An important concept to master ACL rehabilitation is to understand the normal healing process of an ACL graft.
Different grafts heal at different rates depending on the tissue and fixation method.
Here’s what we know about the healing rates of ACL autografts.
To view more episodes, subscribe, and ask your questions, go to mikereinold.com/askmikereinold.
#AskMikeReinold Episode 279: Strength of ACL Grafts Over Time
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Show Notes
- What is the Best Graft Choice for ACL Reconstruction?
- 6 Keys to the Early Phases of ACL Rehabilitation
Transcript
Student:
All Right. You got Jeff from Washington DC. He asks, “When it comes to ACL grafts, can you speak to the strength of patella tendon grafts versus other autografts over time, including any weakening caused by remodeling of the tissue?” And as a bonus question, how the strength of the graft sites for patella tendon, hamstring tendon, and quad tendon are impacted.
Mike Reinold:
You know, Jeff, you snuck two questions in there and that it’s a faux pas. Right? That’s a podcast faux pas. But no. Awesome. Good questions together. I think that’s pretty good. This is one of those ones that if we go through the decades of research, I think we do have some of these answers, but I like it. Len, let’s see how much you can tackle and see if we even need to add anything to this. But ACL grafts over time, the strength of the grafts of an autograft over time, how strong are they when we first put them in? What happens over the course of the ACL? Give us the rundown.
Lenny Macrina:
Yeah. Here comes the rant. No, this should be nice. This will be peaceful. Does matter? I feel like.
Mike Reinold:
Oh, that’s not peaceful or nice.
Lenny Macrina:
I know.
Mike Reinold:
You just threw it back at him.
Lenny Macrina:
To me, it matters, but we don’t treat it like it matters because if you look at the research, the graft is strongest when you put it in. So it’s stronger than your native ACL, whether it’s a patella tendon, a hamstring tendon, or a quad tendon. And so when you put it into the knee, it’s stronger than anything you were born with. And so over time, it is thought to weaken. It’s ligamentizing. It’s a fancy word for just becoming a ligament and realigning its properties to be more ligament-like versus a tendon. But I think it still stays stronger than your native ACL. The problem is when it’s going through this process of ligamentizing, it’s weakening, so to speak. There’s some theories of the first six to eight weeks, you can stretch out the graft.
Lenny Macrina:
That’s why a lot of docs don’t want heavy knee extensions and heavy anterior tibial translation early on. But in general, they’re all very, very strong and stronger than anything we know. I actually just put stuff out. I don’t want to date this episode, but recently on social media, I put up some stuff that there was a study on sheep ACL, which I know it’s sheep. But it showed that they over a year, two years, which is what we think it takes for this ligamentation process to occur, that the graft is not as strong. The graft will weaken more to the point than your native ACL. So now it’s cause for concern, is are we pushing it too much by, I don’t know, doing plyometrics at 10 weeks or running at 12 weeks roughly. So all that stuff is always in my head of, are we doing a disservice? Never mind female-male, the same review paper shows that female ACLs, their native ACLS have more… they’re not as stiff as a male ACL. So maybe that’s a connection why females tear their ACLs more than males.
Lenny Macrina:
All this stuff is roughly in my head when I’m rehabbing people and I’m trying to monitor their amount of translation, but still, I don’t have a KT. And we just use these as rough guidelines. Because I don’t think we a hundred percent know. A lot of it is on animal studies, not necessarily humans.
Mike Reinold:
Yeah. I was going to say that about the sheep, Len. I don’t think the sheep went through the same protocol that us humans go through. Right?
Lenny Macrina:
Yeah.
Mike Reinold:
I think they went back to being sheep day one. And that was probably part of the process. So who knows? Maybe their grafts never got a chance to heal well, because they were sheep day one. I don’t think they were non-weight bearing with a nice brace. I don’t think they were working on their quad control.
Lenny Macrina:
Right.
Mike Reinold:
Do they have quads? I don’t even know. Do they have four quads, so quad quads? I don’t even know. I’m not a sheep guy. But that’s a tough study with those sorts of things.
