Low Back Spinal Fusion vs an Artificial Disc Implant
An Interview with Jack Zigler, MD
SpineUniverse: How does a lumbar fusion compare to or differ from a lumbar artificial disc procedure?
The procedure itself is very similar, and our surgical approach is the same. We remove the disc that is determined to be the pain-generator. Then, the empty disc space is filled.
- In a fusion procedure, we implant bone material (eg, autograft [patient’s own bone], allograft [donor bone]) or a metal or plastic device (eg, interbody cage) into the empty disc space.
Additionally, there are many different materials that can be used to fill the structural component within the disc space. We may use a biologic agent, such as autograft, bone marrow aspirate, stem cells, or synthetic protein to stimulate the patient’s own bone cells to grow into, across, and around the implant. Bony growth eventually locks (stabilizes) the segment. Stabilizing the segment usually relieves pain too.
- For artificial disc implantation, we prepare the disc space to allow motion at the affected vertebral segment. After implantation, the artificial disc controls the motion. We know that patients who retain motion at a segment recover quicker, and have less break-down at the adjacent level.
SpineUniverse: What types of lumbar disorders may be appropriate for treatment using an artificial disc?
It was really designed for people who have mechanical low back pain. This type of pain often develops because the disc’s function as a shock absorber becomes poor. Age-related biochemical changes can contribute to physical alternations in a disc, such as cracks or tears. Typically, patients with mechanical lower back pain experience aching pain that interferes with their ability to participate in and enjoy life.
An artificial disc is not for people with a herniated disc that compresses a nerve root and/or causes sciatica. In those cases, if conservative treatment fails, the treatment is the surgical removal of the herniated fragment—removing the pressure off the nerve—called decompression.
Being a Sherlock Holmes is part of being a good spine surgeon. You have to be able to exclude other sources pain, such as the facet joints or ligaments, and determine whether the disc is the pain generator and is internally damaged. A disc that is internally damaged has a very limited potential to heal because the interior of the disc doesn’t have a blood supply essential to the process of healing.
SpineUniverse: Is there specific selection or exclusion criteria that we haven’t discussed?
In general, patients with osteoporosis, disc space infection or other active infection, a spinal fracture at the level that did not heal correctly, spinal tumor, or vertebral body cyst are not candidates for disc replacement. These conditions alter the vertebral body’s strength, and do not provide adequate support for an artificial disc.
SpineUniverse: What are the potential risks of lumbar artificial disc replacement?
The risks are similar to those of an anterior lumbar fusion procedure; the major risks are approach- or access-related. The approach used is the retroperitoneal approach (abdominal cavity). The same approach is used for anterior lumbar fusion or artificial disc replacement, with the caveat that for artificial disc implantation surgery, straight anterior [from the front] access to the spine is needed.
Most surgeons in the United States operate with an “access surgeon,” who is a general surgeon or vascular surgeon who provides access to the spine. This “tandem-team” surgical approach is best because the access surgeon is highly trained to work within the retroperitoneum (abdominal cavity), and to mobilize and repair blood vessels if needed. Furthermore, the access surgeon closes up the patient. Patients simply receive better care with a tandem-team.
SpineUniverse: Is the procedure performed as an open or minimally invasive surgery?
It’s a compromise between the two. The standard technique for artificial disc surgery is called a mini retroperitoneal approach. So, it’s a relatively small incision that does not cut any muscles. The incision follows the body’s natural planes all the way back to the spine. In a thin person, a lumbar artificial disc can be implanted through an incision that is no longer than about 2.5 inches in length. However, if the patient is large, a longer incision is necessary.
SpineUniverse: Please tell us how an artificial disc is implanted.
The ProDisc has a keel—a little central fin—on both the superior (upper) and inferior (lower) metal endplate. After the disc space is prepared, we cut a narrow slot in the vertebral bone above and below the disc space. The keel is gently implanted into the slots, called a friction fit that holds the artificial disc in place. Furthermore, the artificial disc manufacturer prepared the disc’s endplates using a titanium plasma spray to create bone-like pores into which new bone grows during the next 6-12 weeks.