Direct repair of a defect in the pars interarticularis was performed with use of bone-grafting and internal fixation with a pedicle screw, rod, and laminar hook in order to achieve a higher prevalence of osseous union than that achieved with commonly used procedures. The configuration of the head of the screw, which is designed to allow it to connect with the rod at the necessary angle, simplified the placement of the rod. The procedure was performed in sixteen patients who had a bilateral defect of the pars interarticularis with or without grade-I or II spondylolisthesis, had had failure of non-operative treatment, and had had temporary relief of pain after the area of the defect in the pars interarticularis had been infiltrated with lidocaine. Concomitant degeneration of a disc was not a criterion for exclusion. The patients were followed for an average of twenty-five months (range, twenty-four to twenty-eight months). The average age at the time of the operation was thirty-two years (range, twelve to sixty years). Six patients had findings of nerve-root compression on myelography with computerized tomographic scanning, and the bone spurs overlying the affected nerve root around the defect in the pars interarticularis were removed with an ultrasonic osteotome through a small window. The implant was removed about one year after the operation. Oblique radiographs showed osseous union in the previous defect bilaterally in all sixteen patients. Thirteen patients were free of symptoms, and three had major improvement with occasional low-back pain. None had a complication, such as infection, breakage of the implant, or irritation of a nerve root.The method used for direct repair of the defect of the pars interarticularis in these patients proved to be simple and effective. Relief of symptoms appeared to depend on decompression of the affected nerve root, if one was involved, and on preoperative prediction of the locus of the symptoms by infiltration of the pars interarticularis with lidocaine.
†Department of Orthopaedic Surgery, Osaka Police Hospital, 10-31 Kitayama-cho, Tennoji-ku, Osaka 543, Japan.