Subsidence in Single Level Cervical Disc Arthroplasty

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Introduction Motion preservation with cervical disc arthroplasty implants has consistently been shown, in numerous randomized controlled trials, to produce equivalent or superior clinical outcomes to anterior cervical decompression and fusion. Therefore, there has been a call, within the spinal surgery community, to compare outcomes between arthroplasty implants. Although it is important to evaluate positive outcomes, it is also of vital importance to analyze complications and assess the potential influence of different implant designs on complications. We have experience in a large series of using several different arthroplasty implants. We have reviewed our series and have identified implants that have subsided. We provide a commentary on these cases. Material and Methods A retrospective review of all single-level anterior cervical decompression and disc arthroplasty cases, performed at the authors' institution, between 2006 and 2012 was conducted. Postoperative X-rays were assessed for any degree of subsidence compared with immediate postoperative X-rays. Cases with evidence of subsidence were studied for potential implicated factors. Results A total of 157 cases were reviewed consisting 64 PRESTIGE LP Cervical Disc System (Medtronic, Minnesota, United States), 51 NUNEC Cervical Arthroplasty System (RTI Surgical, Inc., United States), 35 Discocerv (Scient'x-Alphatec Spine, Arras, France), and 7 other implants in small numbers. Overall, 11 (7%) cases showed evidence of implant subsidence—two (3%) PRESTIGE LP, five (10%) NUNEC, and four (11%) Discocerv. In the cases that subsided, there were three males and eight females. There was a following variety of location of subsidence: anterior, posterior and complete surface of the implant, superior, and inferior. Seven of the cases did not fully cover the disc space in the anteroposterior plane. Three cases appeared to have been impacted into osteophytes posteriorly but subsidence was not necessarily in this location. The majority of cases appeared to have abnormal motion/spondylotic changes in adjacent levels, raising the possibility of abnormal forces being placed through the replaced level. Conclusion Cervical disc arthroplasty implant subsidence may be influenced by implant design, patient factors, and surgical technique. In this series, because of the small number of cases that showed subsidence, we cannot draw any firm conclusions. This report nevertheless should serve as an important stimulus for discussion and development regarding modifiable factors implicated in complications such as device subsidence.