Risk Factors of Arthrogenic Muscle Inhibition - #AMR385

We’ve all seen it: the acute ACL patient who drags their leg into the clinic, unable to squeeze their quad to save their life. We call it Arthrogenic Muscle Inhibition (AMI), and for years, we’ve treated it as a stubborn, long-term enemy. But a fascinating new study from the American Journal of Sports Medicine suggests we might be overcomplicating it.

Researchers analyzed 300 acute ACL patients and found that while AMI is incredibly common (affecting over half of patients), it’s also surprisingly fragile. In fact, they found that nearly 80% of cases could be fully reversed in a single session with simple exercises. In this episode, we dive into the 'Red Flags' that predict quad shutdown—including one common sleeping habit you need to ban immediately—and how to flip the switch back on for your patients.

To see full show notes and more, head to: https://mikereinold.com/risk-factors-of-arthrogenic-muscle-inhibition

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Transcript

Cold Open And Topic Preview

SPEAKER_00 0:00

On this episode of the Ask Mycronophil, we talked about some of the risk factors behind orthogenic muscle inhibition after ACL injury. The Ask My Crino Phil. Helping people feel better. Before we get to the podcast, I wanted to make sure you knew about my free online course on the introduction to performance therapy and training. If you want to learn how to get started optimizing and enhancing performance, this is the course for you. Head to micrennel.com/slash performance to sign up today. Today we have another journal article review, and Brenda Gates is going to take the lead on this one. Um I thought this was a great article. I really like this. There's a couple cool things I thought in this, but just a quick introduction to exactly the title and everything, so I get this right, and the link will be down in the show notes. The incidence of risk factors for artrogenic muscle inhibition and acute ACL

Free Performance Therapy Course

SPEAKER_00 1:16

injuries, a cross-sectional study and analysis of associated factors. And this was published in AJSM in 2024. And if you notice in these reviews, we're trying to pick some really good influential articles that are changing our practice, but also from reputable journals. Kind of keep that in mind. So, Brendan, what'd you think of this article? What's uh what are your thoughts?

SPEAKER_03 1:38

Yeah, I really like this article. I think uh they did a really good job of explaining some things that I think we see

Paper Setup And Why It Matters

SPEAKER_03 1:44

clinically quite often, um, but quantified it really well. Um, I think before we move into a little bit more of the review, just wanted to quickly touch on what is arthrogenic muscular inhibition and try to see if I can put this together in a relatively simple way. But to my understanding, AMI or arthrogenic muscular inhibition is a protective neural response, right, to uh to a knee joint injury uh where there's altered sensory input from the knee, which then drives inhibitory signaling at both the spinal and the cortical levels, right? So brain and spinal cord. Um, and this uh shuts down the quad activation and it promotes the hamstring flexor reflex, which then in turn leads to a loss of knee extension, so a neural block rather than a mechanical or structural block. Okay. Um but as we look through this in the paper, what they kind of sought out to do is they said, you know, we know AMI is common

AMI Explained And Quad Shutdown

SPEAKER_03 2:37

after knee injury. Uh we know it's associated with quad atrophy, weakness, knee extension loss, but then other things like stiffness, problems with gait, scar tissue, and some more. Um, but what they said they didn't know was how common it actually is in clients and who is at the most risk and whether they can clinically detect and reverse it. Um so what they did is they used this new uh AMI classification system, sonary coquette AMI classification, uh, and they set out to basically see how often it occurs, how reliable the classification was, and to look at risk factors or you know, maybe better described as red flags that are associated with AMI. Um so what they did was they took 300 ACL injured patients that were within six weeks of their injury, uh, and they were evaluated at the clinic, and they were given uh they were given patient reported outcome measures, a physical exam, and then they had their AMI graded by two independent surgeons. Um, we can look through it a little bit more specifically, but in turn you know, short, the grades go from grade zero, which is the quad fires normally and the knee straightens fully, all the way to the other side of the coin, which is grade three, which is a chronic fixed loss of extension that does not resolve without surgery. And then in between those two bookends, there were four grades that were varying severities of reversible AMI. Okay. Um and so what did they find? They essentially found that out of those 300 patients, 170 of them

