Knee Stiffness: Causes and How to Loosen a Stiff Knee

What knee stiffness means

The knee normally straightens fully (0 degrees) and bends to about 135 degrees or more. Stiffness can mean:

• A feeling of tightness that eases as you move, typical of arthritis
• True loss of range, where the knee physically cannot fully bend or straighten, from swelling, scar tissue, or a mechanical block such as a torn piece of meniscus

It often comes with knee pain and swelling, but some people have stiffness without much pain, especially with early arthritis or a Baker's cyst.

Common causes of knee stiffness

Osteoarthritis

Knee osteoarthritis is wear and repair of the joint cartilage and bone. It causes:

• stiffness after rest or first thing in the morning, usually lasting less than 30 minutes
• pain with walking, stairs and getting up from a chair
• grinding or creaking (crepitus)
• gradual loss of full bending or straightening
• occasional swelling

It is most common after 50, after previous knee injuries, and in people with excess weight.

Swelling after injury

Any injury that causes fluid or blood in the joint makes the knee feel tight and stiff. Rapid swelling within hours suggests bleeding, often from an ACL tear or a fracture. Slower swelling over a day suggests a meniscus tear.

Meniscus tear

A torn meniscus can cause stiffness, swelling, catching and, if a torn piece gets stuck, locking that stops you straightening the knee.

Baker's cyst

A Baker's cyst is a fluid-filled swelling behind the knee, usually caused by arthritis or a meniscus tear. It causes tightness behind the knee, especially when fully bending or straightening. If it bursts, fluid tracks into the calf, causing pain and swelling that can mimic a blood clot.

Inflammatory arthritis

• Rheumatoid arthritis: morning stiffness lasting more than an hour, usually in several joints on both sides, often the hands and feet as well as the knees.
• Psoriatic arthritis and reactive arthritis: stiffness and swelling, sometimes in one knee, with skin, eye, bowel or urinary symptoms.

Gout and pseudogout

Crystals in the joint cause sudden, intensely painful, hot, swollen and stiff knees. Gout more often affects the big toe but can involve the knee. Pseudogout (calcium pyrophosphate crystals) commonly affects the knee in older adults.

Stiffness after knee surgery

After a knee replacement or ACL reconstruction, scar tissue can limit movement (arthrofibrosis). Early, consistent physical therapy is the main prevention. Manipulation under anesthesia or surgery to release scar tissue may be needed if movement does not improve.

Other causes

• Patellofemoral pain: stiffness and aching around the kneecap after sitting with bent knees ("moviegoer's knee").
• Tight muscles: tight quadriceps or hamstrings, especially after exercise.
• Septic arthritis: infection inside the joint, a medical emergency.

Morning stiffness vs stiffness after sitting

How doctors find the cause

A clinician will ask how the stiffness started, how long it lasts, whether there was an injury, and about swelling, locking, giving way and other joints. They will check range of movement, swelling, tenderness, stability and the back of the knee.

Tests may include:

• X-rays to show arthritis, fractures and joint space narrowing
• MRI for meniscus and ligament injuries
• Ultrasound for Baker's cysts and fluid
• Joint aspiration: removing fluid with a needle to look for crystals or infection
• Blood tests for inflammation, rheumatoid factor and anti-CCP antibodies, and uric acid

How to loosen a stiff knee

Home care

• Keep moving: gentle movement is the best treatment for arthritis stiffness. Avoid long periods of sitting, and get up and walk every 30 to 60 minutes.
• Range-of-motion exercises: heel slides lying on your back, seated knee bends and straightening, and gentle stationary cycling.
• Strengthen: stronger quadriceps and hip muscles reduce arthritis pain and stiffness. Try straight leg raises, mini squats and step-ups.
• Warm up: a warm shower or heat pack for 15 to 20 minutes before activity loosens a stiff knee. Use ice after activity if the knee is swollen.
• Low-impact exercise: walking, swimming, water aerobics and cycling.
• Weight management: each pound of body weight puts several pounds of force through the knee when walking.
• Pain relief: acetaminophen (paracetamol), or an NSAID such as ibuprofen or a topical NSAID gel, at the label dose. Topical gels are a good first choice for older adults. Avoid oral NSAIDs with kidney disease, stomach ulcers or some heart conditions.

Medical treatment

• Physical therapy
• Steroid injections into the joint for flare-ups of arthritis
• Medicines that control inflammatory arthritis (disease-modifying antirheumatic drugs)
• Gout treatment, including long-term urate-lowering therapy
• Antibiotics and joint washout for infection
• Arthroscopic surgery for a locked knee from a meniscus tear
• Knee replacement for severe osteoarthritis that limits daily life despite other treatments

Frequently asked questions

Why is my knee stiff after sitting?

Stiffness after sitting is common with knee osteoarthritis and kneecap (patellofemoral) problems. Joint fluid and tissues stiffen with inactivity, then loosen once you move. It usually eases within a few minutes of walking. Getting up regularly and strengthening exercises help.

What causes knee stiffness without pain?

Painless stiffness can come from early osteoarthritis, a Baker's cyst behind the knee, tight thigh muscles, or mild swelling after activity. It can also follow knee surgery as scar tissue forms. If it limits movement or lasts more than a few weeks, have it assessed.

Is morning knee stiffness a sign of arthritis?

Often, yes. Brief morning stiffness lasting under 30 minutes is typical of osteoarthritis. Morning stiffness lasting more than an hour, especially with stiffness in other joints, suggests inflammatory arthritis such as rheumatoid arthritis and should be checked by a doctor.

How do you loosen a stiff knee?

Gentle movement is the best way. Try heel slides, seated knee bends and stationary cycling, apply heat before activity, and strengthen your thigh and hip muscles. Avoid sitting for long periods. If stiffness follows an injury or surgery, follow your physical therapist's program.

Why does my knee feel stiff and tight behind it?

Tightness behind the knee is often caused by a Baker's cyst, a fluid swelling linked to arthritis or a meniscus tear. Tight hamstrings or calf muscles are another cause. If the calf becomes swollen and painful, see a doctor urgently to rule out a blood clot.