Cervical spine surgery for the most part has yielded outstanding results. Not so with lumbar surgery, says Adam Kremer, M.D., a neurosurgeon who specializes in minimally invasive spine surgery. Dr. Kremer, a member of McLaren Central Michigan’s medical staff, has been on a 24-year quest to replicate the success of cervical surgery—in the lumbar spine.
“Most spine surgeons like working on cervical spine problems because they typically involve a ‘cleaner’ diagnosis and very successful treatment outcomes. Lumbar surgeries, however, are complicated with difficult recoveries and sometimes, less than optimal outcomes.”
But then Dr. Kremer discovered a product by Austin, Texas-based Wenzel Spine—VariLift®-LX—the only posterior stand-alone expandable lumbar interbody fusion device cleared by the FDA for one or two levels, PLIF or TLIF, with or without supplemental fixation, and intended for use with autograft and/or allograft.
Dr. Kremer, a firm believer that surgeons should aim for a more “natural” repair in the OR, said, “Traditional back surgery tends to make a weak joint weaker as it involves removal of bone and disc material without any repair. The root cause of the pathology is not addressed. Pain may persist, the pathology may reoccur, the deformity may worsen. For years, the alternative was adding a lumbar fusion via an open, midline approach. Unlike in cervical spine surgery where the disc space is accessed easily and the pathology is well visualized from an approach through the front of the neck, traditional lumbar fusion surgery through the back of the spine requires aggressive decompressions in order to access the disc in front of the nerves in the front of the spine. Because of such aggressive bony removal, pedicle screws and rods are required to internally cast the spine in hopes of creating new bone growth across the much larger disc space. Additional muscle dissection is required to place the screws and rods. Also, traditional lumbar fusion with pedicle screws and rods changes how the weight is distributed. A much greater amount of the spinal load is now unnaturally distributed through the screws and rods in the back, an area that is not designed to carry that much load. This may result in increased back pain as well as greater stressors on the spinal segments next to the fused area.”
Prior to 2008, Dr. Kremer had to rely on existing minimally invasive TLIF options. “Accessing the disc through a tubular approach and microscope meant I could achieve fusion with less tissue trauma and less deconstruction of the stabilizing structures of the spine. An interbody graft enabled me to increase the success of bony fusion in the front of the spine, analogous to cervical fusion. TLIF still required pedicle screws and rods due to facet joint removal. Though some of the load could be shared across the interbody graft in the disc space, stress shielding and loading of the back of the spine still occurred…but it was the best available option at the time. A couple of years later an expandable cage enabled me to improve spinal alignment and restore weight distribution more naturally. Moreover, it became clearer to me that bony incorporation of a porous titanium implant may be sufficient versus waiting for bone to bridge the entirety of a relatively ischemic disc space. The morbidity of lumbar fusion surgery was now significantly lower.”
And now when he would encounter a patient with a ruptured disc and unstable spinal segment he thought, ‘Do I want to do a traditional microdiscectomy and resect the disc rupture and risk making a weak joint weaker or should I remove all of the damaged disc and restore disc space height and alignment and stabilize the spinal segment?’ With a less morbid and more successful interbody fusion option, this question became more and more troublesome.
His light bulb moment
“I asked myself, ‘Why can’t I do an ACDF on the back?’ Through a tubular, microscopic approach, I now am able to access a lumbar disc without sacrificing the integrity of the stabilizing spinal segments.” Unlike an anterior approach through the neck, an anterior approach to the lumbar spine does not allow good visualization of the pathology. But a traditional approach through the back to access a lumbar disc well enough to do an interbody fusion enabled visualization of the pathology, but was often destabilizing. Therefore, pedicle screws and rods were required. Now, with the VariLift implant, I had the benefits of both approaches: direct visualization and treatment of pathology and avoidance of iatrogenic instability. Perhaps a stand-alone implant in the disc in the lumbar spine could achieve similar great results to ACDF.
“Ultimately,” says Dr. Kremer, “placing screws and rods requires a lot more muscle dissection and the potential for muscle injury, resulting in additional pain and disability.” Necrotic muscle increases the risks of infection. Moreover, the additional OR time, bulky equipment encroaching on the sterile field and staff, radiation, and increased blood loss add to risks of infection. I also have noted that even under the best of circumstances, it is difficult to place pedicle screws without interfering with the adjacent facet joints. It is conceivable that the pedicle screws directly abutting mobile facets could increase the likelihood of adjacent segment disease and pain. Also, he worries that the addition of rigid metal implants converts a lot of the weight distribution to the back of the spine and warns, This is not how it is supposed to be. This increased load on the back of the spine may serve to accelerate adjacent segment disease, contribute to additional muscle fatigue and pain, and off-loads the front of the spine where fusion is desired. Ideally, the weight would be redistributed to the front of the spine which would enhance bony fusion.