Study Design And AMI Grading

SPEAKER_03 4:03

presented with some severity of AMI. Um, none in the grade three level there. So these are all reversible. Um, but that's 56% of all the ACL patients that they looked at. Um out of those 170, 135 of those patients were able to reverse their AMI in just one visit. Um, using some simple exercises, they used uh some hamstring fatiguing exercises, and then followed by quad reactivation exercises, um, and they were able to combat that AMI in that first session. So 79%. Um the other 35 had to use uh other methods like biofeedback and motor imagery, things like that, using a little bit more uh time and a more structured approach. Um, but they were able to reverse it. So this

Results And One-Visit Reversal

SPEAKER_03 4:48

proved that AMI is common, but it's uh not fixed damage, uh, it's neural inhibition in these cases. Um they also found that the AMI patients had significantly worse outcome measure scores, so they felt and they functioned worse than people who did not have AMI. Uh and then they identified some risk factors or what they affectionately termed red flags, more likely, uh, that were associated with AMI. So they found that if you had swelling, if you had high reports of pain, if you used crutches, if there was a pillow under the knee, uh if it was a multi-ligamentous injury, or if the duration between when they had their injury and when they were seen for the first time were uh a short period of time, any of those, you were two to three times more likely to have AMI present. And again, these aren't causes of AMI, they're just associated with AMI likely being suspected. Um, interestingly enough, the only risk factor, quote unquote risk factor, associated with a lower risk of AMI was actually a previous HDL injury. Okay, and so that's ipsilateral or contralateral to the the investigated ACL injury that we're talking about now. And so, you know, does that suggest maybe some CNS adaptations? Maybe I'm sure we'll talk about it. Um I thought that was really interesting. Clinically, like, what do we take away from this? You know, we know AMI is likely present after an HCL injury. Um, so if you have that effusion, pain, you're using crutches, the pill under the knee, multiligamentus, that's short duration between injury and evaluation, those are all things that should say, like, hey, we probably have AMI present here, let's address it before if we move and we waste time. Um, it tells us that again, with those exercises, they they referenced the paper to combat a reverse at AMI and those 79% of clients that came in. Um, and they just used a like a PNF contract relax technique with the patient in throne, and then they did a short or quad variation to get the quad functioning. So, like very applicable to what you can do in clinic, you know, and it's it's not taking very advanced techniques, I don't think. So hopefully that's something that we can use, the listeners can use to work on that. Um the biofeedback I think is interesting. You know, I championed I I know people use the M trigger, um, and I think that that's helpful to get the quad firing that was used in those people that had the uh 35 clients that need a little bit more time to combat their AMI. Um but the other thing I think we found is that we need to stop waiting, right? So it's most common early AMI. Um it's most reversible early. Um and I I wonder if plenty you'd agree with this here, but like as soon as you get that heel pop, right, and you can do your straight leg raises and you can do uh that without a quad lag, like life gets a lot easier in HTL rehab. Like gate is easier, PT is easier, just like moving around in life becomes a whole lot easier. So I think the earlier we can address AMI, okay, and according to this, we can do it pretty easily in most cases. Um we save a lot of wasted time, wasted money, and you know, unnecessary quad atrophy that we're already gonna have. So that was a lot, tried to fit it all in there, but uh, I'll kind of let you guys talk. I think uh I have more thoughts, but we'd love to hear yours.

SPEAKER_00 7:52

Uh great summary, Brendan. That was awesome. Uh so I think some big findings here. Like I love the pillow thing, right? Like we actually have definitive evidence on having a pillow under your knee, which you know I think feeds into the rationale, right? And their whole protocol in there. But let's start with this. Len, did you I mean, are you surprised that 57% of people have AMI?

