7 signs your knee injury could be serious

Knee injuries are among the most common injuries in sports and exercise. Fortunately, among the patients I see in the office, most knee injuries do not require surgery.

If you suffer a knee injury, how can you know if it is serious and worth seeing an orthopaedic surgeon? This list is far from comprehensive, but here are seven signs you have a knee injury that might require surgery.

It goes without saying that the information in this post, like all of my content on this blog, on my podcast, and in social media, is not intended to provide specific medical advice. Please consult your doctor for any medical concerns.

Your knee is swollen.

It might not be a big deal for your knee to have a small amount of fluid present. On the other hand, if your knee swells up like a basketball in the first few hours after an injury, you could have an ACL tear or fracture.

You heard a pop.

I don’t mean a small pop like the one you feel when you crack your knuckles. I’m also not talking about the popping many of you feel under your kneecaps normally with knee motion. If you hear or feel a loud, painful pop during an awkward landing or when you get hit in the knee, you could have torn a ligament. Many athletes say that their teammates heard the pop when they tore their ACLs.

You can’t bear weight.

Knee injury in soccerExtreme pain trying to walk is somewhat of a generic complaint. Many injuries can be serious enough to cause pain when you try to put pressure on the injured leg. It is still a sign you might consider seeking medical attention.

Your knee buckled or gave way.

If your knee buckled when you landed from a jump or changed direction suddenly, you could have suffered ligament damage, such as an ACL tear. Alternatively, if you experience your knee giving out with twisting or landing movements in sports weeks or months after an injury, you should consider seeing a sports medicine doctor. True knee instability with activities can risk further damage to the meniscus or articular cartilage.

Your knee is locked.

Younger athletes can often tear the meniscus in such away that the inner, torn fragment can flip into the center of the knee and block motion. These bucket-handle meniscus tears often require surgery. The surgeon must push the meniscus back into place and repair it with sutures or anchors. Milder or more chronic forms of knee locking or catching also can suggest you have a meniscus tear.

You cannot fully extend the knee.

Pain, swelling, and inflammation after acute injuries can all make knee range of motion difficult. If a patient comes to my office days after an injury and I can’t straighten the knee, I get at least a little concerned. It can be a nonspecific finding, though. Regardless, I have often found ACL tears, acute meniscus tears, patellar dislocations, and more in these circumstances.

Your knee hurts in a very specific location.

Patients with meniscus tears usually complain of pain in a very specific spot along the joint line rather than throughout the knee. Medial meniscus tears often hurt along the medial (inside) and posterior (back) side of the knee. Lateral meniscus tears often cause pain along the lateral (outside) and posterior aspect of the knee. Likewise, stress fractures usually cause localized pain on the bone at the site of the fracture.

I hope that this list is helpful. Again, it is not comprehensive and not intended to replace the advice of your doctor. If anything, I hope you would consider seeing your doctor sooner after injury if you have any of these complaints.

Sports medicine professionals – athletic trainers, physical therapists, and orthopaedic surgeons – are there any other findings you would add?

63 Responses to 7 signs your knee injury could be serious

    • I have had knee pains and IT band problems in both to left and right for over a year. Physical therapy helped after 4 months then the same pains came back. I also recieved cortisone shots in both and that did not do anything at all. Through an MRI my ortho doctor said I was born with a crack in my left knee cap and the bottoms of my knees that cause loud cracking are rough but he said nothing was wrong???? Is this something I should be concerned about? And what can I do I have pretty constant pain and am in the military so I am extremely worried please email me back as soon as you can. Thanks

      • I can’t really offer you too much advice without being involved in your care. Generally we don’t worry as much about popping in the knee, as many people have it despite having no pain. It can also be a sign of arthritis changes under the kneecap, and there aren’t easy treatments for that. You could discuss options for your pain with your orthopaedic surgeon.

  1. I was diagnosed with a sprained knee never got better had an MRI the day after I felt a pop and very painful

  2. Hello,
    I severely dislocated my knee cap six weeks ago. I have been walking on it for two weeks and making huge progress. However, I am not able to completely straighten my leg. The MRI showed no meniscus/ACL issue. I am in physical therapy however my leg just won’t straighten. What could this possibly be? I am very concerned and worried.

    • Without being involved and examining you, I can’t say if there is some mechanical block to extension, like a meniscal tear. Generally though, the lack of full extension of the knee could be serious. An orthopaedic surgeon can perform an exam and order an MRI if needed to find the problem.

