Something ACL patients, really any knee surgery patient, struggles with the most is regaining full knee extension. Out of surgery, many lay their legs straight, and one knee looks like this, if not worse.
Next thing you know they’re walking like this,
We’re talking not only the ability to straighten your leg, but the ability to hyperextend your knee. If straight is zero degrees, then hyperextension would be another 7 degrees, give or take. Rather than your ankle and knee being lined up, your knee can go a little behind your ankle.
(You do not want to work on your knee range of motion while standing though!)
I’ve had the amazing fortune of spraining my knee, having reconstructive ACL surgery, and having a partial meniscectomy. I have, for the most part, seen the gamut of knee injuries, personally and professionally.
Excluding extenuating circumstances, like complication from a knee replacement, by far the hardest time to regain knee extension range of motion is after ACL surgery. It was something I needed to work on every hour of every day (not hyperbole), for the first 6 weeks after surgery. It took until about the three month mark where I didn’t need to worry about it multiple times a day. By worry about it, I mean if it wasn’t done at these time intervals, I’d lose the range of motion, and it could take many minutes of stretching to regain it.
Many experience the same thing. Although, some regain full range of motion like it’s nothing. Beyond the readily apparent, like pain, inflammation, why is this so hard? Why do some have no problem at all? Is there anything unique to ACL surgery making it tougher than other injuries?
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What does the anterior cruciate ligament do again?
The ACL goes from the back of the femur to the front of the tibia.
The ACL subsequently prevents the tibia from going in front of the femur. It pulls the tibia back to the femur.
To test if an ACL is torn, you’ll see an orthopedist gauge how far they can pull the tibia forward relative to the femur.
If it’s really lax, there’s probably a tear. (Why you don’t want a non-orthopedist testing your ACL.)
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What happens to the ACL during knee flexion and extension?
I am simplifying this some. If you want more details, such as breaking the ACL into anteromedial and posterolateral bundles, check the Wheeles discussion. That level of specificity isn’t needed here.
As the knee bends, the ACL is tautened as the tibia moves forward relative to the femur / the femur moves backward relative to the tibia.
This is one reason there are often, though not always, flexion range of motion restrictions immediately after ACL reconstruction. You go bending the knee too much, you might stretch out the graft.
When coming into knee extension, particularly some hyperextension, we can again see the femur moving back relative to the tibia. Really watch the last bit of this animation:
GIFs made from this video.
The more obvious: When you get a new ACL, the graft is tautened when put in your body. Your range of motion can be based on how tight the graft is. A really tight graft and it may be harder to work on flexion and or extension range of motion
The less obvious: I recently went in into an operating room and watched an ACL reconstruction. There are a couple moments where you knew the surgeon was tightening the graft. He would let out a huge grunt, like he was lifting heavy weights. As he jokingly said, “When you grunt, that’s how you know it’s tight!” The idea is this thing is really, really put in there.
-> In dogs, a veterinarian surgeon has told me they’ve given up on reconstructing the ACL. Due to the dog’s anatomy, their physical strength, and how hard it is to manage a dog post-op, they too often rip or stretch the graft. This another reason in humans we don’t (or at least shouldn’t!) go running like crazy a month post-op, or only do things based on pain. We need to give the graft (typically a tendon) time to set in the bones, as well as time to transform (into a ligament).
Not only that, but during the final phase of surgically inserting and tightening the graft, the tibia is pushed backwards relative to the femur.
- Pull the tibia forward relative to the femur => ACL tautened
- Push the tibia back relative to the femur => ACL slackened
Meaning the graft is tautened in a position the ACL is usually slackened. Tighten graft -> Push tibia back relative to femur to slacken graft -> Then tighten graft again. The new ACL is put in tighter than a normal ACL would be.
This was being done by two grown men at the same time. One guy was working with the femur and tibia, the other guy was working with the tibia some, but also finishing up on the graft.
-> I got more of an understanding why orthopedic surgeons plan to retire by 63 years old. It’s a physical job.
Two men putting the leg into position, specialized materials apparently stronger than anything in the body, with one guy using damn near all the strength he has. That’s how this thing was put into place. This is thing is put in tightly.
Beyond wanting the graft secure, the idea here is despite all this, over time, the graft will likely still loosen up some. By placing the graft in a position where the ACL is actually a bit shortened, as it loosens up some, it will then be in a normal resting position. It’s a fail-safe; attention to detail at the highest level.
But going back to our knee extension range of motion, what do we know happens as we approach some hyperextension?
The ACL stretches a little bit. Our knee has just been manipulated with two men using super strong materials to hold their manipulation, which prevent this anterior tibial translation. No wonder it’s hard to get knee extension range of motion back!
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Fear not?
We often worry about bending the knee too much too soon, but we don’t worry about straightening it too much, too soon.
