Improvements Sustained 10 Years After Cervical Disc Replacement

Caroline Helwick

May 01, 2019

SAN DIEGO — Improvements were sustained at 10 years for patients treated with the Mobi-C cervical disc in the trial that led to its approval by the US Food and Drug Administration (FDA) in 2013, a new study shows.

This included maintenance of scores for pain, neck disability, and neurologic status, with no worsening of radiographic adjacent segment degeneration as compared with earlier follow-up. In addition, 98.4% of patients were still satisfied with the surgery 10 years later, researchers report.

"Our question was whether the improvements we see at 7 years were sustained further out, so we followed patients after the study was completed," Kee D. Kim, MD, professor and chief of spinal neurosurgery, University of California Davis, reported at the American Association of Neurological Surgeons (AANS) 2019 Annual Scientific Meeting. "We saw that CDA [cervical disc arthroplasty] patients continued to have sustained improvement at 10 years."

Short- and mid-term studies have shown the effectiveness of CDA to treat cervical disc degeneration. The purpose of this study was to analyze the 10-year outcomes of the multicenter experience in patients with CDA at 1 or 2 contiguous levels. Patients had degenerative disc disease refractory to nonsurgical treatment and no prior cervical operations, and they were randomly assigned 2:1 to CDA or fusion.

Upon completion of the 7-year study, follow-up continued at 10 years for consenting patients at nine high-enrolling centers. Outcomes included neck and arm pain (by visual analog scale [VAS]), neck disability index (NDI), neurologic status, patient satisfaction, secondary surgery, and adverse events. Radiographic endpoints included segmental and global range of motion (ROM), sagittal alignment, adjacent level degeneration, and heterotopic ossification.

Ten-year follow-up was obtained from 187 of 231 eligible patients (81%). Mean follow-up was 10.2 years and the longest follow-up was 11.2 years. Radiographs were obtained from 170 patients (73.6%) at 10 years. There were no significant differences in demographics or preoperative characteristics between the 10-year cohort and the original FDA cohort.

Numerous Improvements Maintained at 10 Years

Ten years after CDA, patients continued to show significant improvement from baseline, and some endpoints improved even further between 7 years and 10 years:

  • Sustained improvement was found for pain scores, NDI, and neurologic status.

  • Sagittal alignment improved after surgery and remained improved.

  • Radiographic adjacent segment degeneration at 10 years was not significantly worse at 10 years, compared with 5 and 7 years.

  • No subsequent surgery was deemed CDA-related.

  • ROM remained comparable to baseline.

For VAS neck pain, the 2-level group outcomes were significantly better at 10 years than 7 years (P < .01) whereas the 1-level group demonstrated a favorable trend (P = .07). VAS arm pain improved to a significant degree between 7 and 10 years in the 2-level group (P < .01) and remained stable for the 1-level group (P = .83).

Neck disability also sharply improved after CDA, and for the 2-level group it further improved significantly between 5 years and 7 years (P < .01); a similar favorable trend was shown in the 1-level group (P = .14).

Neurologic status improved significantly from baseline and this was sustained at 10 years. At baseline, 82% of patients had deficits, but this rate fell to 24% at 7 years and was sustained at 22% at 10 years (P = .70).

Segmental ROM (flexion, extension, lateral bending), both for 1-level patients and for 2-level patients, also was maintained at levels similar to baseline, as was global ROM.

Sagittal alignment significantly improved from baseline to 10 years for both 1- and 2-level groups (P < .001) and this was maintained at 10 years (P = .59, P = .61, respectively).

Adjacent Level Degeneration Not Worsened

Adjacent level degeneration was not worsened. "This is important. It’s what we really care about," Kim commented. "We feel a certain degree of protection is provided by placing an artificial disc instead of a fusion."

At 10 years, no significant worsening in grade 3/4 adjacent level degeneration was seen in patients with 1-level CDA, as compared to 5 years (P = .35) or to 7 years (P = .84). No changes were seen in the 2-level group at 10 years, vs 5 years (P = .66) or 7 years (P = .63).

Similarly, as expected, some heterotopic ossification was observed, but there were no significant changes in grade 3/4 events between 7 and 10 years for 1-level (P = .88) or 2-level CDA (P = .70).  

For all CDA patients, 5.1% required subsequent surgery at the index level and 4.7% required it at an adjacent level at 10 years. As compared with surgery occurring at 7 years, this represented only one new subsequent case at the index level (at 9.5 years after CDA) and it was deemed unrelated to the original implant. 

"You see that fusion patients are twice as likely to have additional surgery and more than twice as likely to have another surgery at an adjacent level," Kim noted.

At the 10-year follow-up, there were 6 new adverse events reported as possibly related to the CDA device, including 5 cases of heterotopic ossification and 2 cases of subsidence. None required surgical intervention. Patient satisfaction with disc surgery remained very high out to 10 years, reported by 98.4% of Mobi-C recipients.

"These patients are now in their mid-50s. We don't know what will happen in their 60s and 70s, but at 10 years CDA patients continue to have sustained improvements," Kim concluded. "Our results through 10 years demonstrate that CDA with Mobi-C continues to be a safe and effective surgical treatment for patients with 1- or 2-level cervical degenerative disc disease."

Patient Selection Important

Craig A. VanDerVeer, MD, a neurosurgeon practicing in Charlotte, North Carolina, commented on the findings for Medscape Medical News. "We have used this device very successfully. In fact, I use it preferentially in patients who are fairly young and have cervical disc rupture," said VanDerVeer. 

"We need more time to follow up, but it appears that this does prevent adjacent level disease, which is the big problem with fusion," he said. "The constant refrain is, 'Is the adjacent level disease from continued degeneration of the disc space that will be there in spite of fusion? Or can we ameliorate the changes by preserving a little bit of motion?' "

"The rate of adjacent level disease increases with the number of levels you fuse, so by protecting motion and the ability to have three or four degrees of motion at a disc space — we think this is protective because it allows less strain at adjacent levels," VanDerVeer continued. "I think more time will provide more data that increases that opinion."

VanDerVeer added that his practice now limits the use of CDA to patients he and his colleagues predict will derive the greatest benefit.

"Just coming into our office and saying, 'I have cervical spondylosis and a disc rupture and I want an artificial disc' will not get them one," he said. "We will look at their X-rays and determine if they are good or poor candidates. We won’t put this in if you’re a poor candidate. We now have a wide-ranging tool kit to deal with different conditions. That’s the granularity of determining who would benefit the most."

Zimmer Biomet sponsored the Mobi-C® cervical disc FDA clinical trial and contributed to the design and conduct of the study and provided assistance with analysis of data. The authors reported receiving assistance from Zimmer Biomet for the preparation of this presentation. Kim disclosed no other relevant financial relationships. VanDerVeer has disclosed no relevant financial relationships.

American Association of Neurological Surgery (AANS) 2019 Annual Scientific Meeting: Abstract 303. Presented April 17, 2019.

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