About the author:

Howard J. Luks, MD

Howard J. Luks, MD

A Board Certified Orthopedic Surgeon in Hawthorne, NY. Dr. Howard Luks specializes in the treatment of the shoulder, knee, elbow, and ankle. He has a very "social" patient centric approach and believes that the more you understand about your issue, the more informed your decisions will be. Ultimately your treatments and his recommendations will be based on proper communications, proper understanding, and shared decision-making principles – all geared to improve your quality of life.

79 comments on “Why Can’t I Straighten My Knee?

  • 7mths post MPFL repair with TTO is it common to still have severe pain stiffness and inability to straighten fully.
    I wonder if i have sustained a further injury as you suggest here, although i havent had a specific accident/injury as such

    • No, actually not common. I would consider having a second opinion with a doc who treats patella-femoral issues regularly.
      Good luck

  • If it is a bucket handle tear that is preventing straightening of the knee, will that be picked up by an MRI?

      • I have been having really bad problems with my right knee when I bend my knee it locks after a while and it is so hard and really Herts when I bend it back it been getting worse it been happen for about a year and getting worse and clicks when I move my leg back and forward

      • Sorry to hear that Robert…. sounds like you need to see a good Orthopedic Doctor to check out your knee.

  • I haven’t been able to fully straighten my knee since October 2016. I had a scope for scar tissue February 1, 2017. Even after surgery my doctor still couldn’t straighten it more than 30 degrees when I was under anesthesia. I have p.t. daily and even now it wont get straighter than 30 degrees.. any suggestions?

    • I’m sorry Allison, this sounds complicated. I would only be able to offer you an opinion after I saw you in the office.

  • Can straighten my knee but is a little painful. Walking on it hurts more and I limp. Could this be something that will pass with time? Should I wrap the knee?

    • A compression sleeve might help, and a course of PT might help too… ultimately you should have a good exam and an Xray to see what’s going on.

    • Did you ever find out what the issue was and how did you recover? I’m having similar issues now.

  • Hi Howard.
    Hi Howard,

    I am 6 months post ACL reconstruction surgery after a pivot shift injury. I also sustained large lateral meniscus tears “There is a large tear of the posterior horn of the lateral meniscus. There is a displaced fragment extending from the posterior root attachment into the intercondylar notch., adjacent to the lateral femoral condyle. In addition, there is a large flap tear displaced superiorly into the superior gutter, adjacent to the body of the meniscus”.

    The surgeon used a patellar graft for the new ACL, but decided to leave the meniscus as is. Although since the surgery I cannot straighten my knee and almost locks when I am sitting for extended periods. The pain on the outside of my knee has made it hard to do my rehab.

    Would removing the meniscus be the next option? My surgeon mentioned before my surgery that he may have to do this down the track. I am a competitive sprinter, how would removing the meniscus affect my return to elite running?

    Thank you!!

    • HI Aaron…
      Removing a portion of the meniscus could have a significant impact on your ability to compete as an elite. The meniscus has an effect on stability, and weight or force distribution across your knee. The risk of developing arthritis is significantly elevated after a partial menisectomy. Some of these root tears are repairable… Some can be safely ignored at surgery. It’s a tough call. Perhaps you can find another opinion about the repairability of the tear?
      Good luck

  • Hello DR. Luks,
    First of all thank you for taking the time share with us you knowledge.
    I am 7 days out from meniscus surgery (simple scrape it out 25 minutes). when I try to straighten out bend my knee on the back (hamstring?) of the knee I get a tearing feeling and increased pain. Could I be tearing something our is this something that just needs to be worked out? Is it to early to be riding a stationary bike at the lowest setting?
    Thank you again.

    • Hey Ken,
      Sorry that I can’t comment on post operative exercises.
      It is not unusual to have unusual pain in various area after surgery.

