Repair of the pars interarticularis defect with a cable-screw construct. A preliminary report.

Abstract

To report on the preliminary results of preparing and reconstructing the pars interarticularis with a cable-screw construct. The success of previous techniques to repair the pars defect has been variable. To assess the results of a new technique for stabilizing the pars interarticularis, using the strongest materials, pedicle screws, and cables in the strongest bony elements--the pedicle and lamina. Previous techniques have been inadequate structurally to stabilize the pars interarticularis effectively, or the techniques were difficult to perform. Placing a screw across the defect was technically difficult and took away from the surface area of the fusion. The Scott technique used wiring between the transverse process and spinous process; and in the Morscher Technique, a hook screw was used to repair the pars defect--a technically difficult procedure, using bulky hardware. Patients with pars interarticularis defects were carefully selected for this technique if they had primarily low back pain that did not respond to conservative treatment. The eligible patient had Grade I or less spondylolisthesis, little or no desiccation detectable on magnetic resonance imaging, and pain reproduced with injection of the pars defect. Surgical technique involved placing a special pedicle cable-screw into the pedicle of the involved vertebra. A double cable was passed underneath the lamina, threaded through the hole of the pedicle screw, and wrapped around the spinous process. The cables were simultaneously tensioned and crimped. A tricortical bone graft was compressed between the pedicle and lamina. Seven patients had this technique with a follow-up of 25.5 months (range, 19-37 months). The mean age was 20.5 years (range, 12-32 years), and the mean duration of symptoms was 31 months. All patients had severe pain before surgery that prevented participation in sports and normal daily activities. After surgery, results in five were rated as excellent and in two as good, according to the Prolo score. There were no failures of the cable-screw constructs, and all of the defects appear to have united solidly. The cable-screw construct uses the strongest anchors (the pedicle and the lamina) and uses compression obtained with cables to stabilize the pars interarticularis. Early results indicate that this is a safe and effective technique for this difficult problem.