SPEAKER_04 8:15

Um no, I mean it depends on how you define it. Like AMI, as we're seeing in the definitions, it's so it's a little broad, meaning, like, yeah, they're gonna have muscle inhibition. Basically, because of the surgery, it's just to what extent and is it reversible? Will it stay chronic and prolonged? Um I don't know. I thought it would be bigger. I don't know. Most people can't most people can't do a quad set uh actively or get that heel pop and all

Hamstring Fatigue Surprising Quad Boost

SPEAKER_04 8:42

that that uh Brendan just talked about. But um it was interesting the hamstring fatiguing stuff that's kind of emerging. Um, you know, in my head, and what we've kind of always gone after is getting that hyperextension through some passive, you know, um stretching, um, hamstring stretching, stuff like that. Um it was interesting that you know, hamstring fatiguing stuff, which I've dabbled with a little, and maybe I need to add it more in to kind of get the hamstrings to uh and even just like vibration. It's not even just doing a hamstring fatigue protocol with like exercise. I think it's just like vibration to kind of get the hamstrings slightly inhibited to get the quads uh activated and allow the the knee to get into that full extension. So it's little things like that that made me think a little bit more than what I currently do, which is, you know, stem, PFR, uh biofeedback, uh heel prop with weight on the knee and maybe gearing more towards um uh I think a hamstring fatiguing, as they call it, uh, may be kind of a new key for me in how I treat my acute ACL. So I thought it was an interesting paper. Uh classification system, you know, fine. I think it'll evolve over time. Um but I think most people are gonna have this. I think it's beneficial for most people to kind of go after, you know, some of the concepts that they talked about. And I thought it's a good, it made me think a little, which was good.

SPEAKER_00 10:02

Yeah, I thought the classification was you know pretty broad and subjective, like some of the nitpicking between like the various types is really really hard to kind of differentiate. But I I think it hits the main things. But uh yeah, totally agree on that. The hamstring concept, you know, we talk about like soft tissue vibration, you know, like hamstring type stuff, uh, contract, relax, like Brennan said, like just a PNF. I just thought was was was really cool. But like to me, like if did did you see the video like in the video in there in the article, um, they literally showed just fatigue out the hamstring, which by the way, is it probably gonna take a little bit of time to fatigue out the hamstring, but fatigue out the hamstring, and then all of a sudden, like the quad worked better. It was crazy to see, considering they did nothing for the quad, right? So and and and there's so many reasons why you can have this like building into this. So it's like, you know, we'll we'll add more to it. But just by working on hamstrings, the quad worked there, and you could see it in the contraction. They went from a rectus dominant contraction to like uh, you know, VMO VL. You know, you could see it, you could see the patella actually tracking. So I thought that was really interesting. But uh, what else? What do you guys got? Uh Kev, you want to jump in? Did you have something?

SPEAKER_01 11:10

Yeah, I was just gonna say that um when Brendan talked about the risk factors, uh, it was cool to see how many of those are modifiable from a PT education and treatment perspective. So, you know, if it's a short duration from the injury to the evaluation, we know that over time, if we're reducing swelling and pain, which were other risk factors, that it will likely get better if we kind of educate them on, you know, here are some things to avoid or a certain pain number to avoid, or during our exercises, you know, monitor for swelling and we'll make sure that we're doing the appropriate things to not prolong the swelling and maybe make this grade one go on to a grade two or grade three. Um, and then also just, you know, crutch education. And I know we all do this, like education about sitting with your heel propped up with nothing behind your knee. And even though it feels better

Red Flags PT Can Change

SPEAKER_01 11:59

to lay with something behind your knee, uh, we know that's gonna lead to issues with regaining extension and prolonging this issue. So I think that's that's awesome. I mean, there's a lot that we can intervene on. And then as the study showed, if someone is developing AMI uh or has this present from the time of surgery, it seems like a lot of them can be resolved uh through those different techniques. So I think it's uh like Lenny said, it's good to think about and have on your radar and you know, kind of keep doing some of the stuff we're doing and make sure that this doesn't, you know, prolong or worsen a little bit uh throughout rehab.

