Artificial Disc Versus Fusion: A Prospective, Randomized Study With 2-Year Follow-up on 99 Patients

Rick C. Sasso, MD; Joseph D. Smucker, MD; Robert J. Hacker, MD; John G. Heller, MD

Disclosures

Spine. 2007;32(26):2933-2940. 

In This Article

Discussion

Our study demonstrates significant improvement (investigational group vs. control group) in multiple outcome measures at 12 and 24 months, including NDI, neck pain VAS, arm pain VAS, and SF-36 Physical Component Score. Although both surgical groups had statistically significant improvement in all outcome measures at 24 months with respect to their preoperative scores, the outcome-based group to group comparison at the follow-up intervals is highly suggestive of the benefit of the investigational implant in the 24-month period examined by this study.

Our results with regard to surgical outcomes are similar to those of other investigators and represent the largest single randomized, controlled, prospective series of patients with Bryan disc arthroplasty followed to 24 months. Goffin et al[13] reported early results of a multicenter study of the Bryan disc performed at single levels in 60 patients for the treatment of radiculopathy or myelopathy due to disc herniation or spondylosis failing at least 6 weeks of conservative treatment. Exclusion criteria included previous cervical spine surgery, axial neck pain as the sole symptom, significant anatomic deformity, and radiographic evidence of instability (translation >2 mm or >11° of angulation compared with the adjacent level). Patient outcomes were determined by the Cervical Spine Research Society and SF-36 instruments. Clinical success rates at 6 months and 1 year were 86% and 90%, respectively, exceeding the study's targeted success rate of 85%.

In a separate report, Goffin et al[15] have recently published the intermediate-term results of this multicenter study. The study was expanded to include a second arm evaluating the treatment of 2 adjacent levels. The single-level arm had 103 patients enrolled with 100 reaching the 1-year mark and 51 reaching 2-year follow-up. The bilevel study arm was comprised of 43 patients with 1-year data completed on 29 patients and 2-year data available on 1 patient. Success rates in the single-level study at 6 months, 12 months, and 24 months were 90%, 86%, and 90%, respectively. In the bilevel study, the success rate at 6 months was 82% and 96% at 1 year. No device failures or subsidence was observed in any patient. At 1-year follow-up, flexion-extension range of motion per level averaged 7.9° in the single-level arm and 7.4° in the bilevel arm.

Anderson et al described the follow-up results of 73 patients who had >2-year follow-up status on a 1-level Bryan disc arthroplasty.[14] Forty-five of these patients were rated as excellent, 7 as a good, and 13 as fair. Only 8 patients had a poor rating at the 2-year follow-up. SF-36 functional outcome data demonstrated significant improvement from preoperative to 3-month postoperative time points. These outcomes remained stable 24 months after surgery. There was no radiographic evidence of subsidence of implants. A total of 89% of all patients had at least 2° of motion at 1 and 2 years. Average range of motion was 8°. There was 1 early anterior device migration associated with a partially milled cavity.

Sekhon[16] reported early results of 9 patients with cervical spondylotic myelopathy who were treated with anterior decompression and reconstruction with the Bryan disc. Follow-up ranged from 1 to 17 months. On average, the Nurick grade improved by 0.72 and Oswestry NDI scores improved by 51.4 points. Improvement in cervical lordosis was noted in 29% of the patients. No complications were reported.

In another small prospective study, Duggal et al reported on 26 patients undergoing single- or two-level implantation of the Bryan artificial cervical disc for treatment of cervical degenerative disc disease resulting in radiculopathy and/or myelopathy.[17] Patients were evaluated radiographically and via NDI and SF-36 at regular intervals. Segmental sagittal rotation from C2-C3 to C6-C7 was measured using quantitative motion analysis software. A total of 30 Bryan discs were placed in 26 patients. Follow-up duration ranged from 1.5 to 27 months, with a mean duration of 12.3 months. A statistically significant improvement in the mean NDI scores was seen between preoperative and late postoperative follow-up evaluations.

