Retrospective clinical study. To assess the accuracy of multilevel registration for skip pedicle screw placement during image-guided, computer-assisted spine surgery, in the setting of adolescent idiopathic scoliosis (AIS). Computerized frameless stereotactic image-guidance has been used recently to improve pedicle screw placement accurately and safety during spine surgery. Because of possible intervertebral motion and usual difference in patients' position between preoperative imaging and surgery, the imaging model and the surgically exposed spine may be significantly discordant. Consequently, current protocols suggested separate registration of each spinal level (single-level registration) before respective pedicle screw placement, a time-consuming process. Moreover, although multilevel registration for lumbar spine has been reported, and that for thoracic spine has not. A total of 19 patients (1 male and 18 females; mean age, 13.9 years) with AIS who underwent multilevel registration for skip pedicle screw placement were included. Variables including surgical time, blood loss, preoperative and 2-year postoperative Cobb angle, correction rate, and postoperative screw position by computed tomography image were evaluated. Mean registration error after point merge and again after surface merge were recorded for each consecutive vertebra of each case. Mean surgical time was 310 minutes (range, 168–420 min). Mean blood loss 1138 g (range, 300–2300 g). Cobb angle before operation and at 2 years postoperation was 62.4° (43°–100°) and 21.6° (9°–42°), respectively. Mean correction rate 66.2% (39.7%–84.5%). Total 265 screws were inserted with computed tomography-based navigation system. Pedicle violation was observed in only 4 screws (1.5%). No neurovascular complication occurred. After point merge, average Mean registration error of all cases was 1.69 ± 0.52 mm, and after surface merge was 0.51 ± 0.16 mm. Multilevel registration may decrease operative time without compromising accuracy of pedicle screw placement afforded by this technique in the setting of AIS.

Uehara M, et al. Asian Spine J. 2014 Dec;8(6):768-776. http://dx.doi.org/10.4184/asj.2014.8.6.768

A retrospective study. To evaluate the surgical results of computer-assisted C1-C2 transarticular screw fixation for atlantoaxial instability and the usefulness of the navigation system. We used a computed tomography (CT)-based computer navigation system in planning and screw insertion in Magerl's procedure, which provides the most rigid atlantoaxial fusion, to avoid risk of vertebral artery (VA) tear by avoiding high-riding VA during screw insertion. Twenty patients who underwent atlantoaxial fusion under the CT-based navigation system were studied. The mean observation period was 33.5 months. The evaluated items included the existence of VA stenosis by preoperative magnetic resonance angiography, surgical time, blood loss volume, Japanese Orthopaedic Association (JOA) score and Ranawat's pain criteria before surgery and at final follow-up, postoperative screw position evaluated by CT, and bony fusion. The mean operation time was 205 minutes, with the mean blood loss volume of 242 ml. The mean JOA score was 11.6 points before surgery and 13.7 at final follow-up. Occipital and/or cervical pain presented before operation was remitted or resolved in all patients. Evaluation of screw insertion by CT revealed correct penetration to atlantoaxial joints, with a perforation rate of 2.6%. There was no complication, including VA tear, and all patients who were followed-up during one year or more after surgery achieved bony fusion. Some subjects who appeared inappropriate for surgery from CT images were assessed as eligible for surgery based on the evaluation results obtained using the navigation system. It was demonstrated that the CT-based navigation system is an effective support device for Magerl's procedure.