Total Disc Replacement
Total disc replacement is a surgical procedure to replace and mimic the function of the natural intervertebral disc. The procedure is currently performed for diseased cervical or lumbar intervertebral disk. The artificial disk replacement has the advantage of maintaining the mobility of the involved segment as compared to fusion surgery.
The intervertebral disk is a tissue present between adjoining vertebrae of the spinal column. The disks have a soft gel-like inner nucleus pulpous and a tough outer ring called the annulus fibrosis. The normal intervertebral disk acts to cushion the forces experienced by vertebrae and prevent them from grinding against each other.
With advancing age, the water content of the nucleus pulposus may decrease, making it more susceptible to injuries. Repetitive activities such as bending, turning, twisting may cause tears in the annulus causing the bulging of the nucleus pulpous through the annulus.
The herniated disk may compress upon the nerves/spinal cord/dural sac to cause radiculopathy. Obesity, smoking, and improper posture while sitting or standing also make the disks more vulnerable to injuries resulting in prolapsed intervertebral disks (PIVD). Lifting weights and traumatic injuries frequently result in PIVD.
The image above shows a total cervical disc replacement along with various parts of the cervical vertebra. The components of the total cervical disc replacement include metal parts attached on the adjoining vertebrae to create the space for the prosthetic disc. The prosthetic disc is usually made of a PEEK (poly-ether-ether-ketone) polymer.
The herniated disk is one of the leading causes of low back pain and radiating pain in the legs. Similarly, in the cervical spine, a prolapsed disk may cause neck pain and radiating pain in the arms. In severe cases, the herniation may result in weakness and numbness of the involved level.
Traditionally, surgical treatment for herniated disks has been done through the removal of the diseased disk and fusion of the adjoining vertebrae. The surgery is known to successfully alleviate the symptoms of the herniated disk in the neck or the lower back. However, due to the fusion of the vertebrae, the natural motion of the spine is lost in that segment.
Fusion surgery may therefore result in additional stress on the adjoining normal spine level. The additional stress may lead to increased wear and tear of various structures, known as degenerative spine disease. The loss of mobility is especially prominent in the neck, where patients may have limited motion while turning their heads.
Artificial disk replacement surgery prevents the complications of adjacent level degeneration and loss of movement. The total disk replacement surgery involves the removal of the diseased disk and bone spurs impinging on the nerves. The surgeon eases apart the vertebrae to create more space for the nerves.
The ends of the adjoining vertebrae are cleaned to prepare them for the disk insertion. The artificial disk is inserted in the natural space and the vertebral endplates hold the artificial disk in place. The position of the artificial disk is carefully inspected visually and with the help of an intraoperative X-ray.
The instruments shown in the image above are used during the surgery to remove the diseased disc, create raw bone surface for implanting the metal endplates and subsequent insertion of the prosthetic disc.
The trial cervical discs are used to find the correct size of the final cervical prosthetic disc for maximum stability and motion.
A rehabilitation period follows surgery and most patients are able to return back to their base activities in six weeks. The rehabilitation program focuses on strengthening the muscles of the neck or lower back after a period of healing.
Not all patients are candidates for an artificial disk replacement. Total disk replacement is indicated in the following patients:
- The intervertebral disk is the cause of symptoms as demonstrated by an MRI
- The symptoms result from the impingement of the involved nerve/spinal cord by the herniated disc.
- There has been a trial of conservative management in the form of therapy, NSAIDs, and heat/cold modalities.
- The symptoms have been present for more than 6 months.
- All other causes of symptoms have been ruled out.
A total disk replacement is contraindicated in patients suffering from osteoporosis, inflammatory spine diseases such as ankylosing spondylitis, rheumatoid arthritis, etc. The procedure is also contraindicated in patients with vertebral fractures, spine ligament injuries, or instability of the segment. Tumors, infections, and facet joint arthritis are also contraindications for performing total disk replacement.
A growing number of patients are undergoing cervical disc replacement or lumbar disc replacement. The procedure is successful to alleviate symptoms of radiculopathy from prolapsed intervertebral disk while maintaining spine biomechanics and motion.