The 13 Potential Causes of Knee Pain When Attempting to Bend

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  • Post last modified:October 6, 2023

Mobility is everything. Our world comprehends this concept now more than ever. When you cannot travel to your desired destination at your preferred time, frustration sets in. When you cannot flex your knee without discomfort, you quickly find yourself restricted.

You may ponder, why can’t you flex your knee without discomfort? Knee discomfort arises from one of three issues. An abrupt injury, an overuse injury, or a disease can lead to knee discomfort when bending. 

Continue reading to acquire comprehensive knowledge about what to do when you cannot bend your knee without pain. 

The Functioning of a Knee

To grasp the potential problems with your knee and why it causes pain when you bend it, you need to comprehend the joint itself. Biologists label the knee joint as a pivot joint. This indicates that it has the ability to both bend and straighten. 

Here are the primary components of your knee and the ways they collaborate when you bend your knee: 

  • Muscles: You possess three major muscles that work in harmony for your knee to move. Your quadriceps (thigh muscle), hamstring (muscle behind your thigh), and calf (muscle on your lower leg) all operate together. When you flex your knee, for instance, your hamstrings contract and your quads relax. 
  • Bones: Your femur (thigh bone), tibia (shin bone), and patella (knee cap) function collectively to enable your knee to bend. The patella rests in a groove in your femur, and the upper and lower leg bones will roll, glide, and rotate around the patella. Your muscles govern the movement of those bones. 
  • Cartilage: Your knee contains cartilage in the knee cap, providing cushioning for the bones to ensure shock absorption. The meniscus is that cartilage. It is a spongy material that moves along with the motion of your upper and lower thigh bones. 
  • Ligaments and tendons: These are the fibrous tissues that connect your bones to bones (ligaments) and bones to muscles (tendons). They stabilize your knee, preventing it from becoming misaligned as you bend. They maintain the alignment of the knee joint with your hip and ankle. 

All of these components collaborate to create a seamless, pain-free joint as you bend and straighten your leg. When any one of these components malfunctions due to a disease or injury or simply due to regular wear-and-tear, you end up with a knee that cannot be straightened or bent without pain. 

Causes for Inability to Bend Your Knee Without Pain

Pain is debilitating. It has the ability to hinder basic mobility. If you are unable to bend your knee without pain, then you are encountering one of three issues. 

You may have an injury, ailment, or degeneration in your knee. Here are the primary causes for experiencing knee pain when bending. 

1. Arthritis

Arthritis is an inflamed joint. Countless individuals worldwide suffer from it. Knee pain when bending typically results from osteoarthritis. 

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

  1. Arthritis

    Arthritis arises due to a range of causes. If you’ve injured your knee in the past or if you have a family history of arthritis, you are susceptible to the disease. Additionally, if you are overweight and alter your gait due to the excess weight, you are prone to arthritis.

    When afflicted with arthritis in your knee, the pain may commence in the morning or arise when attempting to bend your knee after prolonged sitting. The pain may even lead to stiffness in your leg, exacerbating the difficulty of bending. Gentle movement can alleviate some discomfort, but activities that involve frequent bending, such as climbing stairs or constantly stooping down, will intensify the pain.

    Arthritis generally develops gradually over time. The symptoms come and go, worsening as time elapses. Typically, arthritis affects individuals aged 65 and above.

  2. Baker’s Cyst

    Baker’s Cyst can ensue from arthritis. This form of cyst develops when the bursa at the back of your knee swells.

    A Baker’s Cyst occurs when excess fluid from the knee joint accumulates in the bursa. This leads to swelling at the back of the knee, accompanied by stiffness and soreness.

    The surplus fluid can arise as a consequence of arthritis. If you tear your cartilage or have gout, excess fluid can accumulate.

    The knee will become rigid, and both bending and straightening it will become difficult. Physical activity exacerbates the condition, while rest improves it. You may observe a small bulge at the back of your knee, similar to a water balloon.

  3. Osgood Schlatters

    Osgood Schlatter’s syndrome occurs during adolescence. While arthritis typically arises after the age of 65, Osgood Schlatter’s results in knee pain for teenagers.

    When teenagers experience pain while bending their knee, they might be undergoing this phenomenon that arises when bones grow faster than soft tissue.

    When your bones grow at a faster rate than your tendons or ligaments, your knee will ache. The patellar tendon over your kneecap experiences more tension in particular, leading to damage to the underlying bones.

    Rest and time alleviate the pain caused by Osgood Schlatters. Any form of knee injury recovery requires time and rest, but if you are young and care for your knee properly, it will serve you well throughout your lifetime.

