Reduction of lumbar spondylolisthesis using a CDI pedicle screw system.

To evaluate reduction methods using two of the several types of Cotrel-Dubousset instrumentation (CDI), 39 patients with low-grade (Meyerding grades I and II [12]) lumbar spondylolisthesis were followed clinically and radiologically for a minimum of 6 months. Our surgical methods were classified into three types as follow: reduction by 2-level assembly using double-threaded screws (type I); reduction by single-level assembly using the double-threaded screws (type II); and reduction by single-level assembly using tulip screws (type III). We found that satisfactory reduction could be achieved by single-level assembly using either the double-threaded or tulip screw without resection of disc material or the posterior leverage method. We found that the tulip screw was superior in obtaining stable reduction. We discuss the mechanism of reducing spondylolisthesis in comparison with that of previously reported methods.