Conquer Back and Neck Pain - Walk It Off! (30 page)

The exciting new approaches for treatment of back pain are focused on replacing or repairing a painful and worn-out disc. The three major approaches are: 1) to replace the worn-out disc with an artificial disc; 2) transplant a healthy disc to replace the worn-out disc; or, 3) repair the disc using gene therapy.

Fusion of a disc space in the neck and low back is associated with accelerated breakdown of adjacent discs. In order to avoid this problem, it is theoretically advantageous to restore normal motion in the abnormal disc by replacing or repairing it.

Artificial disc replacement is the most developed of the attempts to restore the normal motion and weight bearing of a worn-out disc. In 2006, the first lumbar disc replacement was approved by the U.S. FDA. Throughout the world, more than 10,000 patients have had this model of artificial disc placed in their low back. There are at least 10 other models of artificial discs being used throughout the world. At a recent seminar on innovations in spine surgery, I heard several discussions concerning the artificial disc. During the meeting I wrote down the following notes regarding disc replacement: “limited indications, technically difficult to perform, potential life-and limb-threatening complications, fixing failures is difficult, if a spinal fusion is required to repair a failed procedure it is difficult to perform, and the results of the fusion are not as good as would be expected.” I then heard a lecture from a spinal surgeon, whom I respect, on his experience with treating more than 100 patients with an artificial disc.

The ideal candidate for a lumbar disc replacement, according to this experienced surgeon, is a 40-year-old female who needs one moderately degenerated disc replaced because of back pain that has lasted more than one year despite treatment. She has no leg pain, is moderately active, and has not had previous surgery. In addition, the patient should be in good health, of normal weight, and a non-smoker. As you can imagine, there are very few people who fit into this description! He went on to say that people who are not good candidates for a disc replacement have some combination of the following: multiple degenerated discs; inactive lifestyle; overweight; have a herniated disc squeezed into the spinal canal causing leg pain; had previous abdominal or pelvic surgery; are over 60 years or under 21 years of age; is a smoker; and, have spinal stenosis, spondylolisthesis, scoliosis, facet joint arthritis, osteoporosis, or vascular disease. The list goes on! I know a lot more people who have one or more of these contraindications than I know who are ideal candidates for disc replacement.

I am a very experienced surgeon, and when I think a spinal operation is technically difficult, it truly is. And I think artificial disc replacement is a technically difficult operation. Every experienced spinal surgeon I talk to thinks so also. If the artificial disc is not perfectly placed, there is a high probability that it will migrate out of position. If it settles into the adjacent vertebral bodies, it will prevent any motion between them. If it migrates backward into the spinal canal it can cause leg pain or nerve damage. Conversely, if it migrates forward it can damage the adjacent blood vessels. Exact positioning of an artificial disc requires very clear live x-rays (fluoroscopy). The big problem is that it is almost impossible to obtain clear x-ray images in the operating room if the patient weighs too much. It is also difficult to safely expose the disc to replace it in a heavy individual because the wound is so deep, and excessive fat limits the exposure of the disc. To replace a disc in the low back requires that the major arteries carrying blood to your legs and the veins that carry the blood back to your heart must be moved aside (aorta, iliac arteries and veins, and vena cava). In the process of retracting these vessels aside to expose the disc they can be torn or otherwise injured. Excessive bleeding, loss of blood supply to a leg, or blood clots to the lungs can occur. The consequences may be so severe that you could lose a leg or your life! Smokers, people with high blood pressure, older, and overweight individuals are prone to have blood vessels that are more susceptible to injury and clotting. It is for these reasons that these individuals are not good candidates for disc replacement.

Lower lumbar disc replacement in men is more challenging than in women because of a nerve that is adjacent to the discs that controls normal ejaculation during sexual intercourse. In the process of exposing the discs in the lumbar spine this nerve can be injured, resulting in the ejaculation of semen backward into the urinary bladder (retrograde ejaculation). This presents two problems: difficulty conceiving children and a loss of the normal pleasurable sensation of ejaculation. Men who are anticipating disc replacement must accept the fact that retrograde ejaculation can occur no matter how carefully the surgeon retracts the nerve. If they cannot live with the possibility of this complication, they should not have the procedure.

Careful exposure of the disc is important to avoid injury to the adjacent vessels and nerves as well as to be able to accurately place the artificial disc. The exposure is much more difficult if the patient has had previous surgery such as an appendectomy, hysterectomy, or a disc replacement. This brings me to the next problem with disc replacement surgery. If the artificial disc should migrate out of normal position, become infected, wear out, or break, it should be removed and either replaced or the resulting space fused with bone. If it is difficult to place an artificial disc in the first place, it is really difficult to take one out. The exposure is more difficult and the surrounding structures are harder to retract aside. Once the artificial disc is removed, it is more difficult to replace one properly and more difficult to perform a fusion with bone graft should that be necessary.