Several complications were observed in our investigation: 4 control, 2 investigational. In the investigational group, 2 patients went on to require surgical intervention at adjacent levels for symptomatic pathology refractory to nonoperative means. In the control group, 2 patients required surgical intervention at adjacent levels, 1 patient required surgical revision for nonunion, and 1 patient required supplemental posterior cervical fusion. Our complications may be compared with those described in the series reported by Goffin et al. In the single-level study,[13] 3 patients required subsequent surgical intervention. These procedures included the evacuation of a prevertebral hematoma, a posterior foraminotomy for residual compression, and a posterior laminectomy for residual myelopathy. Four subsequent procedures were required in the bilevel study: evacuation of a prevertebral hematoma, evacuation of an epidural hematoma, repair of a pharyngeal/esophageal injury caused by intubation, and an anterior decompression due to residual nerve root compression. Two patients developed dysphonia after second procedures. One patient initially had a device placed at a wrong level and developed temporary dysphonia after a device was placed at the appropriate level. The other patient developed a second symptomatic disc 21 months after the index procedure and developed severe dysphonia from bilateral vocal cord paralysis after a second device was placed from a contralateral approach.

In the intermediate Goffin et al study,[15] temporary anteroposterior device migration was detected in 1 patient and suspected in another. This migration was felt to be due to inadequate endplate milling early in the study. This issue was corrected with modification of the instrument system. Migration >3.5 mm, the radiographic threshold of segmental stability, was not observed.

While it is difficult to draw statistically relevant conclusions from few reoperative complications observed in our series, it is probable that the long-term follow-up of this cohort will yield further data. In the interim, reoperative rates have been reported in other series and are relevant to the discussion.

Anderson et al[18] studied reoperation rates following arthroplasty and cervical spine arthrodesis. Their randomized, prospective, controlled study analyzed data from multiple IDE trials including: U.S. PRESTIGE and Bryan IDE trials, European Bryan (single-level), and PRESTIGE trials. Additional arthrodesis data were obtained from the control group of the AFFINITY Cervical cage. A total of 649 arthroplasties and 580 control arthrodesis patients were analyzed.[18] The follow-up period for the arthroplasty and arthrodesis groups was comparable and ranged from 6 weeks to 28 months. Among the arthroplasty patients, there were 12 (1.8%) reoperations out of 649, with 10 (1.5%) at the same level, and 4 (0.6%) at another level (some pts had a redo at the same level plus another level done). In the arthrodesis group, 21 (3.6%) underwent a reoperation. 9 (1.6%) were at the same level, and 13 (2.2%) were at a different level. The difference in reoperation rates was just less than significant (P = 0.055). Reoperations at the treated level were similar but reoperations at an adjacent level were significantly higher for the arthrodesed patients (P = 0.01). Their results suggest, in the short-term (follow-up <28 months), reoperations are more common following arthrodeses than arthroplasties of the cervical spine. This was thought to be due to a greater number of reoperations at adjacent levels following arthrodesis.[18]

One of the primary goals of cervical disc replacement is to reproduce normal kinematics after implantation. Our investigation noted preservation of angular motion at the target level at 24 months. This statistically significant finding mirrors the findings of other investigators. Duggal et al have demonstrated preservation of motion in Bryan treated spinal segments (mean range of motion, 7.8° for up to 24 months postsurgery).[17] The relative contribution of each segment to overall spinal sagittal rotation differed depending on whether the disc was placed at C5-C6 or C6-C7. Overall cervical motion (C2-C7) was moderately increased on late follow-up evaluations.[17]

A few retrospective evaluations of patients with cervical myelopathy treated with anterior decompression and artificial disc replacement are available. Results from these studies are favorable. It does appear that patients with cervical myelopathy may be treated with a cervical disc replacement and experience successful outcomes. Sekhon[16] concluded that, at least in the short-term, cervical myelopathy treated by Bryan cervical disc arthroplasty resulted in excellent outcomes.

