How safe are the new disc replacements that can be put into the neck?
It's been 10 years since the first artificial disc was implanted in the cervical spine (neck). That event took place in Europe and quickly caught on in the United States. Now we have the four- and six-year results starting to trickle into the orthopedic literature.
Most people who have a cervical implant have degenerative disc disease with neck and arm pain along with neurologic symptoms such as numbness, tingling, weakness, and even paralysis. The condition has not responded to conservative (nonoperative) treatment. That's why surgery is considered next. And instead of having a neck fusion, which limits neck motion, disc replacement is now available for some patients.
Radiculopathy (nerve pain down the arm) or myelopathy (pressure on the spinal cord) are common with disc protrusion or herniation. Most of the patients getting a cervical disc replacement have single-level disc replacement. But it is possible to replace the discs with implants placed at two levels.
Early results reported are very positive after the first two years. X-rays are used to view the neck, discs, and motion at each involved level. The patients fill out valid and reliable surveys to indicate how well they are doing (motion, function, neck and arm pain or other neurologic symptoms).
As time goes by, the results have been tallied and reported. In one recent multicenter study, there was a high incidence of adverse events reported. This included things like pain in the neck and arm (shoulder to wrist), numbness and tingling in the arm, and hoarseness of the voice. A few odd events were reported such as low back pain and a soft tissue tumor in the neck. Those problems weren't likely caused by the implant but all complications are being investigated. The real area of interest (used as a measure of success or failure of the implants) was the number of second surgeries (reoperations).
Any time the device migrated (moved or shifted), put pressure on the spinal cord, or had to be removed for any reason, it was counted as a failure. Once removed, the neck was fused rather than trying another disc replacement. Some patients had a second surgery but it wasn't to remove the implant or correct problems related to the first procedure. These additional surgeries were to treat disc problems at other levels in the cervical spine. Overall, the number of second surgeries was low and the success rate reported as 93.9 per cent.
Comparing the results after six years with the early two-year outcomes, it looks like most patients were still doing well. Any reports of pain or discomfort at the end of two years were even better after six years. There were some changes in sensation noted around the end of the fourth year. No one was quite sure what that was all about or why it resolved over time, so it's something they will continue to investigate in future studies.
As with any surgical procedure, there can be problems related to the anesthesia, infections, wound healing, and blood loss. For now, all indications are that artificial disc replacement for the cervical spine is safe and effective. These are preliminary findings until long-term results can be reported after 10, 15, and 20 years.