Then VariLift®-LX, a unique stand-alone fusion option for the lumbar spine, came along and quickly impressed Dr. Kremer. He believes the device is opening a world of opportunity for spine surgeons. “With this stand-alone device, I am able to access the spine through a round tube with a microscope, access the impinging pathology directly, remove the offending pathology under direct visualization, remove the degenerated disc completely, place an implant safely via the same trajectory, expand in-situ, restore disc space height, as well as restore alignment and proper weight distribution. I am strengthening, adding, restoring—it’s a brilliant design.”
Added bonus…enhanced healing
Being able to do all of this through a 3cm transverse incision is “remarkable.” Dr. Kremer: “These are not vertical incisions…they follow Langer’s lines so that ultimately means enhanced healing. This can be particularly important for patients as sometimes they associate the quality of the surgery with the aesthetics of the results.”
The procedure is much more rapid as there are no wasted steps, and less steps overall. The surgery does not require nearly as much muscle or bony removal to get to the pathology. Because only one C-Arm fluoroscope is required, the sterile environment is much safer. Not wearing lead means less surgeon fatigue. The vastly reduced morbidity means the procedure is outpatient. This is a much easier sell to patients in the middle of a pandemic! An outpatient fusion, without screws and rods - an ACDF on the back.
“VariLift®-LX is ideal as it has four large fenestrations enabling bony ingrowth. As a porous titanium implant, it enables osteointegration. Traditional fusion relies on bone bridging the entirety of the disc space, essentially a large air gap. This is very challenging and slow process given the relatively barren environment of the disc space, even with supplemental rigid screw and rod fixation. The scaffolding created by a titanium interbody implant like VariLift may enable bony incorporation to occur in a much more timely fashion as the implant is directly opposed to the endplates. Because its placement does not require facetectomy, it does not require additional posterior fixation: no screws or rods. This avoids stress shielding of the interbody implant which also serves to speed bony incorporation.
“VariLift®-LX allows you to switch gears mid-procedure,” says Dr. Kremer. In the event that the intraoperative feedback is such that fusion is not required, the implant does not need to be placed as the spinal segment has not been deconstructed, you are not pot committed. This is very much unlike traditional fusion where screws may be placed at the outset of the procedure or extensive decompression to get to the pathology necessitates fusion. If the intraoperative feedback is worrisome for poor bone quality or subsidence is a concern after endplate preparation, screws and rods may be added. If a transforaminal approach fails to adequately address medial pathology, a separate more medial approach and laminotomy may be added.
When to use
VariLift®-LX offers the broadest clearance on the market, says the company.
“Although I now use VariLift®-LX in a large portion of my TLIF cases, I did have to develop confidence. I was an early adopter of stand-alone cervical implants. To my surprise, I saw improved outcomes with less symptomatic cases of pseudoarthrosis. The avoidance of tying multiple levels together with a long, proud plate seemed to help avoid adjacent segment disease as well. The issue of potential subsidence given the large surface area of a lumbar interspace still gave me pause. My initial foray into expandable interbody implants occurred with RISE. I was worried about potential endplate fractures, knowing how painful these are to patients. To my surprise, patients who underwent MIS-TLIF with RISE and screws and rods did very well, better than patients with static PEEK implants with screws and rods (published data, AK journal of spine surgery). It occurred to me that bony incorporation of a porous titanium implant may be sufficient, versus complete bridging of bone. It was obvious that the majority of elderly patients with degenerative spine disease were able to achieve stability in spite of complete facetectomy and discectomy and often aggressive bilateral decompressions, well before complete bony fusion was evident radiographically. Could the same results be obtained if limited facetectomies were performed and only an expandable interbody implant was placed. Would osteointegration occur fast enough, before subsidence and collapse would occur? With the FDA approval of VariLift and my experience in the cervical spine suggesting this was indeed possible, I began to offer this to patients with severe foraminal stenosis and dynamic foraminal instability. The success was immediately obvious. It has now become an important tool in the bag. While I almost always used to rely on BMP allograft for MIS fusions, I have found DBM allograft sufficient for bony incorporation. The reduced cost profile has been a big win. The tubular nature of the entire surgery, has made if a very effective option for my obese patients, in whom xray visualization and placement of screws would otherwise be challenging.
A grooved and fluted device, VariLift®-LX offers surgeons bony contact with the endplates and a generous graft chamber that allows for better aid in fusion.
Dr. Kremer: “This device is a titanium implant. Both calcium and titanium are metal ions, and we find that the body treats titanium like calcium. My goal is for the bone to grab onto the metal implant…and I’m seeing that. My patients are reporting dramatic improvements in pain at five weeks and are able to do vigorous physical activity by 8 weeks. While even traditional lumbar surgery has been effective at alleviating radiculopathy, most patients still report a certain amount of back pain. But now, I am seeing VAS back scores of ‘0’ out of ‘10’ at 6 weeks. This is truly special. Referral patterns have rapidly changed. The intraoperative photos under the microscope demonstrating complete decompression, and x-rays demonstrating pretty alignment are nice souvenirs for the patients too.