Why You Can't Bend Your Knee Without Pain (13 Possible Reasons)

Why You Can't Bend Your Knee Without Pain (13 Possible Reasons)

Mobility is everything. Our world understands this concept now more than ever. When you cannot go where you want to go when you want to go, frustration sets in. When you can't bend your knee without pain, you quickly find yourself limited.

You may wonder, why can't you bend your knee without pain? Knee pain results from one of three problems. A sudden injury, an overuse injury, or disease can cause knee pain when bending. 

Keep reading to learn everything you need to know about what to do when you can't bend your knee without pain. 

How a Knee Works

To understand the potential problems with your knee and why it hurts when you bend it, you need to understand the joint itself. Biologists refer to the knee joint as a hinge joint. This means it can both bend and straighten. 

Here are the main parts of your knee and the ways they work together when you bend your knee: 

  • Muscles: You have three major muscles that work together for your knee to move. Your quadriceps (thigh muscle), hamstring (muscle behind your thigh), and calf (muscle on your lower leg) all work together. When you bend your knee, for example, your hamstrings contract and your quads relax. 
  • Bones: Your femur (thought bone), tibia (shin bone) and patella (knee cap) work together to make your knee bend. The patella sits in a groove in your femur, and the upper and lower leg bones will roll, glide, and spin around the patella. Your muscles control how those bones move. 
  • Cartilage: Your knee has cartilage in the knee cap, cushioning the bones so you have shock absorption. The meniscus is that cartilage. It is a spongy substance that moves with the movement of your upper and lower thigh bones. 
  • Ligaments and tendons: these are the stringy tissues that connect your bones to bones (ligaments) and bones to muscles (tendons). They stabilize your knee so it does not go crooked as you bend. They keep the knee joint in line with your hip and ankle. 

All of these parts work together to create a smooth, pain-free joint as you bend and straighten your leg. When any one of those parts malfunction due to a disease or injury or just basic wear-and-tear, you end up with a knee you cannot straighten or bend without pain. 

Reasons Why You Can't Bend Your Knee Without Pain

Pain is debilitating. It can prevent basic mobility. If you can’t bend your knee without pain, then you have one of three problems. 

You may have an injury, illness, or wear on your knee. Here are the major reasons why you may have knee pain when bending. 

1. Arthritis

Arthritis is an inflamed joint. Millions of people worldwide suffer from it. Knee pain when bending typically results from osteoarthritis. 

Osteoarthritis occurs when the cartilage lining your joints begin thin out due to wear and tear. Excessive friction causes bony lumps to form in the joint where your leg bones meet. 

Arthritis occurs because of a variety of reasons. If you've damaged your knee in the past or if you have a family history of arthritis, you're prone to the disease. Also, if you are overweight and change the way you walk because of that weight, you're prone to arthritis. 

When you have arthritis in your knee, the pain may begin in the morning or it may just happen after you've sat for a long time and try to bend your knee. Your pain may even cause your leg to stiffen, making bending even more difficult. Gentle movement can alleviate some pain, but if your actions cause repetitive bending, like taking stairs or constantly bending down, you will see your pain increase. 

Arthritis typically develops over time. The symptoms will come and go and worsen as time passes. Usually, arthritis affects people over the age of 65. 

2. Baker's Cyst

Baker's Cyst can result from arthritis. This type of cyst develops when the bursa in the back of your knee begins to swell. 

A Baker's Cyst occurs when extra fluid from your knee joint gathers collects into the bursa. The back of your knee swells, and your knee is stiff and sore. 

The excess fluid can develop as a result of arthritis. If you tear cartilage or have gout, excess fluid can gather. 

Your knee will stiffen up, and you will have difficulty both bending and straightening the knee. Activity will make the condition worse, and the rest will make it better. You will feel a slight bulge at the back of your knee, kind of like a water balloon. 

3. Osgood Schlatters

Osgood Schlatter's syndrome occurs on the other side of age. Whereas arthritis occurs when you've crossed over 65, Osgood Schlatter's results in knee pain when you're a teen. 

When teenagers feel pain when bending their knee, they could be experiencing this phenomenon that occurs as the result of bones growing more quickly than soft tissue. 

When your bones grow more quickly than your tendons or ligaments, your knee will ache. You will have more tension through the patellar tendon over your knee cap in particular. This tension then causes damage to underlying bones. 

Rest and time will alleviate the pain caused by Osgood Schlatters. Any kind of knee injury recovery will take time and rest, but if you're young and treat your knee right, it will last you a lifetime. 

4. Runner's Knee

Runner's knee can happen to anyone, not just a runner. Doctors will refer to the runner's knee as anterior knee pain or patellofemoral pain syndrome. 

When your knee cap moves and puts extra stress or friction on the underlying tissue as you bend or straighten your knee, then you may have runner's knee. Weak muscles can cause a runner's knee. Also, if you have odd biomechanics due to problems with foot arches or odd hip angles, you are prone to runner's knee. 

You'll know you have runner's knee when you have pain bending your knee. This is the most common symptom. The pain tends to be right at the front of your knee. 

Your pain can also occur whenever you need to bend or squat or when you first move your knee after sitting a while. You may also notice a grinding or grating noise whenever you attempt to bend or straighten your knee. 

Runner's knee develops gradually. 

5. Bursitis

When you have bursitis, you have inflamed bursa. The bursa act as you shock absorbers in your knee. The fluid-filled sacs absorb shock as you use your knee. 

When you have repetitive pressure on your knee or constant friction or if you ever fall or experience a blow to your knee, the bursa will become inflamed. You will have pain, and the doctor will diagnose you with bursitis. 

Bursitis can develop with time, or you can experience a quick onset of it. 

