561- How Cervical Fusion Impacts Adjacent Segment Disease

Welcome to The Evidence-Based Chiropractor, where each week we deliver the latest chiropractic research and marketing strategies, all in the time it takes to get to your office. Now here's your host, Dr. Jeff Langmaid.

Hello and welcome to The Evidence-Based Chiropractor. I'm your host, Dr. Jeff Langmaid. On today's episode, we're talking all about cervical fusion adjacent segment disease challenge and what actually happens to the rest of the cervical spine. Brand new study. We'll dive into it momentarily. Before we get started, big shout out to a few of our partners. Care Plan Pro, whether you are selling care plans, memberships, concierge, and I view a care plan as anything more than one visit at a time. That is a care plan. doesn't mean it has to go all the way to 27 years on the first visit, but everybody has a different way of practicing. So no matter how you practice, if you want to get off of writing down care plans on paper and feeling like you're selling timeshares, head over to careplanpro.ai. I'll drop that link down below, as well as Leander Tables. You can save $750 using the code EBC off their 2026, off of their Series 950 table, flexion distraction table. Fantastic. And Shockwave Centers of America, $500 off And a free cart. Connect with those partner sponsors. Let them know that you found out about them on this podcast and save big. But as I said at the top, today we are talking research. And really the question was, when you fuse part of the cervical spine, what happens to everything else around it? Mechanically, that's probably pretty obvious. If you take one or more segments and lock them down, The rest of the cervical spine has to do more work, right? Because the patient's still going to look down at their phone. They're going to turn their head while driving. They're going to look over their shoulder. So where does all that motion go? Does the segment directly above the fusion start moving more? Does the segment below compensate? Does the whole cervical spine redistribute that motion? And more importantly, does that mechanical compensation help explain when some patients eventually develop—

Pain.

What we call adjacent segment disease. Well, that's exactly what the researchers were looking at. This is a 2026 study titled The Effect of Single-Level and Multi-Level Cervical Fusion on Adjacent Segment Motion. It's a biomechanical analysis. Again, we'll drop that link down in the show notes. And there was a really interesting headline from this paper that a single-level fusion did not significantly increase motion at the adjacent segments.

Oh.

Motion's different than load. But as the fusion got longer, especially when they fused 3 levels, the biomechanics of the remaining cervical spine untouched changed a lot. And some of that compensation didn't occur immediately next to the fusion. It occurred several levels away. And that's probably the most interesting part of this study to me is how adaptable our bodies are. Now, I wanna be super clear on my stance of this right at the beginning. Which is anytime you want to do everything you can to not fuse the spine. I mean, this is a last-ditch effort type of thing. Obviously, there are occasionally red flags where it's absolutely necessary, myelomalacia, et cetera. But really, this is something where you want to avoid this at all costs. The load and stress— I mean, sometimes these studies, I feel like, downplay adjacent segment disease. That's a very real thing. And I saw in multiple orthopedic groups that I practiced in, As soon as that— it was like a pent-up demand. As soon as one-level fusion happened, it could take 5, 10 years to get there after the person thought they might need it, and they were back for a second, third level very, very quickly. It was once that dam breaks, it is really hard to come back from. So that's really important. And I think a lot of times patients feel— I heard this all the time— well, I just want to fix the problem. And it's like it's partially fixing the problem. I mean, if the problem is I hope to get rid of a good portion of pain that is on— I can't get rid of any other way. You got a decent shot. But this is very rarely a, well, I permanently fixed the problem and all my pain went away. That happened so infrequently, especially when we get into fusion, multilevel fusion. I could probably literally count on the number of my hands And I saw 10,000, 20,000 total patients over the years in those orthopedic groups via imaging review, pre-surgical consult, post-surgical consult. So this is something that's really, really serious. And I think us as chiropractors need to step up and lean in to be able to guide and direct our patients. It doesn't mean say, hey, never do that. That's the worst thing you could ever do. It means actually having a real conversation where if somebody thinks, well, I'm too far gone for chiropractic. This is going to fix my problem. There is multiple problems in that statement, and being able to address them not in a defensive way, but in a really helpful, guide-based, proactive way, really, really important because cervical fusion is not a rare procedure. Over 180,000 cervical fusions are performed every year just in the United States with ACDF, anterior cervical discectomy and fusion. That's through the front, of course, making up a majority of those procedures. And generally speaking, you know, outcomes can be okay. You know, the paper's not saying fusion doesn't work. It's really analyzing what happens afterwards, specifically that adjacent segment disease. So they cite that adjacent segment disease occurs approximately 3% per year. And that's important because that's compounding over time. When I first read the 3%, I'm like, that is a—

Yeah.

