Knee Stiffness or Tightness: What It Means and What Helps

What does a stiff knee mean?

A stiff knee has lost some of its normal range of motion. A healthy knee bends to about 135 degrees and straightens fully to 0 degrees. Stiffness can come from three places:

• Inside the joint: fluid (an effusion), worn cartilage, bone spurs, a torn meniscus or loose bodies that block movement.
• The joint lining and capsule: inflammation in arthritis, or scar tissue after surgery or injury.
• Around the joint: tight quadriceps, hamstrings, calf muscles or iliotibial band, or a cyst behind the knee.

"Tightness" usually describes a feeling of tension, often with swelling, while "stiffness" describes reduced movement. Many people have both.

Causes of knee stiffness

Osteoarthritis

Osteoarthritis of the knee is the most common cause in adults over 50. Cartilage thins and bone spurs form. Stiffness is worst after rest, the "gel" feeling when you first stand up after sitting, and usually eases within 30 minutes of moving. The knee may creak, ache after activity and gradually lose full straightening.

Swelling after injury

Any fluid in the joint makes it tight and stiff, because the knee cannot bend fully when the capsule is distended. Swelling within hours of a twist suggests bleeding into the joint from an ACL injury or a fracture. Swelling that builds over a day or two is more typical of a meniscal tear, which may also catch or lock.

Inflammatory arthritis

Rheumatoid arthritis, psoriatic arthritis and reactive arthritis cause a warm, swollen knee with morning stiffness lasting an hour or more, often in several joints. Gout and pseudogout cause sudden, very painful, red, swollen knees.

Baker's cyst

A Baker's cyst is a fluid-filled swelling behind the knee, usually from arthritis or a meniscus tear. It causes tightness behind the knee, worse when fully bending or straightening. If it ruptures, fluid tracks into the calf and causes pain and swelling that mimics a blood clot.

Tight muscles

Tight hamstrings cause tightness behind the knee, tight quadriceps limit bending, and a tight iliotibial band causes outer knee tension in runners and cyclists. This tightness is usually felt in the muscle or tendon rather than deep in the joint, and improves with stretching.

After surgery or immobilization

Stiffness is expected after knee replacement, ACL reconstruction and time in a brace. Some people develop arthrofibrosis, excess scar tissue that limits motion despite therapy.

Infection

Septic arthritis causes a hot, swollen, very painful knee that you cannot move, usually with fever. It is an emergency because it can destroy cartilage within days.

Stiff knee patterns and what they suggest

How doctors assess a stiff knee

A doctor will ask when the stiffness started, how long it lasts in the morning, about injuries, swelling, locking and other painful joints. They will measure how far the knee bends and straightens, look for fluid, test ligaments and the meniscus, and compare with the other knee.

Tests may include X-rays (standing views show arthritis), an ultrasound for a Baker's cyst, an MRI for meniscus or ligament injury, blood tests for inflammation, and drawing fluid from the knee with a needle (aspiration) to test for infection or crystals.

How to loosen a stiff knee

Daily movement and exercise

• Heel slides: lying on your back, slide your heel toward your buttock, then straighten. 10 to 15 times, twice a day.
• Quad sets: sitting with the leg straight, tighten your thigh to push the back of the knee down. Hold 5 seconds, 10 times.
• Hamstring stretch: sitting with the leg straight on a bed or step, lean forward gently until you feel a stretch behind the thigh. Hold 30 seconds, 3 times.
• Calf stretch: against a wall, with the back leg straight. Hold 30 seconds.
• Stationary cycling on low resistance is one of the best ways to improve knee bending.

Strengthening the quadriceps and hip muscles reduces arthritis pain and stiffness over 6 to 12 weeks.

Other self-care

• Warm the knee with a warm shower or heat pack before exercise to ease stiffness. Use ice after activity if it swells.
• Avoid sitting still for long periods; get up and walk every 30 to 60 minutes.
• Losing even 5 to 10% of body weight noticeably reduces knee load and symptoms in osteoarthritis.
• Over-the-counter pain relievers or topical NSAID gels can help, following the label. Ask a doctor first if you have kidney, stomach or heart problems.

Medical treatment

Physical therapy, steroid injections for inflammatory flares or arthritis, draining a large effusion, disease-modifying medicines for rheumatoid arthritis, arthroscopic surgery for a locked knee from a displaced meniscus tear, and knee replacement for severe arthritis.

Frequently asked questions

What does it mean when your knee feels stiff?

It means the knee is not bending or straightening as easily as normal. The most common reasons are osteoarthritis, fluid in the joint after an injury, tight muscles, or inflammatory arthritis. How long the stiffness lasts and whether the knee is swollen help point to the cause.

Why does my knee feel tight behind it?

Tightness behind the knee often comes from tight hamstring or calf muscles, or a Baker's cyst, a fluid swelling linked to arthritis or a meniscus tear. If the calf becomes swollen, warm and painful, see a doctor promptly to rule out a blood clot.

Why is my knee stiff after sitting?

Short-lived stiffness after sitting, which loosens within a few minutes of walking, is typical of knee osteoarthritis. Joint fluid thickens and muscles tighten when you are still. Getting up every 30 to 60 minutes and doing gentle knee bends helps.

Should I walk on a stiff knee?

Usually yes. Gentle walking keeps the joint moving and the muscles strong, which reduces stiffness. Stop and get checked if the knee is hot and very swollen, locks, gives way, or you cannot bear weight.

When should I see a doctor for knee stiffness?

See a doctor if stiffness lasts more than a few weeks, follows an injury with swelling, comes with locking or giving way, or lasts over an hour each morning. Seek urgent care for a hot, red, swollen knee with fever.