Intervertebral disc arthroplasty

The first artificial disc was implanted in 1959, with Swedish surgeon Ulf Fernström publishing a description of his experience implanting a stainless-steel ball bearing into an intervertebral disc space after discectomy in 1966. Fernström balls, used in approximately 250 patients, created segmental hypermobility and demonstrated a marked tendency to settle into the vertebral endplates. Reports suggest that function, while initially good, degenerated over time.

During the 1970s, a new concept was introduced: achieving mobility through articulation between the concave and convex surfaces of a multi-component device. Designs patented at that time combined metal, ceramic, or other types of elastic bearings with components made of silicone composites, rubber, polyurethane, plastics, or fluid-filled membranes. Some designs incorporated balloons, cages, pegs, wire screens, hinged plates, or springs. Springs proved to be particularly impractical because they could not withstand biomechanical fatigue tests of stress and strain.[18]

The first design with wide clinical adoption was the Charité disc replacement, designed by East German scientists: two-time Olympic champion in women's artistic gymnastics Karin Büttner-Janz and Kurt Schellnack, a doctor, engineer, and professor—both of whom were affiliated with the Charité Center for Musculoskeletal Surgery at the Medical University of Berlin[2]. First implanted in 1984, the disc had a biconvex polyethylene nucleus within a radiopaque metal ring that interfaced with two cobalt-chromium-molybdenum alloy endplates, which were coated with calcium phosphate. Approved for use in the United States in 2004, after a 4-year clinical trial, Charité was removed from the market by 2012.

The second disc replacement to achieve wide clinical use was the prodisc total disc replacement; it continues to have worldwide use today. Designed by French orthopedic spine surgeon Thiery Marnay, M.D., in the late 1980s, early implantations of the prodisc device began in 1990, with a 7-11 year follow-up published in 2005. After implementing design changes to the bone-facing endplate, and after a clinical study in the United States, the new design was made available worldwide. In October 2001, as part of the FDA trial, Jack Zigler, M.D., a spine surgeon at Texas Back Institute in Plano, Texas, performed the first prodisc L artificial disc replacement in the United States.

The US FDA requires manufacturers to conduct clinical studies to assess the safety and efficacy of disc replacements before obtaining approval to market the devices in the United States. Other devices can be approved for use with simpler non-clinical reviews. As a result, disc replacements have the highest level of clinical evidence of any spine devices. However, since this research is funded by industry, some controversy over data bias produced by the clinical studies exists [see Controversy].

Level 1 and level 1a studies (the highest quality levels: see Hierarchy of Evidence) have shown safety and efficacy for both lumbar and cervical discs, and have become the de facto standard of care for appropriate patients outside of the United States.[19][20] All prospective, randomized clinical studies that have been run in the United States have shown lumbar and cervical disc replacements to provide faster recovery, better long-term patient satisfaction, and fewer incidents of adjacent segment degeneration than comparative spinal fusion options.[19][20]

A few non-industry funded studies also exist. In addition to the previously mentioned 7-11 year followup study on prodisc conducted by Thiery Marnay, M.D.,[21] a Norwegian study published in The Spine Journal in 2017 compared total disc replacement and multidisciplinary rehabilitation with an eight-year follow up. The study was randomized, controlled, multi-center and not funded by industry. 77 patients randomized to surgery and 74 patients randomized to rehabilitation responded at eight-year follow-up. The study found a statistically significant benefit in favor of surgery.[22]

The AAOS states that disc replacement requires a high level of technical skill for accurate placement and has a significant level of risk if revision surgery is needed.[23]

Members of AAOS and the American Association of Neurological Surgeons joined together as the Association for Ethics in Spine Surgery, formed to raise awareness of the ties between physicians and device manufacturers.[24]

Aetna rescinded its positive coverage for single level lumbar ADR after merger with Coventry in 2013.[25] There is currently (in 2022) a class-action lawsuit against Aetna Life Insurance for denying patients seeking lumbar disc replacement surgery in the United States alleging that patients are being harmed by denials since Aetna has declared them 'experimental or investigational’.[26]

Despite published meta-analyses (the highest-level clinical evidence) that have illustrated that total disc replacement seems to be superior to fusion in most clinical parameters, new studies have identified concerns regarding long-term durability of some of these devices. One such recent study identifies a large “midterm failure rate” related to the M6-C. It recommends that “patients implanted with the M6-C prosthesis should be contacted, informed, and clinically and radiologically assessed”.[27] Unfortunately, catastrophic failure of the M6-C prosthesis has also been reported.[28]