What Causes a Stiff Knee After Sitting?

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Several factors can contribute to knee stiffness, which is usually most noticeable after a brief period of sitting or inactivity. Injuries and conditions that affect the knee joint, like osteoarthritis or rheumatoid arthritis (RA), can cause your knees to feel stiff. Knee stiffness is characterized by a feeling of tightness in and around the knee joint, which can be accompanied by pain, difficulty moving the joint, and/or swelling.

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Causes of Knee Stiffness

Most people experience knee stiffness after sitting for a long period of time. It's usually the result of inflammation and fluid build-up in the knee joint, which causes swelling and decreases the ability to freely move the joint. A number of conditions can lead to inflammation, and subsequently, knee stiffness.

Bursitis

Bursitis is usually a temporary condition that occurs when the bursae become inflamed. Bursae are fluid-filled sacs that help reduce friction in the joints as they move. There are several bursae in each knee joint.

Overuse is the most common cause of bursitis. If you develop this condition, your knees can feel stiff after you sit for long periods of time.

Arthritis

Osteoarthritis, also known as wear-and-tear arthritis, can 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.

RA, an autoimmune disease, is commonly associated with joint stiffness. Morning stiffness is a hallmark feature of RA. If you experience knee stiffness along with additional symptoms, like fever and fatigue, you may have RA.

Injury

Knee joint injuries can occur during athletic or everyday activities. Along with stiffness, you are likely to experience swelling and pain from the injury.

For example, a ligament injury can occur due to hyperextension of the knee or traumatic damage. Another common injury is a tear of the meniscus, a c-shape portion of cartilage that sits along the border of the knee joint, providing shock absorption. This can occur due to twisting the knee, and it is common in sports that require a lot of squatting, twisting, and changing positions. You would feel a pop if you tear your meniscus.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) causes pain in the front of the knee and around the patella (kneecap). 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 than men.

PMPS causes stiffness and pain in and under the kneecap, especially after sitting for long periods of time.

Surgery

Surgery can cause a degree of postoperative knee stiffness. Arthrofibrosis, also called stiff knee syndrome, can happen after knee surgery. The body's natural response to trauma, such as from injury or surgery, is to make scar tissues. Arthrofibrosis develops when there is too much scar tissue around the knee joint, causing the knee to tighten and stiffen.

Arthrofibrosis can occur after common knee surgeries, including:

Low Flexibility or Strength

Maintaining flexibility throughout the body can help prevent some types of knee stiffness.

To avoid stiffness from tight muscles, add stretching to your fitness routine and prioritize strength-building exercises.

  • Gentle stretching: Can improve the ability of your joints to move through their normal range of motion with minimal restriction and tightness.
  • Strengthening: Strong muscles around your knee joints can also make them less prone to injury.

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:

  • Swelling
  • Decreased sensation
  • Diminished inability to move the knee joint
  • Diminished or absent pulses in the feet
  • Cold or bluish feet or toes
  • High fever
  • Bleeding or bruising
  • Uncontrollable pain

Diagnosis

When you are seen and evaluated for knee stiffness, your doctor will take a history of your symptoms and ask about any recent injuries.

Tests to diagnose the underlying cause of stiff knees can include:

  • Blood tests to look for signs of arthritis
  • X-rays to investigate a possible fracture or significant arthritic changes
  • MRI, which can detect stress fractures or soft tissue injuries, such as ligament or tendon tears

Treatment

Treatment will depend on the cause of your knee stiffness. Conditions like osteoarthritis and RA 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, there are several 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:

Above all, listen to your body. Don't overdo it.

Medical Treatment

Depending on your condition, your doctor might also recommend a treatment plan along with self-care recommendations.

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 may interfere with your daily life. Whether it comes from an injury or an underlying condition, your doctors 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 outcome will be. As a preventative method, it's a good idea to regularly 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.