  3. A day ago i was running and i fell right on my knee iits red and i can bearly straighten my knee and im just laying doown its really hurting for no reason i can even reall walk right

  4. I am going to try to summarize. A ski injury created partial tears in all ligaments in my right knee except meniscus. Had a mri and determined to be an extreme knee injury by an orthopedic surgeon Fast forward several years and I now get short periodic pain and failure to be able to fully extend leg. This pain is severe and last less then a day until I feel a pop or release. Immediately there is total relief of pain and a knee that is as normal as can be.
    I still ski, golf, hike and bike on a regular basis. Hard to get examined because it disappears.
    your best guess?

    • Without really being able to examine you and determine where in your knee the pop was coming from, I’m not sure I can point you in any particular direction. Sorry!

  5. In 2011 i triped and fell whilst out running on a pavent stone,and went down on my right knee,i went to the hospital they xrayed it and said there was nothing wrong with it,just bruised,Well several weeks later i was in the shower,and found when i put hot water on my left leg below knee i could feel it,But when i did the right it was totally knumb,I then got severe back ache and the hospital did a mri scan,to find my l3 l4 nerves were trapped in my spine,since 2011 ive had an operation on my spine and an operation on my knee,Could you tell me would this be the result of me falling and landing on my knee in 2011,at that time i was 52,im now 55,and disabled,need to wear knee brace without knee collapes,thank you,neil horne,huddersfield,uk.

    • I can’t say without examining you and looking at x-rays and an MRI. A patient with buckling or giving way of the knee might consider seeing an orthopaedic surgeon to see if any ligamentous injury exists.

  6. A person twisted my leg the wrong direction and my knee popped out I have had x ray and everything is still in tact but for the life of me I cannot bend my leg can’t force it either with hand what could be up with that?

    • Without examining you, I can’t really say. It is possible for a patient to have a mechanical block to motion (such as a loose body). An orthopaedic surgeon could deteremine if one exists and what it could be.

  7. long history with left knee…
    Medial tibial plateau fracture 7 years ago (I was 32 at the time), Schatzker 4 variant w/popliteal involvement. Several surgeries later, including fem-pop bypass & lateral uni-compartmental knee replacement.
    fast forward to current – we moved out of state, and can’t find an orthopedic surgeon to take my case (0 for 5). I’m “too high risk” because of the bypass, and I’m “too young” for even the uni-replacement – let alone consider doing anything further.
    The medial side of knee joint hurts sharply with any weight bearing, and I particularly can’t straighten it while standing/walking. It sorta feels like I’m culturing a pearl in there (If I had to imagine what an oyster goes through!), and it feels like my kneecap is grinding against sandpaper.
    Can’t feel anything on the lateral side – but then again, I have a hunk of metal on that side from the uni.

    ..without examining, of course, is this something that I simply have to live with? or should I start throwing darts at the orthopedic section phone book again?

    • I understand your frustration, but without being able to examine your knee and review studies, I can’t give you any specific answers to your questions. You might try the AOSSM website and use its Find a Doctor tool to find an orthopaedic surgeon in your area.

  8. I have had a history with my left knee, however at volleyball I jumped and heard and felt 2 pops, painful but I continued to play as I tolerate pain well. What are your suggestions?
    Please and thanks

  9. hi my name is adelaide burling i am 22 year old and i have a most common left knee injury and what happen was that i did my acl and i buckled my postier ligament it gotten to the point where i have joint effusion and plus the swelling of my left knee as been increasing and i have not been able to been able to get a opporation done yet due to western health footscray hospital recieptionist said to me it could weeks or longer so i had no choice and when it was july i found that i am pregnant and plus it stuffed up my chances of having my left knee injury done so i have to wait until the baby comes by next year though .

  10. i have popped my knee several time before. Like 5 by now. I had physical therepy and it helped, but it stayed in a weird position, a little turned the right than usual. It began to hurt so much i began to massage it and then i pushed the bottom part in by accident. It felt releiving for a moment but then it got swollen and it hurts worse now, also i feel something wants to pop out lately. I am really, really, really, scared, actually terrified, and incredibly worried .

  11. i want to stand and my knee pop i hadto sit right down it was instant paini took pain meds and used a hot pack then an ice pack it stop hurtin a bit but it hurts when i stad or try to move it a certain way i had a little swelling i can move it side to side without paind and i almost straighten it all the way out but it hurts when do what should i do next?

  12. I hurt my knee 2 yr ago and they said i had a strained mcl and acl and needed physical therapy i was supposed to do 3 or 4 weeks and only completed 1 now i can’t run at all and the other day i got hit by go kart and now my knee hurts to walk on and locks up what should i do

    • If a loose flap or piece of articular cartilage broke away, partially or completely, it could catch between the femur and tibia with range of motion.

