Spinal Disc Replacement

Spinal disc replacement with the CHARITÉ Artificial Disc

Introduction to artificial discs

In October 2004 the CHARITÉ™ Artificial Disc was the first disc approved for disc replacement use in the general population of back pain patients in the U.S. There is a great deal of interest in the medical community and among back pain patients regarding the potential of artificial discs for lumbar disc replacement. But despite all the publicity, it’s important to remember that artificial discs are not a miracle cure. Like any medical treatment for low back pain, lumbar artificial disc replacement surgery has both good potential and some considerable risks. Given that artificial discs are still a relatively new technology and procedure, disc replacement surgery also has a number of unknown risks.

To date, ongoing low back pain from degenerative low back conditions that does not get better with non-surgical care has been treated with some type of lumbar spinal fusion surgery. It is important to note that modern spinal fusion techniques and technologies have dramatically improved the outcomes of fusion surgery in recent years. When spine fusion surgery is done for the right indications by an experienced spine surgeon, it is generally a very reliable surgery.

However, spine fusion does change the mechanics of the segment of the low back that is fused. One major intended benefit of artificial disc replacement (ADR) surgery over spine fusion is that it does not change the biomechanics of the lower spine, allowing the spine to maintain its normal range of motion and thereby reducing or eliminating the risk of degeneration in adjacent segments of the spine.

The CHARITÉ Artificial Disc (DePuy Spine, Inc., a Johnson and Johnson company), is composed of two metallic endplates and a polyethylene core that moves between them. During the surgery, the patient’s degenerated disc is removed and a pair of endplates made of cobalt chromium are inserted in the space between the vertebrae and attached to the vertebrae above and below the disc. A polyethylene material is then inserted between the plates to create a disc-like structure that mimics the normal disc by providing both a normal level of separation between the vertebrae and allowing the usual range of motion and flexibility for that segment of the spine.

While this article reviews the CHARITÉ disc prosthesis (see Figure 1),there are several other artificial discs that have been developed and are currently in clinical trials in the U.S. or are in the process of development.

The CHARITÉ Artificial Disc was approved for use in the U.S. in October 2004, but variations of the CHARITÉ disc replacement technology have long been in use in other countries and the CHARITÉ Artificial Disc replacement procedure is now available in more than 30 countries. Prior to approval for use in the U.S., approximately 95% of all procedures for the CHARITÉ Artificial Disc device were done in the United Kingdom, France, Germany, and the Netherlands.

Theoretical advantages of the CHARITÉ Artificial Disc

The CHARITÉ disc implant is designed to mimic the functionality of the patient’s own intervertebral disc (see Figure 2). The prosthesis is intended to maintain the normal movement between the vertebral bodies and prevent them from collapsing (and thereby irritating or damaging the nerve root) by maintaining the disc space height between the bones.

One of the main theoretical advantages of artificial discs (vs. spine fusion surgery) is to preserve the mobility of the patient’s adjacent discs and delay the onset of arthritic changes adjacent to a fused level. The procedure can be a substitute for spinal fusion, which eliminates the motion from a painful motion segment by fusing the vertebrae together. Spinal fusion does tend to place increased stress on the adjacent vertebral segments.

Theoretical disadvantages of the CHARITÉ Artificial Disc

Since artificial hips and knees were introduced in the 1960’s, doctors have explored the idea of prosthetic replacements for damaged or degenerated intervertebral discs. The disc is a very complicated joint, so the engineering challenge to partially or fully replace a disc is considerable. Also, because disc injury is a common cause of back pain in younger adults (age 30 to 50), an artificial disc needs to be designed to last for decades. The demands on a lumbar artificial disc will be very great and may not outlast the lifetime of the patient - meaning patients may need revision surgery. And because of the nearby vascular structures and scar tissue from the original surgery, revision procedures for a lumbar artificial disc can be very dangerous.

The outcome of any treatment, especially surgery, relies on the accurate or precise diagnosis of the source of pain. There are also psychological, physical, and social factors involved in the successful treatment of chronic pain. Collectively, these are known as surgical indications. Diagnostic procedures, spine imaging, surgical indications, and surgical techniques have been refined over the years so that experienced spinal practitioners can reliably and predictably achieve excellent clinical outcomes with modern spinal fusion surgery. Because it is a new technology, the indications, as well as the type of disc replacement implants, are quite specific.

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