Given all of these possible difficulties, why even have an artificial disc? Artificial discs are used to treat chronic disabling back pain secondary to disc degeneration. An artificial disc is the only surgical alternative to spinal fusion for this condition. The theoretical advantage of an artificial disc is that it preserves the motion of the disc space, thus preventing adjacent discs from prematurely breaking down. This has not been proven yet. In a U.S. FDA-approved study, a group of patients who received an artificial disc was compared in a prospective randomized study to a group of patients who underwent an interbody fusion using a metal cage (see
Chapter 7
). The serious complication rate for both procedures was less than 5 percent, but the patients with the artificial discs were happier with their surgery and had better pain relief than the patients who were fused with the metal cages. I think this study would have been more convincing if the artificial disc was compared to a group of patients who performed an intensive exercise program. Remember the study I quoted in
Chapter 9
, in which patients with chronic discogenic back pain had a satisfactory outcome from intensive back exercises? If intensive exercise works just as well as artificial disc or metal cage fusions, why take the chances of the surgical options? Remember my patient who was advised by another doctor that she was an ideal candidate for a disc replacement who exercised instead and was cured? (See her email to me on page 123)

For the rare young, otherwise healthy patient with chronic back pain from one or two degenerated lumbar discs, artificial disc replacement is a reasonable option if an intensive exercise program has not worked. But the patient must not smoke, they must be of normal weight, and must not have undergone a previous abdominal surgery.

Most of what I have said about artificial disc replacement in the low back also pertains to the neck. Since most cervical disc herniations are performed from in front and require complete removal of the disc, a spinal fusion is normally performed after removing the disc. Intuitively, it makes more sense to replace a cervical disc with an artificial disc than with a bone plug. The discs in the neck are more mobile than they are in the rest of the spine, and maintenance of this mobility may be more important than in the low back to protect adjacent levels. The U.S. FDA approved two artificial discs for the neck in 2007. There are several other artificial discs being used in clinical trials in the United States at this time. The possible complications from disc replacement in the neck are identical to those that can be encountered in an intervertebral fusion in the neck (see
Chapter 9
). The indications and contraindications to disc replacement in the neck are similar to those outlined above for the lumbar spine.

I have not personally treated any patients with an artificial disc, but I have recommended it as an alternative treatment to a few highly selected patients. After hearing a candid discussion of the pros and cons of artificial disc replacement, every patient with whom I have had this discussion has elected not to have the procedure. I think the indications for this procedure are limited in the low back to a highly selected patient, the so-called ideal candidate, whereas there is more of an indication for the procedure in the neck. Artificial disc replacement is still an “investigational procedure” in the United States. Whether this procedure will equal the efficacy of hip and knee replacement remains to be determined through refinement of the indications, technique, and long-term follow-up of the results.

It is true that heart transplants work and save people’s lives, so why can’t they transplant discs and save people’s backs? A heart transplant recipient must take immunosuppressant drugs for the remainder of their lives to prevent their body from rejecting the transplanted heart. There are a number of unwanted side effects from taking these drugs. But the risk of these side effects is better than the alternative, which is likely death. Would it be worth the risk of taking immunosuppressant drugs in order to receive a disc transplant? Probably not, but what if you didn’t have to take pills to keep you from rejecting a transplanted disc? From the extensive experience of the University of Miami Tissue Bank with transplanting major joints (to save arms and legs from amputation in cases of bone cancer) we know that immunosuppressant drugs are not necessary to prevent rejection. It seems that the controlled freezing process (the same one used to preserve live sperm and eggs) used to preserve the bone–cartilage grafts alters them in such a way that the body does not reject them the way it does for organs such as hearts and kidneys. Disc grafts are composed of a small portion of the adjacent vertebrae and the entire disc itself. This bone–disc–bone graft is controlled-frozen immediately after being retrieved from a cadaver donor. The disc grafts are similar to bone cartilage grafts in that the controlled freezing decreases the chance that they will be rejected by the body they are placed in.

The disc grafts are scanned by MRI to determine that they are normal and do not have degenerative changes. When they are transplanted, the vertebral bone from the recipient heals to the bone on the grafted disc, thus re-establishing pathways of nutrition to the graft. During this healing process, the grafted disc is in jeopardy of starving from poor nutrition. This may result in rapid degeneration of the otherwise healthy grafted disc. For this reason, transplantation of large discs (lumbar spine) may be less likely to succeed than smaller discs (cervical spine). The smaller the disc, the more easily nutrients can penetrate and keep the cells alive while new pathways are being established. Small animal studies have demonstrated that it is possible to transplant small discs that continue to function normally. But will this work in humans with relatively larger discs? A group of patients in Hong Kong who have received cervical spine disc transplants were regularly monitored for up to four years. They have had relief of pain, maintenance of disc space height, and normal neck motion. There have been no other reports of successful disc transplants in the low back.

Even if disc transplantation techniques eventually become better than artificial disc replacement, the surgery for the two procedures is equally demanding and risky. Either approach has specific risks, such as wear and breakage of an artificial disc or premature breakdown and rejection of a transplanted disc. Investigation of disc transplantation is still in its infancy, so only time will tell if it is a reasonable approach to the treatment of painful degenerative disc disease.

Good question. Genetically engineered bone-stimulating proteins (see BMP, page 96) are already available to stimulate fracture healing and spinal fusion. These are situations that require a stimulus of a specific cell function (bone production) for a short period of time (until the fracture heals or the bone fusion occurs).