Lateral mass screw–rod fixation of the cervical spine: a prospective clinical series with 1-year follow-up*1

Abstract

Background context Lateral mass plating has become the technique of choice for posterior cervical fixation. Although these systems are safe and reliable, they can be difficult to use in patients with abnormal cervical anatomy; screw placement can be compromised by the fixed hole spacing of the plate; screw back-out and other forms of implant failure can occur; and extension across the cervicothoracic junction can be problematic. Purpose To report a series of patients undergoing posterior cervical stabilization with a polyaxial screw–rod construct and to investigate whether this new system offers any advantages over existing methods of fixation. Study design A prospective study evaluating clinical and radiographic parameters in a consecutive series of patients treated with this technique. Patient sample There were 21 patients in the study group. The surgical indication was cervical spondylosis in 14, trauma in 2, postsurgical kyphosis in 2 and 1 case each of congenital cervicothoracic stenosis, C7–T1 pseudarthrosis and basilar invagination with brainstem compression. Outcome measures Clinical indicators included age, gender, neurologic status, surgical indication and number of levels stabilized. Note was made of whether laminectomy and concomitant anterior reconstructive surgery were performed. Radiographic indicators included early postoperative computed tomography (CT) scan to check for screw placement and plain radiographs at subsequent visits. Methods The participants in this study underwent posterior cervical stabilization using lateral mass screw–rod fixation. Clinical and radiographic assessment was carried out immediately after surgery, and 3, 6 and 12 months after surgery. One-year follow-up was obtained in all cases. Results A total of 212 screws were implanted in 21 patients. Fixation was carried out over an average of 5.5 spinal segments (range, 2 to 11). The system was successfully implanted in all patients despite the presence of coronal and sagittal plane deformities and/or lateral mass abnormalities in the majority of cases. This system allowed for screw placement in the occiput, C1 lateral mass, C2 pars, C3–C7 lateral masses and upper thoracic pedicles. Early postoperative CT scanning confirmed satisfactory screw placement in all cases. Three patients experienced transient single-level radiculopathy, for an incidence of 1.4% per screw placed. Two patients developed wound seromas requiring evacuation. There were no infections or other wound healing problems. There were no examples of cord or vertebral artery injury, cerebrospinal fluid leak, screw malposition or back-out, loss of alignment or implant failure. When compared with plating techniques, screw–rod fixation appeared to offer several advantages. First, unlike plates, rods proved to be amenable to multiplanar contouring, which is often needed for deformities associated with cervical spondylosis. Second, lateral mass screw placement was more precise because it was not constrained by the hole spacing of the plate. Third, screw back-out and other types of implant failure were not seen. Fourth, the screw–rod system was more easily extended to the occiput and across the cervicothoracic junction. Fifth, the screw–rod system permitted the application of compression, distraction and reduction forces within the construct, to a greater extent than plate systems. The incidence of postoperative radiculopathy was similar to that seen with plate systems. Conclusions These data indicate that posterior cervical stabilization with polyaxial screw–rod fixation is a safe, straightforward technique that appears to offer some advantages over existing methods of fixation. Results appear to be durable at 1-year follow-up. Benefits are more significant with longer constructs, especially those extending to the occiput or crossing the cervicothoracic junction.