Lenny Macrina:
Correct.
Mike Reinold:
I think we got to be a little careful of stuff like that.
Lenny Macrina:
Cautious. Right.
Mike Reinold:
Okay. We got a little off topic but-
Lenny Macrina:
Shocker.
Mike Reinold:
So that is the graft strength?
Lenny Macrina:
Yes.
Mike Reinold:
What about fixation though? So you come in, all of a sudden those two bones aren’t touching or worse, the soft tissue graft that’s just tied in there, that fixation strength isn’t strong. The graft is strong on day one, but the fixation strength is a weak point. Am I off on that?
Lenny Macrina:
No. And you’re making my argument why I recommend patella tendon grafts. I don’t know if I have old-school thinking or I have misinformation, but I just feel like patella tendon graft because the bony bone interface in the tibia and the femur is it just heals in six weeks. And that’s a nice way for blood to get into the patella tendon to help with the ligamentization process and just graft incorporation and graft healing and things of that nature. And maybe that’s why we see a hamstring graft stretch out just a little. If you look at some studies, there is more laxity in a hamstring graft. And failure rates are higher in hamstring grafts. I agree that I would recommend a bone patella tendon-bone graft for most of my clients, unless they’re older in a hamstring or they’ve already used a patella tendon graft, then I’d probably recommend a quad tendon.
Lenny Macrina:
But yeah, I agree. The graft is stronger than your native ACL. The graft fixations, I think an important concept to remember just because of how it’s going to incorporate in the knee and how quickly it’ll incorporate. And I think it’ll allow you to maybe go a little bit faster with your rehab because we go the same speed with hamstring and patella tendon, but the hamstring graft doesn’t incorporate for weeks, if not months after the patella tendon. I think it’s even longer than we think. I think we’re looking at a two-year process of incorporation, not just six weeks or 12 weeks. I think it takes longer than that. That’s what some of the research has shown. And we talk about this in our new seminar courses. There are some slides that talk about that it takes longer than six weeks or 12 weeks. This is a year or two process at least.
Mike Reinold:
Yeah. All right. Let’s get to Jeff’s question and actually try to nail down the timing. Day one, the graft is stronger than your ACL-
Lenny Macrina:
Strong as a bull.
Mike Reinold:
… but the fixation is not.
Lenny Macrina:
Yeah, correct. Right.
Mike Reinold:
I think it’s a little misleading to say on day one, it’s strong. Because I don’t think that the ligament plus the fixation together as a team is strong.
Lenny Macrina:
Right. I think if you took the graft and you tried to break it-
Mike Reinold:
Right.
Lenny Macrina:
That’s what I’m talking about is strong, but yes, you’re only limited by the whole section of the graft, which is the bone and everything else. Yeah.
Mike Reinold:
Yeah. So clinically that’s why we’re cautious at the beginning is because the fixation strength isn’t there and that is perhaps why a lack of a bony interface, like with the patella tendon and even a quad tendon on one side, maybe that’s why those don’t do as well is because they have such a long period of time where fixation is not there. You have to be careful with that. So that’s day one. The graft itself gets weaker, but then the fixation gets stronger over that first initial period. Right?
Lenny Macrina:
Correct.
Mike Reinold:
So bony tunnels, when do you think they heal up, Len? Six weeks? Eight weeks?
Lenny Macrina:
I would say six to eight weeks, depending on the health of the person. If they have comorbidities, diabetes, something like that, then it might be limited. But I think in general, bone heals in six to eight weeks. I think that’s what we go with is that timeframe. And that’s where I tend to do a little bit more faster relatively maybe with a patella tendon graft than a hamstring graft. I think maybe that thinking is from the fixation. I think Kevin talks about that a lot too. It’s always been in my head and it’s always something I see in the research. It’s just the fixation strength. That’s what you’re limited by, not necessarily the pull. Hamstring tendon is stronger. It’s like 4,000 Newtons compared to a native ACL, which is like 2,200, whatever it is, 2,500 Newtons. A hamstring is much stronger than a tendon or maybe even a quad tendon, though the quad tendon is much more robust, but it’s just the fixation.