I mean, 3%, this is like 97% of the time it happens, not 3%, but it's 3% per year. So they kind of say, well, we don't really understand why it happens. I think it's pretty obvious, but there are 2 buckets that this fits in, right? The natural progression of the original degeneration. Somebody who had enough cervical degenerative change to require surgery at 5, 6 probably is just predisposed and already in progress To having degeneration at 4-5 and 6-7. Or, and/or I would say, the fusion itself changes the biomechanics. So you eliminate motion at one portion of the cervical spine, the other segments have to compensate, and they experience greater motion or loading. And over time, that contributes to advanced degeneration. And the reality is probably a combination of this and more. And that to me is really the important component. Is that anytime we try to take some— this is a complex thing, right? Somebody has a real problem, which is why they're having a fusion, which is a real surgery. And then they're coming out afterward and living a dynamic life. Often things like this are multifactorial. So in this case, this was a laboratory biomechanics study. So they used 9 cervical spine specimens extending from C2 to T2. Average was 49 years old, range 30 to 67.

Wow.

And they screened out specimens with advanced degenerative changes. So they were looking at relatively healthy cervical spines from a structural standpoint rather than like severe spondylitic type specimens. So they created 4 different fusion configurations, 5-6, which represented a single-level fusion, 4 through 6, 2-level of course, and 5 through 7, 2-level, and finally 4 through 7, C4 through C7.

Okay.

A 3-level fusion. They tested the spines in flexion, extension, left and right lateral bending, and left and right axial rotation. So it wasn't somebody manually pulling on a cadaver neck. They actually used robotics basically to, with force, a force moment sensor and 3D tracking to really allow what they call displacement-controlled testing. So instead of applying the exact same force and seeing how far the spine moved, They told the spine, we want you to move this far. Then they tested at 30 degrees flexion, 20 degrees extension, plus or minus 25 degrees rotation and lateral bend. And they measured how much force or torque it took to get there. And then how the individual segments shared that motion. So I think this is a pretty novel and pretty cool way to look at, well, what's going on? So before looking at the fusions, the researchers measured Where motion naturally occurred. Good idea. In a cervical spine. In flexion, most of the motion occurred at 3-4, 4-5, and 5-6. In lateral bend, 2-3 and 3-4. And axial rotation had uneven distribution across many cervical levels. So before fusion even enters the picture, the cervical spine is not behaving like 6 identical hinges stacked on top of each other, right? Different segments, as you know, contribute Differently depending upon the movement. And then you get into complex movements, whole nother story. So this helps start to explain why compensations after fusion aren't always located exactly where you might predict. So one of the big results was when the researchers fused 5-6 alone, they successfully reduced motion at the fused segment. So in flexion, for example, 5-6 motion dropped by approximately 6 degrees compared with an intact spine. And statistically, that's highly significant. So there was no statistically significant increase in motion at the adjacent segments or anywhere else in this study. So when you fuse 5-6, it doesn't necessarily mean immediately the adjacent segments move more. Now, motion is different than load, and that is really important to keep in mind. But when they extended that another level, so for, let's say, a C4 through C6 fusion, During flexion, motion at 2-3 increased by 2.5 degrees. And that's interesting. 2-3 is not immediately adjacent to that fusion level. The segment immediately above, 4 through 6, is 3-4. Yet the statistically significant compensation showed up a level farther away. So compensatory movement doesn't necessarily stay next door to the fusion. How do you apply this in practice? Why does this matter? Well, Don't always become myopic. Always check out the levels above and below. I know my rule of thumb learning in school was always, well, you typically adjust the levels adjacent to. Maybe you do, but don't forget about the fact that it can impact the body region, not just the level adjacent to. So don't become myopic with always just looking above or below the fusion site and really Take the holistic approach at looking at the entire body region. And of course, anytime you're analyzing a body region, look at the next body region adjacent to it as well as my recommendation goes. So when they did a 5 through 7 fusion, slightly different pattern. 2, 3 was nearly 4 degrees of increase, 4, 5 almost 3 degrees. So you're seeing it both locally and remotely.