SPEAKER_00 12:35

Yeah, I love it. And you know, the crutches one. Let's talk crutches, though, because you said that's modifiable. But Len, I mean, we're starting to see some younger clinicians on social media starting to advocate like extended crush crutch use after ACL, which is crazy uh to think. But like I think this is an article showing that that would be bad. Like, what's your thoughts just on the crutches? Because I think we all we all know about ditching the pillow. I just think it's just great that we can say that there's a study, not a reference not to put a pillow under your knee. But what do you got on the prolonged crutch use? Because I I never would have thought we'd be having this conversation based on social media, but what do you think?

SPEAKER_04 13:11

Yeah, I'm torn. Um I think sometimes when I see people using crutches, and it's it comes down to my coaching and and and helping their gait, they tend to not put full weight on it, they kind of bend their knee, they kind of create almost like a uh flexion contracture

Crutches And Gait Tradeoffs

SPEAKER_04 13:25

by walking kind of on a toe instead of kind of getting that heel contact. Um, and it's kind of a it's just like we think we're doing well with putting crutches under the person to unweight it a little, but then it modifies their gait and it creates this kind of cycle that I'm trying to um work through. Um I tend to be, you know, get let's get rid of the crutches, let's keep you in a brace, let's unlock the brace, but the brace is there just to kind of help you. But I've seen people's gaits improve better, faster when they're in that brace, but no crutches versus the vice versa. That's what we're kind of seeing a little bit more right now. And I can't get people out of the brace kind of quick quicker, you know. I'm not having people exercise in a brace and PT. Um, you know, at four weeks, that brace is almost non-existent, and they are using it if they're in like a crowded area. Otherwise, they're not really using it um around the house or anything else, really. So um, I don't know. I I've kind of I'm torn with this prolonged use of crutches that I'm seeing right now and trying to work through it and see. Uh I'll have feedback sooner as I get more patients that are that are kind of going through this right now. But I think it almost is help, it's not helping us as much as we theoretically, you know, think it will.

SPEAKER_00 14:36

Not helping and potentially with some evidence like that. Slowing things down. Yeah. Right. Sure. Why why wouldn't you? You're you know, you're using the crutch as a crutch. A crutch. Crazy. Uh anyway, Dan, what do you got?

SPEAKER_02 14:48

I always wonder sometimes, this is kind of like a chicken or the egg kind of thing, right? So if someone has more pain, they're more likely to use a pillow, right? If they have more pain, they're more likely to use a crutch. If there's a worse injury, maybe it's more swelling, and subsequently have more AMI. Was it really the pillow or the crutches that cause the AMI? Maybe. You know what I mean? So I always wonder about that too. Um, but maybe it does give us a little bit of more, you know, firepower to get people moving and just let them know, like, hey, it's probably better to ditch this when you can. But I think the other thing is like probably don't want to throw the baby out with the bath water. Um, if the crutch is going to allow someone to walk a little bit better, reduce some stress in the knee, maybe they start having less swelling, less pain because they're offloading it better and their mechanics are still good. I would say maybe that it is something that's useful, but you probably have to read the patient that's in front of you. Um the one thing I will say too about this study is that it's kind of nice um to know that like, okay, well, if you're really painful and you come in, you're having a hard time, we probably need to focus more on that quad. So I think that was a little bit of a clinical takeaway for me that if I have a patient that kind of presents its way, it's like, okay, well, we probably need to be more focused on getting your quad stronger and um making sure that you're kind of prepared for your surgery. Because I think, Brennan, with these these are pre-op patients, right?

SPEAKER_03 15:57

Yep, that's right.

SPEAKER_02 15:58

Okay. And the other thought I had is to Lenny's point, it's like you know, only 50% of people have AMI prior to surgery. I guess that makes sense. That's always surprised to me after people have an ACLTR complete that they sometimes can look pretty good, present pretty good, right? But after the surgery, pretty much 100% of people I would assume have AMI, right? Just because the nature of the surgery and the damage it causes. So maybe it just speaks to um I don't know how to word this without making it sound poorly, but the damage that is caused by doing surgery, right? Which obviously it ends up being beneficial, but um just speaks to the what happens in surgery uh in relation to what happens when you actually tear it the first time.