Mike Reinold:
Yeah. So why do they get loose and why do they fail more is because of the fixation.
Lenny Macrina:
Right.
Mike Reinold:
As a whole, that’s why we say, again, be careful when we say, “Well the hamstring is stronger.” The graft is, but the fixation isn’t right.
Lenny Macrina:
Right.
Mike Reinold:
Right. And you put that together, that’s a big deal.
Lenny Macrina:
And nevermind, you’re taking a hamstring from somebody that’s not their dynamic stability, which is helping to maintain posterior translation, prevent anterior translation. And you’re taking dynamic stability from an organism, a human that’s trying to get stronger and now they are going to be weaker because you took one of their tendons out, which now the muscle has nothing to attach to the bone. Some would argue that the tendon does grow back, but it’s not as supple as your native tendon that was just removed if you had a hamstring graft.
Mike Reinold:
All right. So it’s six to eight weeks out. A bony fixation is healing, but the graft now is weaker. Right?
Lenny Macrina:
Yes, weaker. Yeah.
Mike Reinold:
Then when we first put it in, because it’s going through that ligamentization process where it’s actually right to change. So now the tissue is engulfed, sometimes it’s even swollen. Sometimes you have some of a healing response to it. So that’s actually at a weaker point. That’s why we go a little weaker. But Lenny, are you saying that’s still stronger than the native graft?
Lenny Macrina:
Newton-wise, yes, from what I understand. Yes.
Mike Reinold:
That’s cool.
Lenny Macrina:
It is.
Mike Reinold:
That’s that good to know.
Lenny Macrina:
Right.
Mike Reinold:
All right, let’s go to the soft tissue grass with the hamstrings then. When do you think that starts to incorporate within the tunnels with the fixation strength of the procedure?
Lenny Macrina:
Right. I don’t know a hundred percent sure. What we know is, I would say I roughly use 12 weeks. Tendon tends to heal the bone roughly in three months, roughly. Again, it depends on the person, but with a rotator cuff repair, tendon healing to bone when we’re trying to repair a cuff or a patella tendon or any other tendon in the body, it seems like it takes about 12 weeks to really feel comfortable, to be more aggressive with the person. But again, I think some of the studies that are in our new seminar course, and that are out there from 2011, [inaudible 00:11:39] 2011, another study in 2013, is showing all these animal studies and other studies show, it takes a year or two for incorporation to be a hundred percent complete, two years for these grafts to really begin to look normal.
Mike Reinold:
And I think it shows that too with Tommy Johns too, and the elbow and stuff.
Lenny Macrina:
Right. Yep.
Mike Reinold:
It’s interesting. I don’t know. Jeff, keep that in mind when we talk about the strength in here, it’s not just the strength of the graft, it’s the strength of the fixation. It evolves over time, but we have to talk about probably what’s clinically relevant. The strength at three months versus six months may not be that much different, but maybe some of these concepts will help you with your early phase rehabilitation.
Lenny Macrina:
Which is a reason why if you see a lot of our protocols, the first six weeks is a healing phase, six to 12 weeks is kind of bring them along slowly, stress the tissue. It’s not until about 12 weeks that you start to see in our SLAP repairs, which we don’t do a lot anymore. But Tommy John’s, ACLS that you start to see that next level of strengthening in the next level of really applying stressors to the area. That is the reason why is because we think some of that tissue takes at least 12 weeks to heal. It’s not just like we’re pulling stuff out of the air. There’s a method to the madness.
Mike Reinold:
And the fixation starts to take.
Lenny Macrina:
Correct. Right. Exactly.
Mike Reinold:
I think that’s the important part which is that.
Lenny Macrina:
Yeah, right.
Mike Reinold:
Awesome. All right. Jeff, I hope that helped. If you have a question like that, head to mikereinold.com, click on that podcast link and you can ask away, just fill out that form. Anything you guys want to talk about, we’re here to answer your questions. Please, head to Apple Podcasts, Spotify, rate, review subscribe. We’ll see on the next episode. Thanks so much.