  4. Runner’s Knee

    Runner’s knee can affect anyone, not just runners. Doctors refer to runner’s knee as anterior knee pain or patellofemoral pain syndrome.

    If your kneecap moves and exerts additional stress or friction on the underlying tissue when you bend or straighten your knee, you may have runner’s knee. Weak muscles can contribute to the development of runner’s knee. Furthermore, if you have abnormal biomechanics stemming from issues with your foot arches or irregular hip angles, you are susceptible to runner’s knee.

    You will be aware of having runner’s knee when you experience pain while bending your knee, with the pain typically concentrated at the front of the knee.

Your discomfort can also happen whenever you need to flex or crouch or when you initially move your knee after sitting for a while. You may also observe a grinding or scraping sound whenever you attempt to flex or straighten your knee.

Runner’s knee develops gradually.

5. Bursitis

When you have bursitis, you have an inflamed bursa. The bursa act as shock absorbers in your knee. The fluid-filled sacs absorb shock as you utilize 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 housemaid’s knee. With housemaid’s knee, the bursa just below your kneecap swells and causes pain. This occurs as a result of kneeling and applying 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 due to a swollen bursa.

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

7. Patellar Tendonitis

After an extended period 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.


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 flex your knee.

ITBS develops gradually as you run or exercise. If you’ve recently started an exercise regimen or increased your mileage quickly, you can develop this syndrome.

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

9. Sprain

Four different ligaments control your knee. When you sprain your knee, you stretch or slightly tear one of those ligaments. The extent of damage your knee sustains determines the grade of the sprain.

Sprains occur rapidly due to excessive force or a sudden twist of the knee. You will experience pain immediately, and you’ll have difficulty bending or straightening your knee.

10. Meniscus Tear

Meniscus tears are common causes of pain when flexing your knee.

The meniscus has the potential to rupture due to erosion and attrition or an abrupt twist of the knee.

The meniscus will seldom tear cleanly. Instead, it will tear unevenly, occasionally even leaving a jagged edge or fray that will become entangled in the joint. As a result, the joint will become inflamed, and you will have difficulties moving it easily.

When you have a torn meniscus, you will experience pain while ascending or descending stairs or when crouching down. Your knee movement will be limited, and at times, the knee may feel locked. The joint will most likely become swollen.

You can alleviate some of the pain by resting and applying ice, but ultimately, surgery will be necessary to repair the torn meniscus.

11. ACL Tear

The ACL is the anterior cruciating ligament, one of the main, stabilizing ligaments above your knee. It keeps your knee aligned with your ankle and hip.

You can incur an ACL tear when you undergo trauma to your knee, whether it be through sports or an accident. When the ligament tears, you will experience pain and an inability to control your knee joint. An ACL tear is so severe that some refer to it as a “blown knee.”

If you have a complete tear, you will likely require surgery to repair the tear. In the case of a mild tear, you may sometimes find relief through physical therapy.

You may wonder, how soon can I flex my knee after ACL surgery. The answer entirely depends on the amount of physical therapy you undergo and how well you heed your doctor’s advice. If you follow your doctor’s guidance, you will recover and regain full mobility.

Some individuals may have the ability to walk with a tore ACL.

12. Sitting Too Long

You do not need to sustain a traumatic injury to experience knee pain. Occasionally, when you are unable to bend your knee without pain, it may be a result of sitting for an extended period.

The design of your desk chair can contribute to knee pain. When your desk chair is not at the appropriate height for your desk, you sit with your knee in an awkwardly bent position for a prolonged time.

This awkward posture can lead to knee pain. Therefore, if you experience knee pain after work, attempt adjusting your chair or desk height.

Ensure that you have a chair that supports the natural curvature of your spine and is at a height where you can 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 position your keyboard directly in front of your monitor.

13. Dead Butt Syndrome

There is a condition known as dead butt syndrome. When you sit for prolonged periods, your gluteus muscles may become numb and sometimes even a bit sore. Your muscles contract, pulling up on the rest of your leg and resulting in knee pain.

You can address dead butt syndrome in a few different ways. Take frequent breaks to go for walks so that you engage your gluteus muscles regularly. Prior to engaging in strenuous exercise, try to activate those muscles with some dynamic stretching.

Treat Your Pain

Now that you understand why you are unable to bend your knee without pain, seek treatment.

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We possess a wide array of remedies for suffering in the knee area, such as supports and informative write-ups. Make sure to allocate a moment to reach out to us regarding every one of your knee pain resolutions.