TLIF Popular Spinal Fusion Technique Has Some Major Problems
In this study, spinal surgeons from The Rothman Institute at Thomas Jefferson University Hospital in Philadelphia take a look at the transforaminal lumbar interbody fusion (TLIF) technique for spinal fusion. They focus on its safety, effectiveness, and compare complications using two different grafting techniques.
The transforaminal lumbar interbody fusion (TLIF) technique is used to avoid the problems that come with entering the spine from the front (anterior approach. Transforaminal means the surgeon gains access to the spine from the back and side. The surgeon makes a posterolateral incision and removes one of the facet (spinal) joints so the disc can be taken out.
Interbody describes how the fusion is circumferential (all the way around and from front-to-back). Once the disc is removed, the two vertebrae are distracted or pulled apart gently and a special device called an interbody spacer is slid into the disc space. The spacer helps restore normal disc height, which in turn, takes pressure off the spinal nerve roots as they leave the spinal cord and pass through the opening formed by the vertebral bones.
Bone graft (human or synthetic) is inserted in and around the disc space to complete the fusion. The patient has a choice of two kinds of human bone graft: allograft (bone from a donor bank) or autograft (bone taken from the patient's pelvis). A third choice is the use of rhBMP-2 bone substitute. rhBMP-2 stands for recombinant human bone morphogenetic protein type 2, so you can see why they shortened it to rhBMP-2. This protein stimulates the body's natural production of bone.
All of this is done to treat problems like degenerative disc disease, chronic disc herniation, and spondylolisthesis (misalignment of the vertebral bones). Back and leg pain from these conditions can be severe enough to cause disability. TLIF is one way to eliminate back pain thought to be caused by the disc.
The TLIF has some advantages over other fusion techniques, but it also has some potential problems. The authors of this study are trying to determine how safe the procedure is and whether or not it is effective. The patients in the study were all adults between the ages of 18 and 80. They had a wide range of back problems including degenerative disc disease and/or herniated disc(s), degenerative spondylolisthesis, and previous (failed) lumbar fusion.
Each patient had a single-level TLIF. Some had an autograft, while others were treated with rhBMP-2. Half of the patients who received the bone substitute were also treated with Duraseal, a water tight sealant that keeps the bone substitute from leaking into the spinal canal or around the nerve roots where it could act as an irritant. Without the Duraseal, there is also a risk of bone formation in the spinal canal, which could put pressure on the spinal cord causing pain and dysfunction.
Comparisons were made between the two groups using several measures. Postoperative pain (at the fusion site and at the donor site for those who had an autograft) was the first outcome measured. Patients were interviewed over the phone asking about their pain levels. X-rays and CT scans were taken to show results of the fusion. And the medical records were reviewed looking for reports of any complications.
Previous studies have reported up to a 35 per cent complication rate using the bone substitute. Complications include screws coming loose or placed in the wrong position, interbody cage movement called migration, and infection. Sometimes pockets of blood form called hematomas or too much bone forms, a condition called heterotopic ossification. There can also be enough disturbance in the area of the spinal nerves that results in persistent nerve pain.
After all the information was in and the data was analyzed, here's what they found. First, regarding pain: one-third of the patients who had bone taken from the pelvis reported continued pain at the donor site. Leg pain from nerve irritation called radiculitis was a common complication affecting 10 per cent all patients. Those who had the rhBMP-2 reported radiculitis more often than the autograft bone fusion. That was not surprising because other studies have reported the same thing. It's likely that the body responds to the rhBMP-2 as a foreign agent and sets up an inflammatory response.
There were other reasons for the radiculitis. In some patients, there was excess bone formation around the fusion site that extended as far as the opening for the nerve. Bone formation in the spinal canal and around the opening for the exiting spinal nerve root narrows the space for the nerve and compresses (pinches) it. Pressure on the nerve or irritation of the nerve can set up a pain response that may or may not go away when the pressure is removed. One patient had an infection, another a malpositioned screw. But the most significant finding was that patients who did not have the Duraseal were four times more likely to develop radiculitis compared with those who had the Duraseal.
Taking a look at the fusion rates, they found similar rates of nonfusion (around three per cent) between the two groups. The 97 per cent who had successful fusion demonstrates the success of the TLIF procedure. The biggest problem still remains donor site pain for anyone having an autograft. But the authors point out one important finding. The donor site in this study was along the posterior (back) portion of the pelvic bone. The incision for the donor site wasn't that far from the incision for the lumbar fusion. It's possible that the combination of pain from both incision sites could have made it seem worse than it really was. They believe this factor bears further study and analysis.
The suspicion that rhBMP-2 would cause a high rate of complications was indeed true. The biggest problem as mentioned was the extra bone growth. What can be done about this? Well, surgeons are trying different things. It's not clear what is causing the problem. It could be that bleeding when the disc is removed might be a factor. Moving the sponge with the rhBMP on it and the interbody spacer forward (away from the spinal canal, incision site, and area of bleeding) might help. This is another area where further study is needed.
In the end, the authors felt that TLIF has equal complications no matter which way it's done. But at least with rhBMP-2, there are no additional problems from donor-site pain, infection, and bleeding. On the other hand, the bone substitute seems to set up extra bone growth formation that causes painful radiculitis. Whether or not one is better than the other remains to be seen. Perhaps long-term follow-up will add some helpful information to make that determination. Stay tuned!
Jeffrey A. Rihn, MD, et al. Complications Associated with Single-Level Transforaminal Lumbar Interbody Fusion. In The Spine Journal. August 2009. Vol. 9. No. 8. Pp. 623-629.