[Injuries of the lower cervical vertebrae--the monocortical stabilization technique].

PURPOSE OF THE STUDY: In contrast to the thoracolumbal spine, the cervical spine bears a lower biomechanical load and, therefore, anterior stabilization of a fracture is a definitive procedure in the majority of cases. What remains the matter of choice is screw fixation in the body of the vertebra involved. This may be either monocortical or bicortical. In this study, we evaluate a group of patients in whom fractures of the lower cervical spine were treated using the CSLP monocortical system (Synthes).

MATERIAL: We included 68 patients in whom complete radiographic data were available and the surgery was performed more than 6 months earlier. This group comprised 49 men and 19 women with the mean age of 37.6 years and range of 12 to 79 years. In the first stage, all patients were operated on from the anterior approach. In 11 (16.2%) patients with type B or C injury, according to the AO classification, the procedure was completed by dorsal stabilization. The definite indication for surgery was any involvement of nerve structures or open fractures; kyphosis greater than 15 degrees, reduction by more that 50% of the proximal edge of the vertebral body, narrowing of the spinal canal by more than 50%, multiple wedge fractures and disc and ligament injuries associated with instability were considered conditional indications.

METHODS: Any locked dislocation was reduced manually under X-ray guidance in the shortest possible time. Subluxations or fractures of the vertebral body were reduced by positioning the patient's body on the operating table. The standard procedure for subluxation management was distraction of the segment by applying a Caspar's distractor and subsequent microscopic discectomy up to the posterior longitudinal ligament. A tricortical bone graft was collected from the iliac crest. After its implantation, the distractor was released and the segment was fixed by a CSLP system (Synthes) with monocortical screws 14 mm long, usually used in a 2 + 2 configuration. In locked dislocation, in addition, the discission of the posterior longitudinal ligament and inspection of the dural sac were performed, and completed by dorsal stabilization with hook plates or a Cervifix fixator (Synthes) in one procedure under anesthesia. When the body of the vertebra was fractured, either partial or subtotal excision of it was carried out according to the type of fracture or when displaced fragments protruded into the spinal canal. A tricortical graft taken from the iliac crest was larger than in the treatment of subluxation but a plate was applied as in monosegmental fixation. In addition, the graft was fixed with special screws that had a porous surface and holes in the shank. Dorsal stabilization with hook plates or a Cervifix fixator was used for severe instability in type B or C injury.

RESULTS: The normal range of cervical spine motion (flexion, extension, inclination, rotation) was found in 44 patients. Slightly limited movement (75% to 90% normal motion) was in 17 patients and seven were affected more seriously (50% to 75% normal motion). Of the 19 patients with neurological deficit, 13 showed improvement by 1, 2 or 3 grades of Frankel's classification in seven, four and two patients, respectively. The first signs of bone remodeling between the graft and covering plate, usually at the distal graft border, were found in 16 patients at 6 weeks and in the remaining 52 patients at 12 weeks. By 6 months postoperatively, all patients showed complete healing and incorporation of the tricortical graft. The cranial screws broke in one case (1.5%) but this had no effect on the treatment outcome. No complication related to the surgical procedure occurred intraoperatively.

DISCUSSION: The very good results achieved with the use of the CSLP monocortical system in this study (98.5% fusion without broken screws or plates) are in agreement with relevant data reported in the Czech and foreign literature. The principal condition is a careful preparation of both the endplates of vertebral bodies and the graft. After insertion, this should stay in place without any tendency to extrude. If the graft is too long, it imposes an increased load on plates or screws that consequently act ventrally.

CONCLUSION: Our experience and literature data suggest that the CSLP monocortical system is fully capable to stabilize the lower cervical spine after injury, supposing all procedures described above are completed. In more serious trauma and type B or C instability, the additional dorsal instrumented fusion is indicated.