Simply put, if you are unable to straighten your knee after an injury, you may have a severe knee injury. Even mild injuries can result in loss of full motion and pain when trying to straighten your knee. How do we tell whether your knee injury is mild or severe? In general, if you lose the ability to fully straighten your knee you may have a severe or serious knee injury and should see a doctor.
Why can’t I straighten my knee?
Knee injuries often occur after a twisting injury or a direct contact injury. As an athlete, we learn to shake off many knee injuries. After an injury, most of you will wonder if your damage is serious or perhaps just a simple knee strain. Those of you without a known injury, but with a history of knee osteoarthritis might also lose the ability to straighten your knee.
Pain when trying to straighten the knee is common. In general, as specialists, we look for two different situations. One where you cannot straighten your knee because you feel that something is stuck inside the knee and blocking you. The second is someone who injured themselves and can get the knee fully extended, and has severe pain and swelling when trying to straighten the knee.
Below we dive deeper into the causes of pain when trying to straighten your knee. Also discussed below are the five most common problems that make it difficult to straighten your knee.
When should I see a doctor?
How do you determine if you have a serious knee injury? If you hurt your knee twisting it, or if you were struck by someone else and you have pain trying to straighten it, you may have a serious knee injury. But you may not. There is a difference between someone with pain trying to straighten the knee, and someone who simply can’t straighten the knee because they feel like something is blocking their motion.
It turns out that if you lose the ability to straighten the knee fully, or you can not straighten the knee without pain then the risk of having a serious injury increases. Less worrisome are people who simply woke up and now have pain trying to straighten the knee. Often times that might be some inflammation or swelling and is often due to some underlying osteoarthritis.
Determining if you have a severe knee injury is important. After most mild knee injuries we are back on the field fairly quickly. If after a few days you cannot straighten your knee without pain then you cannot return to the playing field. Basically, if your loss of extension (straightening the knee) persists for more than a few days you should see a doctor for an evaluation.
As we discussed in this post, sports medicine doctors consider the loss of being able to straighten the knee one of the signs of a serious knee injury.
A bucket handle tear of the meniscus is one of the most common reasons why you will find it impossible to straighten your knee. We have a post dedicated to this unique meniscus tear here.
If you can’t straighten your knee, you probably have a severe knee injury
After an injury, there are a few different reasons why you might not be able to straighten your knee. Often you can’t straighten the knee simply because of pain and swelling. In cases where you can not straighten the knee because of swelling, you will notice that your ability to move the knee improves as the swelling goes down. Besides, when you have lost the ability to straighten your knee because of swelling, you do not usually feel as if something is stuck inside the knee and blocking your movement. In serious knee injuries, you will often feel as if something is blocking your ability to straighten your leg or your knee feels locked and it is not able to move freely.
Here is a list of knee injuries that can make it difficult to straighten your knee.
5 Common Reasons Why You Can’t Straighten Your Knee?
- Meniscus tear. Specifically a bucket handle tear of the meniscus. This is a unique tear where the torn piece of meniscus flips into the center of the knee joint.
This torn piece then locks your knee and prevents it from straightening. If you have a bucket handle tear of the meniscus, you will find it impossible to straighten your knee completely. These tears can be repaired or sutured back into place. The sooner they are repaired, the better the chance that the tear will heal well. It’s not an emergency, but you should see someone sooner rather than later.
With a bucket handle tear, you will usually feel as if something is caught in the knee and preventing it from straightening. That’s because the meniscus has flipped over and is sitting in the middle of the knee joint preventing it from fully straightening. You will also have severe pain when trying to straighten a knee with a bucket handle tear.
Most bucket handle tears will require surgery to put the torn piece back into position and sew it back into place. The torn portion often requires a repair so that it has a chance to heal. The success rate of fixing a bucket handle tear is very high.
- ACL tear. If you had a twisting injury and felt a pop, there is nearly a 75 % chance that your injured your ACL. Many athletes with an ACL tear will find it painful to straighten the knee. The knee isn’t locked, but it hurts too much to straighten it out.
Within a few days of tearing your ACL, the swelling will start to diminish, and you will likely be able to straighten your knee. Sometimes athletes who tear their ACL will also rip the meniscus too. This is another reason why it might be hard to straighten the knee.
If you twisted your knee and felt a pop, then you noticed that you could not straighten your knee you should see a Sports Medicine Physician. Your next steps if you think you have an ACL tear are discussed here.
- MCL Injuries. MCL or medial collateral ligament tears in the knee hurt. They hurt a lot. That pain will be on the inner or medial side of the knee. An MCL tear can be mild or severe. The ligament can be stretched or completely torn. Both situations will cause severe pain, so the pain level doesn’t correlate with how severe the injury is. We wrote about MCL injuries in this post. Most MCL tears do not require surgery, some may require a brace. MCL injuries often hurt a lot so they prevent you from being able to straighten the knee without pain.
- Swelling. There are many reasons why your knee might be swollen. We explore the common causes of knee swelling here. Swelling is common after severe injuries due to bleeding. That can cause enough inflammation and pain that straightening the knee is just too painful. Bleeding can occur due to a meniscus tear, ACL tear or MCL tear.
Knee swelling can also occur without an injury. People with osteoarthritis can develop swelling due to inflammation. People with gout or Lyme Disease can also develop significant swelling. If the swelling is severe enough, you will lose the ability to straighten your knee. You should work with your doctor to find out why your knee is swollen.
- Patella or kneecap dislocations: Patella dislocations are far more common than previously thought. If you felt or heard a loud clunk or pop in the front of your knee while turning or you were struck in the front of your knee then it is possible that your kneecap came out of place and went back into place on its own.
We call this a spontaneously reduced patella dislocation. Many people who dislocate their kneecap will develop significant swelling due to bleeding inside the joint. After a patella dislocation, you will find it difficult to straighten the knee due to pain. This post on patella dislocations goes into far more detail.
- Tendon Injuries: Some people can not straighten their knees due to weakness or tendon injury. Injuries to the quadriceps or patella tendons will affect your ability to straighten the knee. If one of those two strong tendons are torn, then you will not be able to straighten your knee. If you ripped your patella tendon or your quadriceps tendon, then you physically will not be able to straighten the knee. That is because the muscles which allow you to straighten the knee are no longer attached to your kneecap. That is why people who tear their patella tendons notice significant weakness. Patella tendon and quadriceps tendon injuries are more common in professional sports and adult weekend warriors. These are very rare injuries in high school and collegiate sports. Tears of the patella or quadriceps tendon will always require surgery to repair them. The patella or quadriceps tendon will need to be reattached and sutured to the patella.
If you have suffered an injury to your knee and you are unable to straighten it, then there is a good chance that you have sustained a severe knee injury. If you can’t straighten the knee fully, or cannot straighten the knee without pain, then you should consider seeing a Sports Medicine doc sooner rather than later.
Macayla
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?
Howard J. Luks, MD
It can be a severe injury. I would read this post on patella dislocations… and I would go see an Orthopedic Surgeon who specializes in patella dislocations.
Neil O'Malley
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.
Howard J. Luks, MD
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 !
Kendra
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?
Howard J. Luks, MD
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.
Graycen Rasmussen
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.
Howard J. Luks, MD
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.
Jackie
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!!
Thanks
Howard J. Luks, MD
Sounds like a second opinion is needed.