Outcome-based classification for assessment of thoracic pedicular screw placement

Study Design. Prospective cohort study. Objective. We propose a simple outcome-based classification for assessment of pedicle screw positions based on postoperative computed tomography scan. This bridges the gap between high rates of pedicle screw misplacement and minimal complications reported. Summary of Background Data. The main deterrent for the use of thoracic pedicular screws is the feared neurovascular complications due to screw misplacements. The literature shows that only a small fraction of the misplaced screws actually causes any complication, and some misplacements can be acceptable both in terms of safety and their biomechanical strength. Methods. Sixty patients with various spinal disorders were included in the study. The mean age was 29.6 years (range, 12-72 years). The patients were divided into 2 groups for assessment of pedicle screw placements using postoperative computed tomography scans: scoliosis group with 24 patients and the nonscoliosis group with 34 patients. Placements of screws were assessed using the outcome-based classification and the Rongming Xu criteria of screw placement. Results. A total of 341 screws were assessed from 60 patients with various spinal disorders (scoliosis and nonscoliosis groups). Using the Rongming Xu criteria, the overall screw misplacement in scoliosis group was 50.72% (68 of 138) and that in nonscoliosis group was 45.45% (80 of 176 screws). Assessment of these screws using the outcome-based classification showed a high percentage of acceptable screw placements (type 1) - 89.85% (124 of 138 screws) in the scoliosis group and 86.93% (153 of 176 screws) in the nonscoliosis group. Conclusion. The literature shows consensus over high rates of pedicle screw misplacement, but low clinical complications, in the hands of the best of spine surgeons. The concept of acceptable screw placements and the outcome classification makes the pedicle screw assessment results correlate better with the clinical outcome.