  • MRI did not see meniscus tear but my knee will lock during some physical activity (martial arts) and i cannot straighten unless i bend leg side to side it often is instantly relived and fine. Ortho thinks its hamstring locking over tendons. MRI saw a tear in hamstring. can hamstring snapping cause the locking or just meniscus tear? not in constant pain just locks in bent position, but i can easily relieve…

    • There are many common reasons why I knee might lock — > such as a mensicus tear. But there are other less common causes, such as a case of snapping hamstring tendons, a loose body in the knee, as well as issues with your kneecap or patella.

  • I hurt my knee around 5 weeks ago when I was playing basketball I boxed out a larger guy and I felt my knee go weak and started limping so I subbed out.. after the game my knee started locking and it felt so weak.. even now I can walk perfectly I can lift heavy weights to a certain extent but some times my knee will lock if I walk awkward or land awkward..
    When I run or jump it will hurt also I think it’s a tendon issue because the pain is located on the high end of the knee near where the thigh meets the knee. Could you help me..

    • HI John…
      While I can not diagnose from afar, I can say that you should have this looked at. Not being able to straighten your knee for 5 weeks is something that a sports medicine Orthopedist should get a look at.

  • Hello
    Total acl rupture and bone bruising as well as bleed in joint etc
    7 weeks after injury cannot over extended leg still (ie. lying down with legs straight cannot raise calf off floor)cannot fully push knee back when standing
    High pain when trying to crouch…cannot do it…bad pain behind knee on on external side bone…and the liquid looks about ready to burst out of the joints when knee is bent

    Is this normal at this stage? The swelling is still there…cannot raise leg and pain is excruciating in certain positions…
    I’m in physio but we are strengthening quads etc…

    No one seems particularly worried about pain…swelling…

    Thanks for your opinion

    • If the meniscus was normal… then continue with physio. Some people stay stiff longer than others after an ACL tear.

  • Hi Doc,
    About 4weeks ago I was using a staircase and I had painful movement within my knee, i was able walk fine that day but when ever I squat or kneel, it’s difficult getting back up with my knee straight immediately. Then the next day while standing the same painful movement occurs, this time it doesn’t straighten. I went to the hospital and had an X-ray but the doctors say my knee is normal and I was given drugs. Presently the knee straightens but not fully but there is still pains and whenever I remain in sitting position for too long I find it difficult to immediately straighten my knee without pain.

  • Hi Howard,

    Its been 4 week now that I’ve been diagnosed with MCL partial tear (Grade 2). I’m also using knee brace to prevent its lateral movement. I’ve been on rest since the time of injury, and still I’m not able to keep my leg straight or put body weight on it.
    How long does it usually take to heal completely and get the leg straight?

    • MCl tears can take many weeks to calm down. Talk to your doctor to see if they think that a physiotherapist would help you achieve better motion.

  • Last week I started waking up with terrible pain in my left knee that has gotten progressively worse. When running, I have been taping my knee and that seemed to do the trick until today. When I was about 5km I suddenly was in more pain than I care to admit but had to still get back home, another 4 km. I immediately iced my knee and it seemed to help I could bear weight on it almost normally the pain was reduced and I could bend and straighten it with a tolerable pain level. I went out for less than an hour and it now feels worse than ever despite taking my break through pain killer. I did notice a fair amount of swelling on the inside of the knee and once again have it wrapped in ice. Should I be concerned about this?

  • Hi, couple weeks ago i was playing hockey, im a goalie. Anyways I went to move side to side with considerable force and my knee had this intense popping sensation .. I’m going on my third week now, they said my mcl is a grade two tear, but i can’t straighten my leg out back to normal. Refuses to go back like its permanently stuck. Its always bent, advice?

    • MCL tears can hurt a lot. Many MCL tears take time getting back to full extension. At some point in time some docs may proceed with an MRI to make sure they are not missing a bucket handle meniscus tear which could also cause loss of extension.

