Spine Education

Cervical Artificial Disc Replacement

Just as orthopedic surgeons have replaced worn out hips, knees, and other joints in the body, surgeons now have the technology to replace worn out discs in the low back (lumbar spine) and neck (cervical spine). The Food and Drug Administration (FDA) recently approved an artificial disc for the lumbar spine, and surgeons await approval of other artificial discs for both the lumbar and cervical spines. European surgeons have implanted artificial discs in the cervical spine for several years with good results, and some U.S. surgeons have implanted many of them as a part of clinical studies to test their safety and effectiveness. Early results from these studies are promising. Overall, patients with disc replacements in the cervical spine have had improvement in arm pain and neck pain, and they are generally pleased with the procedure.

Although discs in the cervical spine often wear out with age, most "bad" discs do not warrant any treatment at all. In fact, symptoms usually improve with time. Some degenerative discs herniate disc material from tears in the disc wall (annulus), and some develop bone spurs (osteophytes) near nerves as they exit the spinal cord. When these nerves are compressed, patients may experience any combination of arm, shoulder, or neck pain. Patients may also feel numbness or tingling sensations in their fingers, hands, or arms. Certain muscles may feel weak. Typically, over-the-counter anti-inflammatory medicines, physical therapy exercises, and cervical traction often alleviate these symptoms. Other types of medicines and treatments may decrease the pain, numbness, and weakness as well.

For those patients who do not gain relief of their symptoms, surgeons have historically recommended an operation where the herniated disc or bone spurs are removed. Spine surgeons usually perform this operation through an incision on the front of the neck. Once the disc is removed and the nerve is freed from its compression, surgeons place bone graft between the two spine bones once occupied by the disc to maintain height of the disc space and to facilitate a fusion between the bones. Most surgeons now place a plate with screws on the bone to maintain stability until the body grows its own bone, a process which takes a few months. This procedure is called anterior cervical discectomy and fusion (ACDF).

Although success rates for ACDF are greater than 90%, many surgeons believe that the fusion itself causes abnormal stress and motion to occur at adjacent levels in the cervical spine, which may lead to accelerated degeneration at these neighboring levels. Although it is safe and effective to repeat the operation at another level at a later time, some spine surgeons claim that a disc replacement may be a better treatment for some patients.

In a disc replacement operation, which is also performed through an incision on the front of the neck, spine surgeons perform many of the same steps as those performed in an ACDF; specifically, they still take out the disc and remove the offending tissue which compresses the nerve. However, instead of placing a bone graft and fusing the two vertebral bones together, the disc is replaced with an artificial disc which preserves motion. With a motion-sparing device like an artificial disc replacement, the adjacent levels of the cervical spine undergo more normal motion. Consequently, adjacent discs should not wear out at accelerated rates.

Not all patients who would benefit from an ACDF are good candidates for a disc replacement. Since success and safety of the procedure rely on excellent bone quality to maintain the position of the artificial disc, some patients with osteoporosis may not be eligible for an artificial disc. Additionally, if patients have a significant component of pain from other parts of the cervical spine besides the disc, such as the facet joints, then an ACDF addresses those symptoms better.

Stephen M. Hansen MD, MBA is currently a spine fellow at Indiana Spine Group, Indianapolis, IN; His practice will be with Harbor Orthopedic and Fracture Clinic in Aberdeen, Washington.

Rick C.Sasso MD, Indiana Spine Group, Indianapolis, IN; Assistant Professor, Indiana University School of Medicine.