Artificial disc replacement, also referred to as disc arthroplasty or total disc replacement, is an alternative to spinal fusion that involves removing a damaged disc and replacing it with an artificial implant. The artificial disc is able to retain the original bending and rotating motion of the spine.

Many artificial discs are designed to operate like a ball and socket joint. Take for instance the Mobi-C® Cervical Disc by Zimmer Biomet and the Prodisc® L Lumbar Disc by Centinel Spine, shown below. Both have a top and bottom metal plate that affixes to the vertebrae and a middle plastic insert that allow the plates to glide forward and back, side to side and rotate.

Mobi-C® Artificial Disc. ©LDR Spine, USA Inc.

Prodisc® L. © 2020 Centinel Spine

Life Span of an Artificial Disc

In the area of medicine, artificial discs are still relatively new, with the first artificial disc being approved for use in the United States in 2004. However, artificial discs have been used successfully in Europe since the 1990’s. This means some of the oldest artificial discs currently in use are at most 20 to 30 years old.

The materials, engineering, and implantation techniques used in the new discs are far superior to when the discs first arrived in the early 2000’s. However, as with any man-made device that is subject to wear and tear from repetitive forces like those experienced during everyday activities like running, exercising or playing sports.

Artificial Discs vs. Knee Replacements

Artificial disc replacement has trailed hip replacement and knee replacement for decades. Part of the issue is the knee and hip joints are more easily accessible than having to work around internal organs to reach the front of the spine to install an artificial disc. Secondly, if there is a problem with the disc, or if it wears out and needs to be replaced, revision surgery for an artificial disc is far more complex than revising a hip or knee joint — especially when the patient is over age 70 when the disc wears out.

This explains why orthopedic surgeons try to delay knee replacement and hip replacement surgery until the patient is in their 50s or 60s and the pain is unbearable. The surgeon hopes the artificial knee or hip joint will last 15 to 20 years — perhaps long enough to outlive the patient. This also underscores why an orthopedic surgeon will mandate that a joint replacement patient lose weight before surgery as the extra weight on an artificial knee or hip will wear it out early, perhaps in as few as 10 years if the person is obese or morbidly obese. With half of the U.S. population classified as “overweight” and 25% of Americans classified as obese, this is a huge factor is estimating the life of an artificial joint.

With artificial disc surgery, it’s not unusual for a person can have a blown disc in their neck or back in their 20s or 30s. This creates a huge issue with deciding on if artificial disc surgery is appropriate.

It is important to note that the knee experiences significantly different forces compared to a low back or neck, but similar considerations must be made by the physician and the patient before deciding if artificial disc is the appropriate option.

Longterm Results Look Promising

Studies that have been conducted on the durability of artificial discs do look promising. According to International Society for the Advancement of Spine Surgery:

“Longer term follow-ups at 10 years have been reported in Europe, demonstrating durability of lumbar arthroplasty. Lemaire et al reported on 100 Charite patients with minimum 10 year follow-up. Clinically, 62% had an excellent outcome, 28% had a good outcome, and only 10% had a poor outcome. Of the 95 patients eligible to return to work, 91.5% did so. These outcomes compare favorably with results described in the literature for fusion for lumbar [degenerative disc disease].” ( . . . )

“Based on a thorough review of the best available evidence-based scientific literature the International Society for the Advancement of Spine Surgery concludes that lumbar TDR is not new, experimental, or investigational. It is a well-tested technology which should predictably lead to better outcomes and less complications than fusion surgery, as well as a protective effect on adjacent levels.” ( . . . )

“There are now several long-term prospective and retrospective studies available on lumbar TDR which provide objective evidence regarding their safety and effectiveness. Data from prospective randomized clinical trials have reported consistently low rates of re-operations, and extremely low levels of particulate wear debris complications. ( . . . ) Based on sound analysis of the scientific literature, the International Society for the Advancement of Spine Surgery recommends universal coverage for single level lumbar TDR in patients meeting the established selection criteria.”

Additional follow-up studies have been conducted for many of the popular artificial discs on the market that consistently show the good durability of disc components, low rates of wear and tear and comparable – and often favorable – results as compared to spinal fusion.

Disc manufacturers are able to test their implants in the lab, simulating decades worth of movement in an average person. Zimmer Biomet, the manufacturer of Mobi-C® Artificial Disc says:

Every Mobi-C tested in the lab completed 10 million movement cycles, all demonstrating low wear rates. During this testing there were:
— No mechanical failures.
— No significant damage to the polyethylene insert or the metal plates.
— No major biomechanical issues.

( . . . ) Zimmer Biomet cannot predict the Mobi-C life expectancy for each patient. However, Mobi-C has been implanted over 70,000 times, in the U.S. since 2006 and in Europe since 2004.

Artificial Disc Revision Surgery

Just as a second knee replacement is far more complex than the first surgery, removing a worn out artificial disc is even more complex. That’s because the artificial disc is installed in a way to prevent it from slipping out of place. The mechanical disc design can feature ridges in the top or bottom of the disc that when tapped into place, it stays in place.

This is all good and fine until the day that disc needs to be removed because the rotational components have worn out. In revision surgery, the spine surgeon then may have to perform a “corpectomy” where a piece of the vertebrae is removed to extricate the old artificial disc. Installing the second replacement disc similarly can involve more challenge than the initial installation.