    • Hi Matt!
      Just wondering how you made out….
      I am 3 weeks post injury and cannot fully extend my leg beyond 30 degrees
      Going to PT 2 weekly but not much more is happening in terms of healing
      Any advice would be helpful :)


  • Hello, I should start by saying what caused this particular injury has happened to me before about 5 times. What happens is, it feels like the outer part of my left knee dislocates? I’m never doing anything particularly strenuous, just walking/standing up etc. Usually I just forcefully straighten my leg, I feel a pop, and it’s fine. Sore for a few days but nothing a brace and ice won’t take care of. I was looked at my an orthopedic doctor 3 years ago, who did an MRI, and he said everything looked fine, and it could possibly be “snapping popliteus” but never really gave an an actual diagnosis. I was at the beach last week, and it happened while walking along the shore, however after doing what I usually do, I didnt get that instantly releaving pop I usually do. I went to the er, and they did X-rays, and diagnosed it as a bad sprain, but I still can’t straighten my leg because it feels like something on the outside of my knee wants to move. I can’t get into an orthopedic for 3 weeks because they are so sparce around my area. Should I be worried? Is there anything else I can be doing?

    • Sorry to hear that Greg…
      Yes, a snapping popliteus can cause these symptoms… so can a bucket handle tear ( they may not always show on MRI).
      There are other less common reasons too. Sometimes rotating the foot outward or inward (with the knee bent to 90) — and then extending the knee can free up the tendon. OTherwise you will need to wait until you can see a doc again and perhaps go through some repeat tests.
      Good luck

  • I was injured June 8th and was diagnosed with a complete acl tear and two mcl small tears. It took until August 4th to get operated on. The original acl had cyclopsed and restricted my knee from extending. This was removed and a patellar reconstruction done. I am in physical therapy but am concerned if my leg will straighten back out. I am religious on my at home exercises. Is there any extra exercises that may help to specifically straighten out this joint? Maybe I am a little impatient for results to happen. Any time lines where I may see improvement in straightening the joint. I swell at my ankle after physical therapy and extended time on my leg.

    • Assuming the ACL recon went well and the tunnels they drilled are in a good location then you should be able to gain back extension.
      Good luck

  • Hi doc, I am a cheerleader an am experiencing knee pain. I was back-spotting a stunt when my flyer came down and hit my knee cap. I felt a pop and then another, my knee started bruising and swelling immediately. It has been about two days now and my knee is still painful to the touch, swollen, bruised and I am unable to straighten it. Could this be a severe injury? I have looked many things up and it says it may have been a subluxation or meniscal tear. I have had surgery on this knee a few years ago for a meniscus tear, but the pain isn’t the same. Should I be worried?

  • Hi, I hurt my knee playing basketball a couple of days ago. It’s extremely painful to straighten it and I can only walk on crutches or on my toes (for short duration). Yesterday, I went to the urgent care clinic where they did an XRay (knee bones looked good) and advised raising it, ice and compression. Curious at what point should I go to get an MRI if I’m still experiencing pain or lack of improvement? Thanks.

    • If a knee can not straighten after an injury we usually try to MRI the knee within the first few days to weeks.
      Good luck !

  • Hi! I have been training and running quite a bit and completed my Spartan trifecta. But with all the running I was doing, my knee is a little messed. I never actually had a point where I thought I’d hurt my knee and didn’t ever feel like something tore or popped. I have been walking around with it not straightened all the way. It can straighten and does every once in a while but when it does I’m scared something is going to rip or pop. When I Ben my knee it is very tight and after running 4 miles the other day there is a little swelling, is very tight when I bend it and won’t straighten unless forced. Any suggestions?

    • Fairly common complaints in a runner. The swelling is giving you the feeling of tightness.
      The swelling and pain could be coming from a mildly arthritic knee and / or a degenerative meniscus tear (very common in runners- even those without pain). These knees can sometimes take a few months to calm down entirely. Certainly if it lasts more than a few weeks, or worsens I would have a doc at least examine you and perhaps check on xray. Keep in mind that stress fractures are not common, but certainly on the list of possibilities. If walking continues to cause discomfort, then an examination is indicated sooner rather than later.