  13. I got a knee injury last Saturday. I was riding a long board and I tried to get off my foot went into a curb and my left knee twisted to the left and I heard a loud pop. After going to the er they couldn’t tell with an x-ray so they sent me to the orthopedics. Thin is the ortho kept talking over me. I didn’t get to tell him I can’t bend my knee. I can almost straighten it but I can’t bend it into a sitting position. Any ideas what it might be?

    • I can’t tell you in your case specifically. Lack of flexion early after a knee injury can be related to swelling within the joint. It can also be caused by some block to motion, like a meniscus tear or loose piece of articular cartilage.

  14. I had no injury what so ever, had bad knees since i was 11.

    last week my keft knee started feeling uncomfortable to walk on, and everyday since then has gotten worse, now 11 days after still getting worse(Pain started day 9 followed by cracking) . The 7th day got a mri and the conclusion of my results:

    - Abnormal Patellar and Trochlear Morphology and Patellar Malalignment.
    - Grade 3 Chondromalacia Patellae.
    - Infrapatellar Fat Pad Impingement.
    - Joint Effusion with Synovitis.

    Im seeing the surgeon tomorrow as apprantly i need surgery this week before i end up crippled.(im only 23)

    i was originally seeing him for my right knee as ive had multiple dislocations on my R knee for the past 10 years and only in the past 7 months, ive had daily dislocations everytime i walk, so not sure if that would have anything to do with my left knee.

    (So, now im having surgery on my left knee, Then my right knee.)

    So my Question is, do you have any opionions on this?

    Thank You

    • I can’t really say too much without examining you and looking at your studies, so your orthopaedic surgeon should be able to help more. Patellar instability, especially when caused by bony abnormalities of the femur, can be a tricky problem and often requires extensive surgical procedures.

  15. I landed heavily straight on my knee whilst playing futsal. Immediately felt pain and that it wasn’t aligned correctly. It felt as though my foot was facing out more. Hobbled to the bench where I then tried to find out what was wrong. Can’t bend my leg back sometimes as is locking up. And hurt a lot that night when rolling over in bed with the twisting motion. I can straighten it and put weight on it to walk. Am going to a doctor today but interested to know your thoughts with what it might or might not be.

    • It’s hard for me to say without examining your knee. Inability to straighten the knee or bear weight are some of the signs for a potentially serious knee injury.

  16. I’ve never had an injury to either one of my knees. However, I do have severe neuropathy. I am unable to bed either one of my legs to walk. It’s like having two baseball bats attached at the hip. I’ve had a CT of the spine which showed a herniated disc at T8-T9 as well as an EMG which just showed that I have neuropathy. I have seen 5 different neurologists and none of them have ever seen “postured” legs like mine that just won’t bend. I am able to bend my legs to sit, but thats about it. My calf muscles are always tight, they never relax… they are always contacted. Any advice you have.. Im all ears! Thanks a lot

  17. I twisted on my knee when getting up after sitting on the floor. I now cannot extend my knee fully and have pain in my calf when trying to do so, I can walk pain free on a slightly bent knee. This happened today should I seek help or rest and pain killerss
    Thank you

    • I can’t tell you what to do. Generally I think seeing an orthopaedic surgeon for a knee injury that is not improving is a good idea for many people.

  18. I was playing soccer about 2 months ago when I twisted my left knee funny. I couldn’t straighten it out fully for about 5 days then I could but it still hurt. It hurt mildly sometimes then I went sleding and stacked it and after I stopped tumbling my knee hurt like really bad. It hurt around the front/lateral side and is extremely painful if I put weight on the sides of my knee. I get sharp pain and then constant pain. There is thus thing that clicks if u rub your finger on it above/beside my knee cap on the lateral side which wasn’t there before. It has been two weeks now and it us no better. What do u think it is

    • I really can’t say without examining it/you. You might consider seeing an orthopaedic surgeon if you still have trouble weeks out from the injury.

  19. My sister who is 14 has a history of knee problems and in July her knee locked up and doctors at the time thought that she had torn the meniscus in her right leg even though they did not carry ANY x-rays or MRI scans. Nearly 3 months on she still can’t put any weight on the leg even though she’s been receiving hydrotherapy and physio and is in a lot of pain. I’d be interested to know your thoughts

    • I don’t know that I can shed much light on it without being involved as her doctor. X-rays and MRI can demonstrate structural damage after an episode of knee locking.

  20. I was playing basketball two days ago I jumped up and landed on my leg fully extended locked and I felt inward pressure to my knee when I landed and imidiatly fell to ground and felt a lot of paint waited a few minutes and started to play again. My knee didn’t get swollen but have small pain when I extend leg and try to lock it in place. My question is what kind of damage can be cause to the knee when lading on it like that?

    • A knee injury suffered by landing on the foot with the knee fully extended can cause a number of different structures to be damaged, such as the ACL, one or both of the menisci, and the articular cartilage.

