Cortical screw fixation using CT-navigation coupled with real-time electrophysiological monitoring of individual screw placement for unstable degenerative lumbar spondylolisthesis

Introduction: Cortical screws offer a less invasive alternative compared to traditional pedicle screws. These screws are inserted in an inferomedial to superolateral trajectory achieving greater cortical bone purchase. Similar fusion rates, pain relief, and decreased surgical morbidity at 12-month follow-up have been documented when compared to traditional pedicle screws. Using intra-operative imaging, neuronavigation, and individual neurophysiological monitoring of each screw, we showed that this is a safe surgical approach. Methods: Institutional review board (IRB) approved retrospective review of medical records for 173 patients to determine eligibility. Cases had to be elective one-or two-level fusion with surgical indication. Functional improvement was measured with Oswestry Disability Index (ODI) at pre and post-operative visits. Surgical morbidity data, individual screw thresholds, and radiographic evidence of stability was collected from electronic medical records (EMR). Results: A total of 153 patients met criteria with mean age 66.60 +/- 9.30 (range: 34-84) and mean BMI of 28.76 +/- 4.47 kg/m(2). Of 558 screws inserted, no screws recorded <8 mA upon stimulation, thus no screw required repositioning. There were no pedicle or central canal breach related to screw insertion. ODI decreased from 44.83 +/- 18.02 to 19.46 +/- 19.52 at 3-months post-operative (p < 0.0001). A subset of 30 patients had 12-month post ODI, which showed a change from 41.22 +/- 18.42 to 22.63 +/- 22.01 at 12-months (p < 0.001). Conclusions: Within, we discuss our approach for inserting cortical screws in posterior lumbar fusion for patients with unstable degenerative lumbar spondylolisthesis. Our study shows that the implementation of intraoperative imaging, neuronavigation, and neurophysiological monitoring of individual screws can provide a safe environment for cortical screw insertion. This approach allows for a less invasive approach and greater quality bone purchase while mitigating the associated risks.