  • Hi! I am a high level competitive soccer player and I was trucker on the dislike from a defender. At first I didn’t feel it but soon after being hit, I couldn’t really sprint as fast as I am capable of and I cannot straighten it out after many hours of biofreeze and rolling out my knee? Is this something to just ice and leave it be or does this sound serious?? Thanks.

    • HI … Following a knee injury, swelling and loss of extension usually mean that the knee should be examined. Sometimes the loss of extension is due to a ligament strain… but sometimes it means there is a bucket handle or large meniscus tear.

  • Hi, I injured my knee 04-17 – twisted it and could not fully straighten, extreme pain . Diagnosed with complex lateral meniscal tear. Op in Aug 17 – removed remainder of meniscus, diagnosed with Grade 3/4 osteoarthritis in rest of knee. Still cannot straighten knee after months of physio. Had injection for the pain and now also trying acupuncture. My ortho says cannot do anything about it due to my age (54!!) and will have to live with it!
    Walking with constant limp and now pain in opposite hip, leg and ankle. Physio has said maybe i should ask for a second opinion as she feels i need a TKR? My surgeon will not entertain the idea! Help!!

  • I was playing soccer and i went to chest the ball in the air and came down on one knee i hear a few pops all in one second and couldn’t move it for a good 10 min and my friends carried me off and then it’s been about a week now and is still swollen on the inside of the left knee and i can’t make my leg a 90 degree angle

    • Sounds like you need to see a Sports Doc for a good examination.
      Good luck to you !

  • Hello,
    yesterday i was on a step stool putting things on top of the refridgerator. When i stepped down my knee felt funny like something is out of place. Felt that way the rest of the night. No pain or swelling. When i got up this morning my knee wont straighten without pain and its uncomfortable. A little swelling but not very much. Should i go to the doctor?

    • Hi Laura… surprisingly, many degenerative meniscus tears can act up after no obvious trauma… Often times your symptoms will subside and improve over 7-10 days, or longer in some instances. Most of these tears (which are incredibly common in people over 50) do not need surgery. So, hopefully your symptoms improve over the next few days. If they do not, then consider seeing your doctor.

      Good Luck

    • Hi, I’ve had a history of rupturing my ACL. There are times after years of the injury where I popped my knee during sports though I’ve relocated “it” everytime myself to be able to straighten my leg with no swelling after. What could possibly be shifted during the popping?

  • July 2016 I twisted my knee at work went on workmans comp. They did exray and said it was just arthritis. I went and got a mri and found out it was a mencus tear. I cant straighten my knee hd surgery and still can’t straighten my knee. How long will it take me to straighten my knee. Its already been 3 months

    • If the Xray showed arthritis then the meniscus tear likely wasn’t what was bothering you. Osteoarthritis takes precedent. It is capable of limiting motion, and causing severe pain.

  • My 2years old daughter underwent knee surgery for cause of septic arthritis, know we can straighten her leg when she is sleeping but she will walk with bent leg and she can’t bend her knees fully even after 5 months

    • I’m sorry to hear that :-(. It’s a little too complicated to handle something like this in this forum. What does your surgeon say? Have there been repeat xrays recently? Those knees often require serial xrays. Those are many xrays over time to see if any degeneration of the cartilage too place. An MRI might, repeat might be useful too… since a 2 yo knee has more cartilage than bone. But an MRI in a 2 yo is a big deal since they will need sedation. Talk with your surgeon… perhaps they will think that physical therapy is worthwhile. If the knee is still swollen then a repeat aspiration (taking fluid out to test it) might be indicated too. Like I said… very complicated… might just need PT and time… might need to be investigated further. Depends on the exam and severity of initial infection, type of bacteria, etc. Talking to your surgeon, or a second opinion will be far more useful.

