Cervical artificial disc replacement: still experimental? Introduction and perspectives on cervical artificial disc replacement

Fernstrom spherical endoprostheses, utilized in the 1960s, may have been the first artificial discs implanted in humans. These were non-articulating, ball-bearinglike devices that replaced discs and preserved motion. In 1966, Fernstrom reported the use of these devices in the cervical, as well as the lumbar spine [1] (Fig 1). Modern cervical artificial disc replacement (C-ADR) first made its debut in 1991, with the Bristol/Cummins disc, the first of numerous articulating C-ADR devices (Fig 2). The original devices were implanted by Cummins in 20 patients, who later reported that some continued to function well, up to 12 years after implantation [2]. Results from these early articulating mechanical devices were encouraging, enough that further interest in these devices appeared very reasonable. Over the past 20 years, the number of cervical arthroplasty devices has proliferated and now are becoming available in various shapes, materials and biomechanical concepts. Current design concepts include metal-on-metal, metal-on-plastic, non-articulating metal bonded to plastic and plastic encased in cloth. The initial cervical arthroplasty devices implanted in the United States are now a decade old. While there are a few isolated reports of osteolysis, infection and implant failure due to wear, for the most part, these devices seem to have withstood the test of time, at least in the intermediate term. Whether they will continue to fare well and have longevity comparable to the initial hip arthroplasty devices remains to be seen. Fig 1 Fernstrom cage: this implant is widely considered to be the first disc implant and was a simple ball bearing adapted from use in the cervical and lumbar intervertebral discs. Fig 2 Cummins device: this design introduces an articulated coupling attached to the vertebral bodies with plate and screw fixation. It was modified and reintroduced as the Prestige II disc. 6 Similar to large joint arthroplasties performed on hips and knees, the differences in outcomes and revision rates for spinal arthroplasty will likely not be measurable in increments of a few years but will manifest themselves after decade-long intervals. While there are interesting similarities to the concept of hip and knee replacements, there are important differences to consider: • Unlike hips and knees, disc arthroplasties are not sy-novial joints. • Unlike hips and knees, a reasonable surgical alternative does exist—fusion surgery. • Unlike hip and knee surgery, continued motion in an intervertebral segment may lead to a recurrence of symptoms by overgrowth of bone and fibrous tissue …