By regaining knee hyperextension range of motion, we’re talking only 7 degrees or so, relative to neutral. The graft is placed in a position where it’s expected it can loosen up to this point. Furthermore, the force on the ACL is quite small in hyperextension. Maybe 10% of what the ACL can handle. (Initially, something like a quadrupled hamstring graft is stronger than a standard ACL. So they often have an even better ratio in this regard.)
In knee flexion, we’re talking up to 120 degrees, relative to neutral, and the ACL is the primary restraint to anterior translation of the tibia from 30 to 90 degrees. Accounting for 80% of the work. Furthermore, anterior tibial translation -stretching the ACL- is greatest between 20 and 45 degrees of knee flexion.
There is a significant discrepancy in ACL stress, and range of motion, between going to full extension and full flexion. This is one reason some will end up locked in a brace for 10-14 days, before being allowed to bend the knee. The decision is to eliminate all bending to minimize ACL stress. But that bit of stress in full extension? Not worth worrying about, and regaining full extension is much more important than full flexion. The cost / benefit of stretching the graft versus regaining full extension is clearly in favor of full extension, while the cost / benefit of stretching the graft versus regaining full flexion is in favor of being careful with knee flexion. Particularly active flexion, where passive isn’t as much of a concern.
-> For 8-12 weeks is a good ballpark. Patellar graft is believed to be set by ~8 weeks; hamstring graft by ~12 weeks.
–> Takes ~18 months for them to transform to a ligament though!
-> If you’ve had a meniscal repair, common with ACL pathology, you’ll want to be even more careful with knee flexion, as flexion mobilizes the meniscus.
That said, this doesn’t happen to everyone. Even the surgeon I watched, when I asked him about locking people straight, he said it was mainly to let the leg calm down more than anything else. It seems some feel good enough about the graft, or the materials they’re using, they don’t worry about range of motion after surgery. (Passive range of motion. Everyone worries about active, and how intense the active is.) Although, you’re unlikely to see anyone allowed to bend past 90 degrees for at least a couple weeks. The swelling probably won’t let you anyways.
I’m not sure if every surgical team does things this way, where they place the graft in a position of being extra taut. I unfortunately didn’t think to ask this question at the time, although I’m not sure they would have known. My impression is this isn’t always done, and this is why some people may not have as hard of a time regaining range of motion immediately post-op. However, their graft may not be as well set as someone else. It’s quite possible having trouble regaining knee hyperextension after ACL surgery is a sign the surgical team did a good job, and that if you regain things too easily, things may not have been as well set as they could have been.
With the body, it remains whenever you gain something, you lose something.
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For a plan dedicated to making the initial ACL recovery as smooth as possible, go here.
For a plan focusing solely on being able to straighten your knee again, go here.
joe
February 27, 2017
can muscles tightening or shortening cause knee extension loss and knee pain?
i am getting deep tissue massage to try stretch out my knee after losing range o motion after acl surgery 8 years ago..
my last surgery was actually to remove the acl graft, not sure why they removed it
can i live a normal life without an acl?
also, do you thin massage will help regain knee extension?
thanks for your time, looking at buying your book. If you can answer any of my questions it would mean alot to me
thanks!
reddyb
February 28, 2017
Stiff hamstrings can cause extension issues. But after surgery it’s much more the joint gets stiff than anything else. When stretching the knee into extension the hamstrings are not fully stretched ( https://b-reddy.org/2013/07/29/better-exercises-to-stretch-the-hamstrings/ ), yet the knee won’t fully extend => joint is what’s causing the lack of ROM.
As well, while feel is not always indicative of what’s going on (e.g. https://b-reddy.org/2011/07/21/just-because-it-feels-tight-doesnt-mean-it-is/ ), pretty much anybody working on their extension will also tell you they feel the stretch in their knee, not their hamstrings.
Massage is more likely to be helpful with knee flexion than extension e.g. if the therapist helps move the fluid around, giving the knee some more potential to move, flexion can more easily improve (right after doing the massage. that fluid will come back not long after.). This can moderately help extension too, but fluid is not a hindrance to extension ROM like it is flexion. By no means necessary though. And any benefit is likely to be marginal. For those who like massage, want some help relaxing, enjoy someone rubbing on their body, then it can simply feel nice. But it’s very unlikely to be a noteworthy difference maker.
Life without an ACL:
https://b-reddy.org/2011/12/05/reconstructive-acl-surgery-is-it-worth-it/
https://b-reddy.org/2011/11/29/reconstructive-acl-surgery-is-it-beneficial/
Joe
February 28, 2017
Thank you for such an in depth response. You make alot of sense.
Is it possible to regain my knee motion after 8 years…is it supposed to hurt ( a ton but of sharp pains) while stretching?
Last question…who do i need to see if the massage therapist wont do the trick? Will any physiotherapist know how to regain extension or do i need to see a specialist of some kind?