  • My knee does not hurt but I can’t make it go straight. I did not hear any pops of any sort when this started. When I try to straighten my knee it feels like if my muscles are getting streched so I can’t extend it all the way. Any suggestions on what to do before I see a doctor?

    • Sounds like you should see a doctor first for some guidance. At least a good exam and perhaps a set of xrays.
      Good luck

  • Hi Dr. Howard,

    I jumped and landed strangely, heard a pop and hurt my knee. Hobbled off the soccer field and immediately iced. Xrays came back normal, still waiting on an MRI. I can squat and rotate just fine, I have just noticed a bit of swelling around my knee (left knee, medial), and can only extend to about 95% of the way (it starts to hurt). The doc says I have a bucket handle meniscus tear that needs surgery. He’s scheduling an MRI to confirm.

    Do you think it is possible that my knee is just swollen, and that this is causing the stiffness? other than not being able to fully extend, I can squat, twist, etc.


    • Hi Stephanie … I’m sorry to hear you have injured your knee!
      Usually a good exam can tell what is wrong. Hopefully the ACL is OK … your patella or kneecap is stable, and this is just because of swelling.
      But since i haven’t examined you I can’t give you much more than our most heartfelt wishes that all is well and that you have a speedy recovery.

    • Did you end up having surgery or did the knee recover with therapy? I have very similar symptoms.

  • Hi I have been having subtle knee pain for about the past year. It often acts up when i do physical activity. It also often pops a lot. This morning I could barely put any weight on it and I could not straighten it. It felt like there was a ton of pressure in my knee cap. And I couldn’t move it because of the pain. This evening I tried moving it and it popped really loudly. It is still sore but it now feels like all the pressure it relieved and it feels a lot less painful. Do you have any ideas? Thanks for your time

    • Common story Lucy. I am glad that it feels better! This is often how an arthritic knee behaves, especially if there is arthritis underneath your kneecap or patella. Best to see a doctor, and have an xray to be sure.

  • Great article, Howard. When I was a young man and blew out my rt knee after getting tangled up with a defender on a fast break, the entire gym heard it snap and me howling for what seemed to be a long time.
    I couldnt straighten the knee for 4 months after the cast came off. Diagnosis back then was a bucket handle tear and lcl tear. my conservative ortho surgeon opted for 9 months in a cast with minimal progressive weight bearing with 3 months of torturous PT to follow.
    After 4 years, the instability lessened significantly despite my continuing to play ball. The initial arthogram somehow missed the MCL and ACL tears but, here i am 40 yrs later still running, biking and playing tennis, thankful for the conservative approach initially taken and a large dose of good fortune that the knee is still holding together. I appreciate every workout, race, and match knowing im on borrowed time.
    Never underestimate how one’s body can adapt regardless of the injury.

  • Hey!
    I am about 1 year post op on the ACL tear using Patellar Tendon graft. I cannot fully hyperextend my operated knee as much as my other knee. When I try to stand on my operated leg (full weight) and fully extend it/straighten it, I feel pain. Is this considered normal and most likely go away over the next year? Or is this pain an indication that there is something off on the recovery? Please note that I have been really on top of my rehab – I just still have pain when I try to fully straighten the leg.
    Thank you!

    • Hi ..
      If you have a loss of extension this far out from surgery and if you have pain at full extension it might be worth discussing whether or not your doctor feels you have a cyclops lesion. A cyclops lesion is a ball of scar that can develop in the front of the knee after ACL surgery. It can block extension and cause pain. There are other causes of loss of extension… They include where the tibial bone tunnel was placed. When knees hyperextend we need to keep that tunnel back far enough to prevent loss of extension after surgery.