  21. Three days ago I was hit in the knee it hurt really bad at the moment I played the rest of the football game in discomfort. It swelled upright bellow the knee cap to the left. It hut for 2 days really bad but now it is better and doesn’t hurt much unless I’m sitting and not moving. What do you think

    • I can’t give you specific information. Generally if an athlete or active person improves within a few days, he or she can observe it and try to return to activities and see how the knee does.

  22. this rail or something hit my leg and on this specific side it hurts and when i poke on the right side of my knee some thing on the left side moves what should i do

  23. Hi Dr David,

    I had a fall a week ago. My weight is around 100kg and I’m standing on 176m tall. I fall on my left knee. I was scared that it got something to do with my bone. But on my referral letter to see orthopaedic stated my diagnosis with Contusion of Left Knee. Yes I did has bruised on my knee. I started with walking with crutches. And now I can walk without crutches. But my concern and fear is, I am still scared to bear weight on my left knee. As I felt loosen on my joint.I don’t feel pain. I am just scared if my knee able to bear my weight if I press and walk like normal. What is your opinion?

    I appreciate your assistance.

    Thank You

    • I can’t really say, but the orthopedic surgeon can tell you whether weight bearing is safe. Generally for simple walking, I don’t restrict a patient from bearing weight unless it causes significant pain or causes the knee to lock, catch or give way. But again, it depends on the nature of the injury.

  24. I feel on my left knee with all my weight back on January 17th and cant seem to get a straight answer of what is wrong and why its not getting better almost 10 months later. Ive had an xray and mri done and both showed normal. I’ve seen my normal doctor multiple times and no help, ive seen a knee orthopedic and they said I have runners knee and to do physical therapy and wear a knee brace both of which did not help the brace actually made it worse, the pain has gotten so bad that I went to the er because nothing is taking the pain away nor am I sleeping very well. The er doctor looked over both the xray and mri from January and saw nothing wrong and no runners knee either. He said that the pain I’m having sounds like a torn miniscus but that its boy since the mri was normal. My entire leg hurts it burns, stabbing pains, tearing pains, and sharp pains but no one can seem to help me. I feel like its going to have to get to where I cant walk on it at all before someone will help.

    • Jessica, that does sound frustrating. Meniscus tears almost always show up on an MRI. Without being involved, I don’t think I can give you too much information on particular injuries or their treatments. I hope you find an answer!

  25. Hey doc, I have some scary news. In two months I’m supposed to go out to Alberta to be a ski instructor and today I did something to my knee where it hurts to move up and down and I have pain when I fully outstretch it. I’m going to go see emerge right now, but I need to heal up in 2 months time. Please help me fulfill this goal! I’m very scared and I took a gap year so I could do this and now I’m injured!!!!! Please help me. Should I do stretching, ice, how often for both, nothing hurts when I poke anywhere around the injury which makes me even more scared.

    • I don’t know that I can help too much without knowing what the injury is. Your orthopedic surgeon can give you specific advice. Generally frequent ice and elevation to get the swelling of the knee down and working to regain full knee flexion and extension can be important in the first few days after a knee injury.

  26. hey the other day i hit a car fall off my bike and landed on my right knee. now left side of my right knee is swollen, now it hurt when i walk up the stair and down, and it hurt when i try to get up

  27. Hi Doc,last month playing softball I was taken out by my knee. I played the whole game in discomfort, but just thought it was badly bruised. It swelled up right away and had X-ray. Nothing was broke but still a month later I have a knot above my knee cap.I can walk on it, but it pops and I feel like there is air underneath my kneecap. I’m scheduled for an mri tomorrow my question is, will they be able to see if anything is torn or pulled (I have arthritis ) and if so will surgery be necessary??

    • Yes Lauren, an MRI can show injuries to the meniscus, tendons, cartilage, and ligaments in your knee to help your surgeon determine treatment options.

  28. My problem has now existed for about 3 months. I thought the pain would go away. Yes I one of those guys who try to tough things. Any how, my pain is located on my right knee, specifically on the inside left (top part inside left towards knee cap but not on the knee cap) I can not run, it is uncomfortable to walk an distance and I can balance or stand on the rich leg in a locked position without extreme pain and the knee giving way. I am headed in this week to have it looked at. Any initial thoughts or gut instinct thoughts?


    • I can’t say too much without examining you, but your orthopedic surgeon should be able to determine a cause. There are many structures on the medial side (inside) of the knee that can cause pain in that area – meniscus, MCL, hamstring tendons, patellar ligaments, plica, etc.

  29. wow…sorry for the typos in my question. Meant to say I ca not stand on my right knee in a locked position without extreme pain and the knee buckling.


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