Lytic spondylolithesis typically occurs after a stress fracture has divided the pars interarticularis. These stress fractures, which often occur in late adolescence or early adulthood, disconnect the vertebral body and pedicles anteriorly from the laminae and spinous processes posteriorly (Fig. 1). This disconnection bypasses the hooking mechanism of the facets. Over time, shear stress through the disk and longitudinal ligaments allows spondylolisthesis to occur. Degenerative spondylolisthesis, on the other hand, results from direct degenerative destruction of the facet joints of the spine leading to lumbar or lumbosacral instability, with or without stenosis.
Speaking at the Federation of Spine Associations Specialty Day program, David A. Wong, MD, MSc, and P. Justin Tortolani, MD, debated whether minimally invasive surgery (MIS) or open surgery would be the better option for a patient who has a long history of symptoms consistent with lytic spondylolisthesis, after multiple attempts at nonsurgical treatment have been unsuccessful.
MIS is a “great option”
Although a minimally invasive approach has more often been applied to degenerative spondylolisthesis, MIS can be a viable option in lytic spondylolisthesis, said Dr. Wong, with the caveat that the surgeon must be very careful about patient selection.
“The principle of MIS is to minimize the soft-tissue trauma, get a good clinical outcome, and minimize complications,” Dr. Wong explained. “In general terms, MIS is a great procedure.”
Dr. Wong pointed out that degree of instability marks the initial difference between lytic and degenerative spondylolisthesis.
“I believe it’s critical to look at the degree of stenosis in the foramen,” he said, “where the residual pedicle of L5 butts against those loose posterior elements. Over time, you get what I call a ‘mushroom-cap osteophyte.’ In my opinion, that’s the reason Gill laminectomies fail in many situations. The surgeon has to make sure that the lateral recess stenosis off that mushroom-cap osteophyte is decompressed.
“Depending on the radiographic findings, a surgeon must be very careful in deciding whether to take the MIS approach,” he emphasized.
Dr. Wong explained that good data support the use of MIS as an alternative to open surgery for lytic spondylolisthesis. One retrospective study compared 66 patients who were treated with either MIS or open surgery; similar clinical outcomes and fusion rates were reported for both procedures.
A meta-analysis of 34 studies—four of which were randomized, controlled trials (RCTs)—found that clinical outcomes trended down with a laminectomy.
“What that means to me,” he said, “is that in many cases an indirect decompression—one of the things you do in an MIS approach—is adequate. The key point is to look at the analysis of the pathology, particularly the stenosis.”
Finally, Dr. Wong pointed to an RCT of 50 patients that compared posterolateral and interbody approaches. The results of this study indicated that the interbody approach was associated with improved outcomes in terms of fusion rates and angulation.
“Interbody is how you do an MIS,” he noted.
Dr. Wong wrapped up his presentation with a few notes on the use of bone morphogenetic protein (BMP) in MIS. Although autografts are generally used at his institution, some patients have been referred from other surgeons. He has come across at least one case in which BMP was linked to ectopic bone in the spinal canal.
“Be careful,” he cautioned. “BMP is used a lot for MIS transforaminal lumbar interbody fusions (TLIF) and for posterior lumbar interbody fusions. Some techniques—such as using a single sponge anterior and three barriers behind the spine—can be used to minimize the risk.
“So, for lytic spondylolisthesis, is MIS still a great option? Absolutely. But keep an eye on the sagittal alignment, analyze the stenosis, and be careful with the BMP,” he concluded.
The “gold standard?”
Speaking in favor of open surgery, Dr. Tortolani noted that the goals are the same: quality outcomes, great decompression, and a stabilized, fused spine.
“We may or may not want to do interbodies for various reasons,” he said. “But this is where we differ, and it goes back to what we learned in medical school with Occam’s razor: the simplest solution to any given problem is the best solution.”
Dr. Tortolani noted that all surgeons are challenged with the value paradigm of outcomes over cost.
“Either we have to improve our outcomes and thereby increase our value, or we need to decrease our costs,” he explained. “And the best research we have to date finds excellent improvement in health-related quality of life for degenerative spondylolisthesis treated with decompression and standard posterior screw instrumentation. It’s comparable to the gold standard of total hip replacement.
“As for lifetime incremental cost utility, the same research shows results approaching, but not quite reaching, hip and knee replacement. This is open surgery—not increasing the complexity of what we do—bread-and-butter spinal surgery.”
Dr. Tortolani pointed to an RCT that looked at cost utility with 2-year follow-up, and found that patients treated with TLIF had a greater length of stay.
“Should we be using TLIF at all?” he asked. “For degenerative spondylolisthesis, the answer is no. It’s not safer, it’s more complex, and it’s less cost-effective. And regarding MIS, can adding complexity improve outcomes?”
According to Dr. Tortolani, the evidence suggests no. Based on operating time, an open approach is favored; if blood loss is the measure, MIS is preferred. Fusion rates are similar for both procedures. However, he noted, the best studies so far offer only level 2 evidence.
“There is no level 1 data,” he admitted, “so the studies are biased. Starting at 6 months and going out to 2 years, MIS has some perioperative improvement: shorter length of stay, less blood loss, less narcotic use.
“However, MIS implants use more pedicle screws. BMP usage is higher. Neurologic complications are higher. Radiation exposure is 3 to 10 times greater with MIS procedures than with open procedures. We’re not sure what the risks of that are, but they’re not trivial.”
Dr. Tortolani argued that the learning curve for MIS presents an ethical problem. One study looked at the first 90 MIS cases performed by a single surgeon and found that it took 44 cases to reach the asymptote.
“The patients treated during that learning period experienced worse back pain, worse leg pain, and worse neurologic scores than patients treated later. The question becomes, who are you going to expose to your learning curve?
“The best evidence supports simplicity over complexity,” concluded Dr. Tortolani. “MIS techniques have to show superiority to justify the complications associated with the learning curve and the poorer neurologic outcomes. Open surgery has three distinct advantages: better visibility, better versatility, and the fact that it’s easier to teach and learn. That suggests it should remain the gold standard.”
Disclosure information: Dr. Wong—Anulex, Allosource, United Healthcare, Denver Integrated Imaging North, Huron Shores Investments LLC, Neurotech/CervIOM, Wolters Kluwer Health—Lippincott Williams & Wilkins, The Journal of Bone and Joint Surgery—American, Neurosurgery, Orthopedics Today, Spine, The Spine Journal, International Society for the Study of the Lumbar Spine, North American Spine Society; Dr. Tortolani—Globus Medical.
Peter Pollack is electronic content specialist for AAOS Now. He can be reached at: email@example.com
- Patient selection is important in determining whether to perform MIS or open surgery for lytic spondylolisthesis.
- Current studies indicate that MIS results in shorter hospital stays and less blood loss, but open procedures take less time in the operating room and require less radiation exposure. Fusion outcomes are similar.
- MIS has a longer learning curve, which may result in poorer outcomes.