SPEAKER_04 16:36

Can we touch upon the previous history of ACLs that showed a significant decrease? I think there's something to that, and I don't know what we're talking about here. Is it that their system is already downregulated from the previous ACL? Or is it like the mental component of I've gone through it, I know what's coming up, and I'm okay with it, I know what to expect in pain and all that? Like what do we not that you can control your body that way, but is there some kind of somatosensory kind of you know issue that we're seeing in patients that already have experienced it and like ah, here we go again, but I'm fine with it, let's go, versus the I've never had an ACLT, everything gets shut down, you know, it's it's it's traumatic, it's bad, it's I don't I don't know. I I I I don't know what to think of all that, and I I want people to kind of help me with that.

SPEAKER_00 17:22

I don't I don't have an answer. I mean I know, but

Prior ACL History Lowers Risk

SPEAKER_00 17:26

what do you think, Brandon?

SPEAKER_03 17:27

Yeah, so from my understanding from the paper, uh they made the um kind of assumptions that it it showed either uh a CNS adaptation from the first injury, so your brain pretty much found a way to work around the AMI because it had experienced it in the past, and then you have these neural adaptations. They they kind of hedged a little bit and said there could also just be local joint changes, like there's less nerve input um or there's damage proprioceptors too. Um so that changes the sensory input. Um, but I also wonder too, like when you know, I've treated people in the past with AMI and you you get them on the NMES, you get them with the strap, and you're like really working on that more cortical inhibition, and you're working on getting them to put more effort into contracting their quad, you know, they can pick it up within a session, right? Yeah. Um and then maybe have to work on it some more. But I wonder too how much of that is the learned behavior um for the first time as you go around. Um, but that's at least what the paper said.

SPEAKER_04 18:22

Because they also said it was ipsilateral or contralateral. So it doesn't matter if it was the same knee or the other knee, they did better overall, you know, so it's not like the there was damage if there was the ipsilateral knee, but the contralateral knee. I don't know, it's just it was it was interesting the fine the finding.

SPEAKER_03 18:40

They had said uh in the paper if it was iptilateral, there's a a higher, or excuse me, there's a lower risk compared to the contralateral, but both of them were factors that were associated with less risk of AMI.

SPEAKER_00 18:52

Yeah, yeah. Um makes sense. Yeah. What else? Anybody got anything else on that one? I like that article. It was pretty good, right? Brendan, good review, appreciate that one there. I think you know, this this is you know good evidence to support some of the things we're saying. I think we kind of know all these, you know, things to an extent, but I think, you know, you know, the hamstring protocol, I think was a little bit more um, you know, highlighted for me. Um, you know, to Lenny's point, like, you know, we do hamstring soft tissue, you know, we started doing more vibration. Um, but yeah, sure, you know, it looks like that hamstring inhibition is probably more related to you know some of these factors, and maybe we give it credit sometimes. So, you know, it's definitely part of like a comprehensive package that we can do to work on these. And then for those stubborn ones, right, then we know we got to dig a little bit deeper, right? And maybe those are the people we start throwing some other things at. So um, you know, it's kind of a way for us to tell, like, if you can clean this up, like to Brendan's point, just by like some some quick motor control education during one session or fatiguing out the hamstring and it cleans up a little bit, you know, you got you know a little bit easier road to go down. But if you're struggling, maybe we need to double down on some of the stuff we do early. So um great stuff. Thanks, Brendan. Really appreciate it. If you're liking these articles, please let us know. You know, comment on social media, these types of things. We see them. Um love to hear more and you know the feedback on these articles. But we're having fun, so hopefully we'll we'll keep doing them. And please rate, review, subscribe, Apple Podcasts, Spotify, whatever you listen to, and we'll see you on the next episode.