6. Housemaid's Knee

If you spend a lot of time kneeling, you may experience the housemaid's knee. With housemaid's knee, the bursa just beneath your knee cap swells and causes pain. This happens as the result of kneeling and putting regular, constant pressure on the front of your knee. 

So if you have a trade like laying flooring or carpet, you may experience housemaid's knee. You'll have difficulty bending and straightening your knee as the result of a swollen bursa. 

The swelling and pain usually occur gradually over time because of regular pressure on your knee unless you experience a blow to the front of your knee.

7. Patellar Tendonitis

After a long time of jumping or kicking movements, the tendon at the front of your knee may have micro-tears or become inflamed. The pain you experience as a result of this prolonged jumping and kicking is called patellar tendonitis. 

This overuse injury usually goes away with time, rest, and ice. If you take time to rest and treat your knee, you can avoid further, long-term damage. 

8. ITBS 

The thick band on the outside of your thigh and knee is your iliotibial band. When you feel pain on the outside of your knee, you could easily have ITBS or iliotibial band syndrome, also known as IT syndrome. 

When you have ITBS, you'll feel pain on the outside of your knee, and you will hear or feel a grinding or popping sensation when you bend your knee. 

ITBS comes on gradually as you run or exercise. If you've recently begun an exercise regimen or increased your milage quickly, you can develop this syndrome. 

Rest, stretching, and ice will alleviate your symptoms and prevent further injury. 

9. Sprain

Fou different ligaments control your knee. When you sprain your knee, you stretch or mildly tear one of those ligaments. The amount of damage your knee incurs determines the grade of the sprain. 

Sprains occur quickly due to an excessive force or a sudden twist of the knee. You will experience pain immediately, and you'll have a hard time bending or straightening your knee. 

10. Meniscus Tear

Meniscus tears are common causes of pain when bending your knee. The meniscus can tear as the result of wear and tear or a sudden knee twist. 

The meniscus will rarely tear cleanly. Rather, it will tear unevenly, sometimes even leaving a jagged edge or fray that will get caught in the joint. As a result, the joint will flare up, and you will not be able to move the joint easily. 

When you have a torn meniscus, you'll experience pain going up or downstairs or squatting down. You will have limited knee movement, and sometimes the knee may feel locked. The joint will most likely swell. 

You can alleviate some of the pain with rest and ice, but ultimately, you will need surgery to repair the torn meniscus. 

11. ACL Tear

The ACL is the anterior cruciating ligament, one of the major, stabilizing ligaments over your knee. It keeps your knee in line with your ankle and your hip. 

You can sustain an ACL tear when you experience trauma to your knee, be it through a sport or an accident. When the ligament tears, you will experience pain and the inability to control your knee joint. An ACL tear is so serious that some refer to it as a "blown knee." 

You will most likely need surgery to repair the tear if you have a complete tear. If you have a mild tear, you can sometimes experience relief through physical therapy. 

You may wonder, how soon can I bend my knee after ACL surgery. The answer depends wholly on the amount of physical therapy you do and how well you listen to your doctor. If you follow your doctor's advice, you will recover and regain full mobility. 

Some people might be able to walk with a torn ACL

12. Sitting Too Long

You do not need to have a traumatic injury to experience knee pain. Sometimes when you can't bed your knee without pain, you've been sitting for too long.

The design of your desk chair can cause knee pain. When your desk chair is not at the right height for your desk, you sit with your knee awkwardly bent for a long period.

This awkward position can lead to knee pain. So if you're experiencing knee pain after work, try adjusting your chair or desk height.

Make sure you have a chair that supports your spinal curves and is at a height where you rest your feet flat on the floor. Your thighs should be parallel to the floor. Keep the monitor directly in front of you at eye level, and keep your keyboard directly in front of your monitor.

13. Dead Butt Syndrome

There is a problem called dead butt syndrome. When you sit for long periods, your butt muscles will go numb and sometimes even be a little sore. Your muscles shorten, pulling up on the rest of your leg and causing knee pain. 

You can remedy dead butt syndrome in a few different ways. Take frequent walk breaks so you engage your glutes (butt muscles) regularly. Before you engage in strenuous exercise, try to wake those muscles up with some dynamic stretching. 

Treat Your Pain

Now that you know why you can't bend your knee without pain, seek treatment. 

Learn more about us by visiting our website. We have all kinds of solutions for knee pain, including braces and helpful articles. Take time to contact us for all your knee pain solutions. 


  • Henry

    I was playing football, cleared a ball nd landed wrongly on my right knee, 1 month nd still feeling the pain, as i walk, sit, bend, lay down, i do not take pain killers,bcoz i have ulcer, what should i do…

  • john Pollack

    i was in 2 rehabs in severe pain without the ability to straignext day hten my knee . then the pain lessened and i started walking with a walker. on my release at home i continued walking and i heard a crack. the pain lessoned and my knee could not sraighten past 140 degrees. still the same after 2 months. i pray a lot…in a wheelchair and sleep in a recliner….
  • Debra

    I had a torn meniscus that was stuck in my joint. I could not fully extend or bend my knee. The MRI showed a tear but not that it was stuck in my joint. I did PT and had severe swelling and pain. After 6 months I had surgery which is when the stuck meniscus was removed. It’s been one month I still cannot fully extend my knee but it’s close. I cannot fully bend my knee without a lot of pain. I do PT with stretching daily. I have a lot of lateral pain and numbness in my thigh with some burning. I’m very concerned there is more wrong. What can I do?

  • Kion

    I can’t bend my left knee all the way back without pain behind it, also feel pain on inside of knee

  • Rebecca

    Tried to sit this evening sharp pain shot in middle of knee.
    Tried to take bath could not bend my left knee to sit in tub. Had to call spouse to get out of bath.

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