Uh-huh.

And then the, uh, the 3-level fusions, C4 through C7. They eliminated motion at 4-5, 5-6, 6-7, of course. That's when the cervical spine started behaving a lot differently. The 3-level fusion produced the greatest changes in adjacent and non-adjacent segment. So during flexion, 2-3 increased by almost 3.5 degrees. Extension, 2-3, 3-4, big increases there. Right axial rotation, 2, 3 big increases there. There were just a lot of increases across the board. And I think that tells a really interesting story as well, which makes a lot of sense. A 1-level fusion, our bodies are really good at being able to compensate, work around things, right? It's how we're built. And a fusion is no exception to that. But once it starts becoming extreme limitations of matter, right? There's, you know, C1 through C7. So you start fusing 3 of those levels, you're taking out a lot of motion. Different things start happening, right? Big changes start happening. And they looked at torque, remember? And as the fusion became longer, it took more force to get there. So, you know, and a lot more force. The more levels that were fused, the more force it took. Well, in somebody that's deconditioned, Probably in most cases, most of the time, by definition, if they're having a fusion, they're probably, you know, again, in rare cases, they're probably in great condition. In most cases, most of the time, they're probably pretty deconditioned to begin with. So now you're requiring more force, more torque by the person's muscles, obviously, to be able to get normal, quote unquote, normal range of motion, which is of course not normal and compensatory on the adjacent levels. This is where I start to think about, wow, that is where a degenerative cascade can occur. Because in many of these instances, again, the levels below and above in most cases are not perfect to begin with. So you're taking compromised levels, fusing the worst of them, the problem, if the doctor can find it, hopefully correcting the issue, whatever that issue is, But you're gonna pay the piper down the road. And different people have a different amount of tolerance. Some people, you know, it might be a very short amount of time. I've seen mere months go by and adjacent levels fall apart. I also have seen individuals where they had fusions decades ago and the adjacent levels look pretty good and they end up with an isolated problem, you know, 4 levels away. This is where it's just, as days become weeks become months become years, time and gravity ultimately remain undefeated. But there's a lot of variability in that. So to me, the most important part about this study was really highlighting the fact that, you know, A plus B plus— it does not always equal C when we're looking at spinal fusions. The larger the fusion, the weirder things can happen. You know, you start to see really bizarre and really, what I'll say is asymmetrical compensation patterns. On a single-level fusion, hey, most people can probably, quote unquote, get away with that from a biomechanical standpoint. But the torque is still going to increase, load is still going to increase, and it doesn't always happen at the direct level adjacent. You have to look beyond that. So I loved this study because I think it really points out important things that all of us can look at. We probably all see people that have had fusions, and we probably all see people that have been told they need a fusion. Many of those individuals come into us to avoid it, and anything we can do to be able to build up our tools, to be able to build up our skill set, and ultimately help them avoid that is a really good idea. But there's still going to be a fractional percent of people who do go through with the fusion, and some of those individuals with multi-level. And some of them, again, they had it decades ago. They're walking into your practice. You didn't have a chance to take care of them before, but you have an opportunity to take care of them now. So always look at the adjacent levels and beyond, and do not forget that there is both biomechanical range of motion changes and load changes, and both are interacting constantly. in real time with your patients. Before we wrap up today's episode, big shout out to the RehabFix Hybrid Program. If you're looking to generate more revenue beyond the 4 walls of your practice, I don't think there's a better program out there. Grant's done it himself. He's helped many other doctors. We'll drop a link down below if you are interested in building in. It doesn't mean you have to abandon your brick and mortar, but adding onto that brick and mortar and reducing that trade of time for money. The RehabFix Hybrid Program, fantastic way to do it, as well as the NovoPulse OA Recovery Program. You can bring in OA recovery program, including the NovoPulse device, into your practice with no out-of-pocket expense, no capital expenditure. Uh, fantastic program, fantastic device, 6 patents, FDA listed. If you have not checked out NovoPulse, you are missing out, but you don't need to. You can just click on down below. Thank you so much for tuning into this podcast. If you have not left a rating or review, I would love it if you would take a moment and do so. I hope you have a fantastic week in practice, and I will talk to you soon. Bye.

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