Prospective Controlled Study of Rectangular Titanium Cage Fusion Compared With Iliac Crest Autograft Fusion in Anterior Cervical Discectomy

Dimitris Zevgaridis, M.D., Claudius Thomé, M.D., Joachim K. Krauss, M.D., Department of Neurosurgery, University Hospital Mannheim, Mannheim, Germany.

Neurosurg Focus. 2002;12(1) 

In This Article

Clinical Material and Methods

Thirty-six patients with symptomatic one-or two-level cervical disc disease (spondylosis and/or herniated cervical disc) refractory to adequate conservative treatment were recruited consecutively for this study. Patients with ossification of the posterior longitudinal ligament, previous cervical disc surgery, and/or spinal instability were excluded. All patients underwent anterior cervical microdiscectomy in which standard techniques were used. In the first 18 patients, iliac crest autograft fusion was performed. In the next 18 patients, RABEA RTCs (RABEA; Signus, Alzenau, Germany) were inserted in the intervertebral disc space.

The demographic and clinical data were comparable between groups. Mean age at surgery was 51 years in the iliac crest autograft group and 52 years in the RTC group. The mean duration of preoperative symptoms was 15 and 13.5 months, respectively. The sex ratio, the pattern of clinical presentation (radiculopathy compared with myelopathy), and the number of treated levels were similar in both groups (Table 1).

Surgical procedures were performed using the common Smith-Robinson anterolateral approach via a right-sided skin incision. The posterior longitudinal ligament was excised thoroughly to ensure adequate neural decompression. Gentle decortication of the endplates was performed using a curette. In the iliac crest autograft group, a tricortical iliac crest graft was then harvested using a standard osteotome technique. The tricortical graft was adjusted to fit into the slightly distracted disc space and countersunk into position.

In the RTC group, the size and shape of the cage was selected based on both the preoperative imaging studies and the intraoperative measurements. The cages were not filled with bone or other material.

The RABEA cage has a cuboid form, is hollow, and has fenestrated surfaces on all sides. The upper and lower surfaces have 1-mm toothed spikes that assist in the positive anchorage of the implant between the VBs. It is produced from forged titanium alloy, which is magnetic resonance imaging compatible. Many size variations are available (Fig. 1).

Photograph showing the RABEA cage equipment. Although the smooth test cages (blue color, at right) are used to fit the properly sized cage into the disc interspace, the implant cages (at left) are characterized by spikes for anchorage into the endplates. Two exemplary sizes and the implant holder are depicted.

Postoperatively, all patients wore a hard cervical orthosis for 6 weeks.

Functional outcome was assessed according to Odom criteria.[28] Outcome was defined as excellent in patients without complaints referable to cervical disc disease and who were able to perform their daily routines without impairment; good outcome was defined as intermittent discomfort related to cervical disc disease that did not significantly interfere with work; satisfactory outcome was defined as subjective improvement but limited physical activities; and poor outcome was defined as an absence of improvement or worsened condition compared with preoperative status.

To evaluate satisfaction with the postoperative result, the PSI was applied.[14,30] The PSI is a modified subitem of the North American Spine Society outcome questionnaire. It is scored as follows: 1) "Surgery met my expectations"; 2) "I did not improve as much as I had hoped but I would undergo the same operation for the same results"; 3) "Surgery helped but I would not undergo the same operation for the same results"; and 4) "I am the same or worse as compared to before surgery." In clinical outcome the improvement of sensory and motor radiculopathy, as well as myelopathy, were evaluated. Pain was assessed by a VAS, as described in detail by Scott and Huskisson.[36] Changes in patients with myelopathy were rated according to the Nurick classification of disability in spondylotic myelopathy.[27]

Radiological evaluation included criteria for fusion and the position of the implant. Standard radiographs were assessed for lucencies in the immediate vicinity of the implants. It was not possible to determine the growth of bone through the cage on the radiographs. Stability was assessed using an overlay method of lateral flexion-extension radiographs. They were aligned to superimpose VBs to determine the presence or absence of motion. Each operative segment was deemed fused if there was less than 2° of segmental movement on lateral flexion-extension views and if less than 50% of the anteroposterior distance of the interface between the endplates and the implants was radiolucent. Two degrees of motion were used as the upper limit to compensate for experimental error and variation (Fig. 2).

Analysis of the position of the implant considered subsidence (migration of the graft into the superior and/or inferior VB of >2 mm) and significant graft extrusion (>2 mm). In the iliac crest autograft group, radiographs were also studied for graft collapse.

All patients underwent 3-month clinical follow-up examination as well as extensive reassessment at 1 year postoperatively.

Lateral flexion-extension radiographs obtained 1 year following ACD and RTC fusion, demonstrating no signs of motion in the surgically treated segment.

The Mann-Whitney rank-sum test was used to analyze differences in the preoperative clinical and demographic characteristics (age, duration of symptoms, VAS score, and Nurick grade) and in clinical outcome variables between groups (Odom criteria, PSI, motor and sensory deficit improvement, VAS score, and Nurick grade). The Wilcoxon signed-rank test was used to analyze intragroup change. The Fisher exact test was used to analyze intergroup differences in fusion and implant-related complications. Statistical significance was set at p <0.05.