Thanks so much for your time!
reddyb
March 3, 2017
Guide to regaining extension here (talks about pain, timeline, and more)- https://b-reddy.org/2015/09/03/help-i-cant-straighten-my-knee/
If doing something like that, dedicatedly, for three or more months doesn’t do anything, then you’d want to see an orthopedist.
Vinu Gautam
May 3, 2017
Sir after three months of acl i can move my leg by 150 degree.is it good or need some improvement?
reddyb
May 5, 2017
Not sure what you mean by 150 degrees.
Normal knee range of motion is about -5 degrees (hyperextension) to 125 degrees (knee flexion).
Alok sharma
April 12, 2018
Hello sir I had my ACL surgery done on 31st march 2018 & got discharged on 3rd April 2018…post discharge I was wearing knee braces for 2 days but on 3rd day undeveloped swelling above my knee so I stopped using knee brace & started using Compression stockings on advice of my doctor ….also while doing my physio I m unable to touch my Calf muscles on ground ….its a little above the ground ….wat to do??
b-reddy
April 13, 2018
Hey Alok,
I would check this out: https://b-reddy.org/the-most-important-phase-of-acl-rehab-copy/
Louise
June 8, 2018
Hi Brian
What absolutely fantastic articles. Thank you so much for taking the time to document all this information and advice for our benefit. It would’ve taken you hours to do!
As most others here, I had ACL reconstruction surgery and meniscus ‘shaving’ (I was told about the latter by the orthopedic surgeon after my surgery) a week ago. I’ve got to be honest, I am absolutely paranoid about not being able to straighten my leg again. I did the injury (to my GOOD knee) playing tennis = sprinting over and then stopping suddenly in an attempt to prevent my opponent’s ball from interrupting the game next to us. In hindsight, I should’ve and wish I had’ve just let the ball go 🙁
Anyway, I purchased your manual this afternoon (I’m in Western Australia), and I’m just wondering how and when I will receive it please?
Cheers and wishing you all good health and a speedy recovery.
Louise 🙂
b-reddy
June 12, 2018
Thanks Louise! Hours indeed :).
You should have received an email with a password for the manual. It may have gone to spam? Or sometimes a person accidentally mistypes their email. Let me know if you’re still having issues. Feel free to email me: b-reddy@hotmail.com
Fredrik
December 12, 2020
Hello Brian,
Thank for outstanding information and insights and nuances. I’m a 38y old, 9 days post ACLR with a STG but without any other issues in the knee. I had full ROM before surgery and were mostly normal after been trying to rehab my self out of surgery for 6months but wasn’t able to go back to pivoting or competitive hockey without swelling/pain. After surgery I knew I had to focus on regaining full extension. So when getting there passive in 7 days by trying to keep the leg as much as possible in a passive stretch with a pillow under the calf/heel instead of under the knee I’m now instead worried I somehow stretched my graft or that is wasn’t properly set as you mention in the end of the article. Sure it wasn’t comfortable keeping the leg passively stretched but it subsided after a week and now I’m principally pain free, still a bit stiff but feeling it was to easy. I’m near 90 degrees flexion but isn’t pushing it at all to not risk stretch the graft any further if that’s the case. There is so much contradictory information out there it feels impossible to get it right. Is it possible/unusual to have a more or less straight knee after a week already and not having much pain or do you think it likely contributes to additional laxity in the future? Is your timeframe for knee extension in relation to active TKE?
Thanks again for your fantastic articles!
/Fredrik
b-reddy
December 15, 2020
You ideally will be having a follow up with the surgeon again soon, and some more appointments after that, where they should be checking the graft, which will hopefully give you some peace of mind.
Some people have little to no issues with ROM, even after surgery, whereas others stiffen up like crazy. This can be at least partially due to some people are bigger swellers than others, and those who swell more are more likely to have ROM issues. Regardless, there’s no hard rule as to how difficult it will be to regain ROM. It definitely varies. The only almost hard rule is that if ROM is not worked on, the knee is going to stiffen up. Even then I’ve seen some lazy people have great ROM after knee surgery.
“Difficult” also requires context. For example, with my own knee, getting full extension wasn’t all that difficult, it was keeping it. I could do a stretch for a few minutes, get full extension, then an hour later have lost it and need to do it again. I had to do it practically every hour for a couple months before it finally started to “stick.”
I’m not sure what timeline you’re referring to, but extension ROM here is meant only in the passive context.
Getting to full extension 7 days out may be a bit fast compared to a normal person, but that’s only because the average person gets their extension back too slowly. Ideally, full extension is had the day of surgery. (Flexion is very different.) Many would say getting full passive extension ROM 7 days out from surgery is actually a bit slow.
Pain also varies tremendously. Interestingly though, the more prepared a person is going into surgery, typically the less pain they’ll have coming out. (I personally had virtually no pain after surgery.)
Hope that helps.