What Causes a Stiff Knee After Sitting?

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You may experience knee stiffness with pain, especially after sitting or being inactive. Injury and conditions that affect the knee joint like osteoarthritis and rheumatoid arthritis can also be reasons why your knees feel stiff. Knee stiffness is characterized by difficulty moving the knee and a feeling of tightness in and around the joint. Other symptoms like muscle weakness and swelling may also occur alongside a stiff knee.

stiff knees

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Causes of Knee Stiffness

Most people experience knee stiffness after sitting for a long period of time. Stiff knees are a result of inflammation and fluid build-up in the knee joint, which causes tightness and inability to move it freely. A number of conditions can lead to inflammation and subsequently knee stiffness.


Bursitis occurs when the bursa becomes inflamed. Bursae are fluid-filled sacs that help reduce friction in the joints as they move, and there are several bursae in the knee joints. Overuse is the most common cause of bursitis. Sitting for long periods of time can often cause the knee to feel stiff for people with this condition.


Osteoarthritis, also known as wear-and-tear arthritis, can also cause stiff knees. It is the most common form of arthritis, affecting 10% of men and 13 % of women in the 60-and-over demographic. However, if the knee joint is overused or injured frequently, osteoarthritis can affect young people as well.

Rheumatoid arthritis (RA), an autoimmune disease, is also commonly associated with joint stiffness. If you experience knee stiffness along with additional symptoms like fever and fatigue, your may have RA. A hallmark feature of RA is morning stiffness.


Injury to the knee joint can happen to athletes playing sports or to anyone during everyday activities. Ligament injuries can happen from hyperextension of the knee or trauma. Along with stiffness, you may experience swelling and pain from the injury.

Another common injury is a tear of the meniscus, which is the cartilage of the knee. This often happens when twisting the knee, and is common in sports that require a lot of squatting, twisting, and changing positions. You will feel a pop when your meniscus is torn. Similarly, this injury will cause knee pain, swelling, and stiffness.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) describes pain in the front of the knee and around the kneecap (patella). PFPS is often the result of overuse or malalignment of the kneecap. It's also referred to as runner's knee or jumper's knee because it's most common in people who play sports. It affects women at a higher rate.

PMPS causes stiffness as well as pain in and under the kneecap. Sitting for long periods of time will result in increased pain and stiffness.


Surgery often results in some level of knee stiffness post-op. Arthrofibrosis, also called stiff knee syndrome, can happen after surgery on the knee. The body's natural response to trauma, such as from injury or surgery, is to make scar tissues. Arthrofibrosis is when there is too much scar tissue around the knee joint, causing the knee to tighten and resulting in knee stiffness.

Arthrofibrosis can occur after common knee surgeries, including:

Low Flexibility or Strength

Maintaining flexibility (the ability of joints to move through an unrestricted range of motion) throughout the body is beneficial in the long run for minimizing knee stiffness. Having the support of strong muscles around the knee joint also makes it less prone to injury. To avoid stiffness from tight muscles, add stretching to your fitness routine and prioritize strength-building exercises for the legs to support the knees.

When to See a Doctor

While knee stiffness is common, it can also be the sign of a serious condition. Call your doctor immediately if you experience the following symptoms:

  • Increased swelling
  • Paralysis
  • Loss of sensation
  • Complete inability to move the knee joint
  • Absent pulses in the feet
  • Coldness of the feet
  • High fever
  • Severe bleeding
  • Uncontrollable pain


Your doctor will take a full history, take note of all symptoms, and ask about any recent injuries. Tests to diagnose the underlying cause of stiff knees include blood tests to look for signs of arthritis, x-ray to investigate a possible fracture, or a CT scan to look for tears.


Treatment will depend on the cause of your knee stiffness. Conditions like osteoarthritis and rheumatoid arthritis will require long-term treatment and follow-up with your doctor. Whether your knee stiffness is the result of a chronic disease or an injury, however, there are ways you can get relief for your stiff knees.

Self-Care Strategies

Self-care can be done at home to prevent or alleviate knee stiffness. These strategies include:

  • RICE (rest, ice, compression, and elevation)
  • Warming up before stretching
  • Stretching before working out
  • Taking non-steroidal anti-inflammatory drugs like aspirin or ibuprofen
  • Wearing a knee brace
  • Strengthening the surrounding muscles
  • Incorporating walks and a standing desk into your work routine
  • Choose low-impact exercise like yoga

Above all, listen to your body. Don't overdo it, and if the stiffness came from an injury, seek medical help.

Medical Treatment

If your knee pain is serious and requires medical attention, your doctor will move forward with a treatment plan depending on your diagnosis.

Treatment options include:

Keep in mind that self-care strategies can be done alongside medical treatment for best results.

A Word From Verywell

Stiffness in the knee joint can be alarming and interfere with daily life. Whether this symptom comes from an injury or underlying condition, doctors see it often and can help you create a treatment plan that works for you and alleviates your symptoms. The earlier you identify what is causing your knee stiffness, the better your outlook will be. Practice self-care and choose exercises that keep your knees healthy and range of motion intact.

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  1. Zhang Y, Jordan JM. Epidemiology of osteoarthritis. Clin Geriatr Med. 2010;26(3):355-369. doi:10.1016/j.cger.2010.03.001

  2. American Academy of Orthopedic Surgeons. Patellofemoral Pain Syndrome. Updated October 2020.

  3. Healthgrades. Stiff Knee. Updated November 30, 2020.