are undetected with conventional intraoperative neurophysiological and radiological controls. The hypothesis of this study was that direct stimulation of the pedicle screw after placement in the lumbar spine may not work as well as for screws placed in the thoracic pedicles. A more suitable method for the lumbar spine could be the stimulation of the pedicle track with a ball-tipped probe.
Methods
Comparative observational study on the detection of malpostioned lumbar pedicle screws using two different techniques in two different periods: t-EMG screw stimulation (2011–2012) and track stimulation (2013–2014). A total of 1440 lumbar pedicle screws were placed in 242 patients undergoing surgery for vertebral deformities in the last four years (2011–2014). In the first two years, 802 lumbar screws were neuromonitored using t-EMG during. In the last two years, 638 screws were placed after probe stimulation of the pedicle track. Standardised t-EMG conventional registration and fluoroscopy were afterwards performed in all cases.
Results
Six patients (4.4%) in the t-EMG group without signs of screw misplacement developed radicular pain. After checking with CT scan, a caudal prominence of the screw at the inferior aspect of the pedicle was detected in 7 screws (0.9%) and they were removed. After removal, probe stimulation was performed at the middle track showing abnormal thresholds (3.9–9.7mA). In the second group (track stimulation), 11 cases (10.8%) had thresholds below 7 mA. In these cases, the intrapedicular route was changed. None of these 106 patients presented postoperative radiculopathy and CT scans showed that all screws were well positioned.
Conclusions
The t-EMG stimulation of lumbar pedicle screws offer some false negatives cases. However, the record in the middle pedicle track is able to detect misplaced screws and prevent the development of lumbar radiculopathy. Therefore, systematic pedicle track stimulation is strongly recommended in the lumbar spine.
Level of Evidence
Level III