  • Hi Howard!
    I am just looking for some info and hoping you have seen this before. I am 2 months post op ACL reconstruction with quad tendon graft. minor 10-20 percent meniscus tear that was repaired. I cannot extend my knee past 3-6 degrees depending on the day. I cannot bend my knee past 90 degrees pain limiting. And my knee aches pretty much all the time. My xray with the graft sites and tunneling looks great and my MRI shows some scarring, but not a cyclops lesion or anything like that. Have you seen this before and if so what sort of interventions were successful? I am not finding a lot of literature on successes after these types of ROM issues.
    Thank you for your time! Kilie

    • Yes… every year we see a few people who become tighter and stiffer than others. Assuming the tunnels are in their normal position, you have to keep at it. Sometimes we talk to patients about a manipulation under anesthesia, but as long as you see an improvement every week, even if it’s just a little, most of these stiff folks end up doing fine. It will simply take nearly a year to get there.

  • Hi I have two ripped meniscus and they both lock up the same time and feels like I’m not going to be able to walk every day I go through this tremendous pain of my knees locking up .im scared that in ten years I will be in a wheel chair it’s so painful I cannot have surgery because I have had 42 blood clots due to protein c diffency I have .im not allowed to be taken off my blood thinners because I cot fast I had mri showed a lot of stuff floating around and both ripped meniscus.im not allowed any injections either or nsaids.I am in severe pain I cry every day due to this not only that I have back problems as well that I need surgery but can’t due to the protein c diffency ,please any suggestions would be greatly appreciated thank you Connie

    • HI Connie…
      You need to talk to your hematologist. They can often find a “bridging” technique of anticoagulation that can allow you to have surgery if it is needed. Once you develop a strategic plan with a hematologist then you can speak with an orthopedic surgeon.

  • Hi, i would so appreciate advise on whom to consult. My 13 year old son fell off his scooter a few weeks ago and landed on his knee. It urt, but didn’t swell or bruise. We found out a week or so later that although his leg can be straightened by putting it flat, he cannot straighten the leg by using his muscles (when sitting on a chair or the floor).
    Thanks very much for your feedback.

    • I would consider a good exam, and probably an X-ray to start. You need to be sure he doesn’t have a mechanical issue with his “extensor mechanism”. That’s the quad tendon-patella-patella tendon-tibial tubercle.

  • I had torn my ACL and meniscus in March 2019. It took weeks to see a surgeon so I didn’t have my surgery for another 4 weeks. My meniscus locked up my knee so I couldn’t walk at all during that time. I had an MUA in July and a scope to remove scar tissue in October and I still can’t get full extension. Flexion is actually better thouh. I do PT every week, do exercises daily… nothing is helping. I’m only 25 so I doubt a replacement will be even considered but do I have any more options?

  • Hi, so I was playing basketball and I jumped pretty high to get the ball, whilst in the air I felt something with my knee and when I landed my knee was hurting bad, my knee joints were stiff at first, but now I can walk, my knee has swollen and I dont know what’s happening. The swollen part of my knee doesn’t hurt that much but the side of my knee that muscle over there hurts pretty bad when I move my leg

  • My 11 year old son fell off his bike and landed on his knee. It hurt for a little while and then went away but he limps when he walks. He says it hurts to straighten it and put his full weight on it. It is not bruised or swollen. In fact I am able to put pressure and his knee and the surrounding area with no soreness. I am wondering if his knee just needs time to heal or if there is something seriously wrong. It’s been about 4 days. I am embarrassed to say that we have no medical insurance and I am a single mom so there is no extra money laying around for a Doctors visit. Am think of taking him to an ER or something but want to make sure I am not over reacting or incurring an unnecessary cost.

    • Please don’t be embarrassed… we as a country should be embarrassed that we have people who are uninsured.
      If your child still cannot fully straighten the knee and put weight on it then you should have him see someone.

  • I was playing basketball a few weeks ago and felt something in my knee pop out of place. It popped back in pretty quickly and I was able to continue playing. It happened two more times after this first time and I was able to pop it back in when I would straighten my leg out completely. It just happened again today and the pain is too much to straighten my leg and pop it back into place. At this point, I feel like I should go see someone. Does it sound like a tear of some ligament?

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