Intraosseous Ultrasound in the Placement of Pedicle Screws in the Lumbar Spine

Study Design. Experimental and intraoperative evaluation of the efficiency of a novel technique. Objective. To determine the accuracy of pedicle screw hole placements before screw implantation in the lumbar spine. Summary of Background Data. Deviations from planned trajectories occur in a significant number of screw placements in posterior lumbar fixation. Several techniques have been proposed to minimize this complication, although none has gained general acceptance. This may be due to costs associated with their implementation or considerably extended operating times required by some techniques. Methods. Pedicle screw holes were placed in 24 pedicles of 2 postmortem human lumbar spine specimens. Sixteen optimal trajectories were placed and 8 intentional cortical breaches. Each pedicular drill hole was examined using a 360 ultrasound transducer and CT scanning. The ultrasonographic images were reviewed by 3 independent investigators who were blinded to the CT findings. In addition, 20 screw holes were placed intraoperatively in 3 patients, and equally assessed by intraoperative intraosseous ultrasonography and postoperative CT scanning. Results. Ultrasonographic images of pedicle screw holes in postmortem human spine specimen were correctly interpreted in 99% of cases. No cortical breech was missed, i.e., no false-negatives occurred. Intraoperative findings closely matched the experimental data. None of the intraoperative ultrasound scans demonstrated a cortical breach, a finding confirmed by postoperative CT. The intraoperative time required for the ultrasonographic analysis of each pedicle was about 1 minute and the interpretation of the resulting images was judged intuitive by the evaluating neurosurgeons. Conclusion. Intraosseous ultrasound is a highly reliable technique for the intraoperative assessment of pedicle screw holes before pedicle screw placement. Additional expenses with respect to procedure time and manpower are minimal.