Bertagnoli et al reported on the early results after ProDisc-C (Synthes Spine, Inc., West Chester, PA) cervical disc replacement.[19] Patients with mild myelopathy were included; however, severely myelopathic patients were excluded. The conclusions were that mild myelopathy can be satisfactorily treated with cervical arthroplasty.[19]

The closest look at the use of artificial disc replacement for the surgical treatment of myelopathy is by Riew et al who undertook a prospective, randomized, multicenter investigation to determine the effectiveness of cervical arthroplasty for cervical myelopathy.[20] The patients were a subset of those enrolled in the FDA IDE study for the Bryan and Prestige artificial cervical disc replacements. All patients with a diagnosis of myelopathy were evaluated. Myelopathy was defined as hyperreflexia or clonus or Nurick grade ≥1. None of these patients had retrovertebral cord compression from pathologies such as ossification of the posterior longitudinal ligament. Of the 542 patients in the Prestige trial, 108 had myelopathy. Fifty-eight of these were randomized to arthroplasty while 50 underwent an ACDF. Of these, 55 arthroplasty and 39 ACDF patients had a minimum 1-year follow-up; 11 arthroplasty and 14 ACDF patients had 2-year follow-up. Of the 465 patients in the Bryan trial, 93 had myelopathy. Forty-nine of these were randomized to arthroplasty, while 44 underwent an ACDF. Of these, 42 arthroplasty and 32 ACDF patients had a minimum 1-year follow-up; 18 arthroplasty and 15 ACDF patients had 2-year follow-up.

By 12 months, gait improved for both the arthroplasty and arthrodesis groups. In the Prestige study, 39% of the arthroplasty and 33% of the ACDF patients had improvement in their gait. No one in either group had clinical deterioration and 61% of the arthroplasty and 67% of the ACDF group had maintenance of their gait. Of the patients with 2-year follow-up, 46% versus 50% (arthroplasty vs. ACDF) noted improvement, 54% versus 50% noted maintenance of their gait, and there was no clinical deterioration in either group. Arm and neck pain VAS scores, NDI, and SF-36 Physical and Mental Component Scores all improved from baseline at 6, 12, and 24 months. There was no statistically significant difference between the arthroplasty and arthrodesis groups. There were no revisions in the arthroplasty group while there was 1 removal and 1 reoperation (foraminotomy) in the ACDF group.

In the Bryan study, 45% of the arthroplasty and 30% of the ACDF patients had improvement in their gait. No one in the arthroplasty group deteriorated clinically, while 1 in the ACDF group worsened; 55% of the arthroplasty and 67% of the ACDF group had maintenance of their gait. Of the patients with 2 year follow-up, 50% versus 38% (arthroplasty vs. ACDF) noted improvement, 50% versus 62% noted maintenance of their gait, and there were no deteriorations in either group. Arm and neck pain VAS scores, NDI, and SF-36 Physical and Mental Component Scores all improved from baseline at 6, 12, and 24 months. There was no statistically significant difference between the arthroplasty and arthrodesis groups.

The above results suggest that arthroplasty is equal to ACDF at treating cervical myelopathy. At 3, 6, 12, and 24 months, the improvement in gait, as well as all the various outcome measures, was equivalent between the arthroplasty and arthrodesis groups. These results suggest that, for focal retrodiscal pathology causing cervical myelopathy, arthroplasty is an effective treatment. It should be noted, however, that none of these patients had diffuse retrovertebral compression, such as from ossification of the posterior longitudinal ligament.

It is clear from preliminary studies that cervical myelopathy can be successfully treated by artificial disc replacement. It is extremely important, however, to understand the appropriate indications, and it is critical to recognize the contraindications for cervical arthroplasty. The suitable situation is quite narrow: a focal disc herniation without retrovertebral compression, without significant facet pathology, and without multilevel stenosis. The vast majority of patients with myelopathy are not candidates for cervical arthroplasty due to multilevel pathology or significant degeneration. Long-term follow-up studies are essential to fully understand the role of cervical arthroplasty. The FDA IDE studies of arthroplasty versus ACDF will eventually provide these important long-term data for us to understand the appropriate indications for this new technique.

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