Studies on Cervical Artificial Disc Replacement

Abstract: Artificial disc replacement (ADR) was developed as an alternative to anterior fusion after decompression for cervical degenerative radiculopathy. By preserving motion, it was expected to prevent acceleration of adjacent segment pathology (ASP) associated with fusion, and lead to better clinical outcomes. The aims of this thesis were to evaluate whether ADR surgery leads to better outcomes than fusion surgery, to investigate if it prevents the acceleration of ASP, and to analyze its potential complications.  In a multicenter randomized controlled trial (RCT) 153 patients were randomized to ADR (DiscoverTM implant) or fusion surgery (autograft, plate and screws). The outcomes at 5 and 10 years postoperatively were analyzed with Neck Disability Index (NDI) as primary measure. Heterotopic ossification (HO), ASP, and secondary surgery where analyzed. The measurements of radiographic parameters used in the assessment of cervical alignment where validated.To further analyze secondary surgery after ADR, a descriptive register cohort study was done with 42 patients whose data were retrieved from Swespine and completed with medical charts, images, and a telephone interview. There was no difference in NDI scores between groups in the RCT, 5 or 10 years postoperatively. Radiological and clinically significant ASP were similar in both groups. There was more secondary surgery in the ADR group compared with the fusion group, mainly due to device loosening in women. Severe HO was seen in 71% of the ADR implants 5 years postoperatively, and 27% were fused, male sex being a clear risk factor.Normative data for measurement error were provided on the cervical alignment measurements,  and the most reliable were the K-line tilt and the cervical sagittal vertical axis (cSVA). In the 42 patients in the register cohort study the most common diagnosis leading to reoperation was loosening of the ADR implant and/or ASP, predominantly treated with fusion surgery. Reoperation resulted in good outcomes in the vast majority of patients. At the long-term, there is no clinical benefit of ADR over fusion surgery after decompression for cervical degenerative radiculopathy. ADR, compared with fusion surgery, does not prevent acceleration of ASP, and results in more reoperations. Revision surgery for failed cervical ADRs is effective and justified.