What Causes a Stiff Knee After Sitting?

Several factors can contribute to knee stiffness, which is characterized by tightness in the joint, possibly with pain, difficulty moving the joint, and swelling. This problem usually occurs after a period of sitting or inactivity. Injuries and conditions that affect the knee joint, like osteoarthritis or rheumatoid arthritis (RA), can make knee stiffness worse.

This article explains the reasons your knee may feel stiff, how a doctor will determine the cause, and treatment options for different conditions.

Verywell / Julie Bang

Causes of Knee Stiffness

Most people experience stiff knees 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 your ability to freely move the joint. A number of conditions can lead to inflammation and knee stiffness.


Bursitis is usually a temporary condition that occurs when the bursae, sacs of fluid that protect the joint, become inflamed. There are several bursae in each knee joint.

Normally, bursae create a cushion within the knee so that bones and other tissues don't rub hard against each other. This reduces friction to prevent wear and tear.

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.


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 age 60 and over. However, if the knee joint is overused or injured frequently, osteoarthritis can affect young people as well.

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


Competitive athletics or everyday activities can put stress on the knee or force you to twist it wrong, resulting in an injury that comes with stiffness. Stiffness is more likely if the injury causes swelling and pain.

One common injury is a ligament injury. This problem can happen if you bend the joint past what would be its normal range of motion. Ligament injuries can also occur during an accident or other type of traumatic damage.

A meniscus tear is another common injury. The meniscus is a C-shaped piece of cartilage that sits between the bones in the knee joint. It acts like a shock absorber.

Tears to this cartilage can occur if the knee is twisted wrong. It's a common problem in sports that require a lot of squatting, twisting, and changing positions. When the meniscus tears, you may feel a pop in the knee.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) causes pain in the front of the knee and around the patella or kneecap. PFPS is often the result of overuse or poor alignment 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 more often than men.

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


Postoperative knee stiffness, or stiffness that occurs after surgery, is not unusual. Arthrofibrosis, also called stiff knee syndrome, is one type of post-op problem.

This condition is a result of the body's natural process of building up scar tissue in response to surgery or a trauma. With arthrofibrosis, too much scar tissue builds up around the knee joint, causing the knee to tighten.

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 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 healthcare provider 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


Your doctor will first take a history of your symptoms and ask about any recent injuries. To pinpoint the cause of stiffness, several types of tests might be done.

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

  • Blood tests to look for signs of arthritis
  • X-rays to diagnose a possible fracture or significant arthritic changes
  • Magnetic resonance imaging (MRI) to detect stress fractures or soft tissue injuries, such as ligament or tendon tears


Treatment depends on the cause of your knee stiffness. Conditions like osteoarthritis and RA will require long-term treatment and follow-up with your healthcare provider.

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 relieve knee stiffness.

These strategies include:

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

Medical Treatment

Depending on your condition, your doctor might recommend additional treatment along with self-care.

Treatment options include:

Even if you are sent for other medical treatments, you should continue to follow self-care strategies at home for the best results.


Stiff knees are often the result of overuse or injury, but disease can also limit your mobility. To prevent problems, stretch and exercise your legs regularly.

Even with careful care, you may find that your knees are still stiff. Other symptoms may develop, too, like swelling or fever. See your doctor for a physical exam and be prepared to undergo some blood and imaging tests in order to understand why your knees are stiff.

After a diagnosis, your doctor will develop a plan to either help you regain full movement without pain, or to help you manage discomfort and physical limitations that cannot be reversed. Medication, physical therapy, and surgery are commonly used to treat knee stiffness.

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 doctor can help you create a treatment plan that works for you and relieves your symptoms.

The earlier you figure out what's causing your knee stiffness, the better chance you'll have of recovering knee movement. So don't ignore pain or changes in your ability to sit, stand, or move because of knee pain.

Frequently Asked Questions

  • Why does my knee hurt while sitting?

    Many people with patellofemoral pain syndrome (PFPS) report that their knee hurts while sitting, especially during prolonged sitting. This condition is often identified by pain felt underneath and around the kneecap. Effective treatment for PFPS can come in the form of physical therapy and exercise that focuses on the quadriceps, hamstrings, and hip muscles.

  • How do I prevent stiff knees?

    There are a few ways to help prevent stiff knees. Before working out or engaging in physical activity, remember to properly stretch each part of your body. Low-impact exercises like yoga or hamstring curls can reduce stiffness and strengthen the muscles of the knee joint. If you work from home, stand up every 30 minutes to stretch your legs or install a standing desk to avoid sitting for too long.

  • Why is there tightness behind my knee?

    Anterior cruciate ligament (ACL) tear, posterior cruciate ligament (PCL) tear, and Baker's cyst are a few conditions that can cause tightness behind the knee. ACL tears are commonly seen as sports injuries, but ACL and PCL tears can happen due to any physical activity. The only way to diagnose your knee tightness is by visiting a healthcare provider.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  5. American Academy of Orthopaedic Surgeons. Knee Exercises.

By Kimberly Charleson
Kimberly is a health and wellness content writer crafting well-researched content that answers your health questions.