Arthritis is often the underlying cause of knee pain in absence of an injury. This article describes 6 types of arthritis that can affect the knee.

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1. Osteoarthritis

Illustration of the anatomy of knee osteoarthritis

Osteoarthritis is characterized by cartilage degeneration and bony protrusions called osteophytes (bone spurs). In the knee, the most common sites of osteoarthritis include the tibia (shin bone), femur (thigh bone), and patella (kneecap).

The most common type of arthritis affecting the knee is osteoarthritis. Osteoarthritis occurs when a joint’s articular cartilage breaks down. In the knee, articular cartilage covers the top of the tibia (shin bone), bottom of the femur (thigh bone), and back of the patella (knee cap).

See What Is Knee Osteoarthritis?

Not everyone with knee osteoarthritis will get knee pain. Pain may occur if the loss of healthy cartilage:

  • Causes the bones of the joint to rub against one another.
  • Compromises the joint’s biomechanics in some other way.

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In the early stages of knee osteoarthritis, pain may be felt when doing specific activities, such as jogging. As osteoarthritis progresses, pain may be felt during daily activities.

See Knee Osteoarthritis Symptoms

Post-traumatic knee arthritis
Post-traumatic arthritis is a type of osteoarthritis. It develops after a meniscus tear, ligament injury, or other trauma. The injury may heal but wear-and-tear on the articular cartilage can accelerate. Post-traumatic arthritis may not become symptomatic until years after the injury.

Watch Knee Meniscus Tear Video


2. Rheumatoid Arthritis

Illustration of symmetrical joint pain from rheumatoid arthritis

Rheumatoid arthritis is an autoimmune disease that targets the synovial membrane surrounding many joints of the body. Some of the most common areas affected include the wrists, knees, and ankles.

Knee pain can be caused by an autoimmune disease called rheumatoid arthritis (RA). RA causes joint inflammation that can make the knee feel swollen, stiff, warm, and painful. Over time, untreated RA can cause permanent knee joint damage.

See What Is Rheumatoid Arthritis (RA)?

Rheumatoid arthritis often affects joints symmetrically, so if one knee is affected the other is also likely to be affected. Symptoms are also common in the hands and wrists. Episodes of RA may come and go and can be accompanied by other symptoms, such as fatigue.

See Rheumatoid Arthritis (RA) Symptoms

3. Psoriatic Arthritis

Illustration of a rash on the knee from psoriatic arthritis

Psoriatic arthritis is an autoimmune disease associated with psoriasis, a skin condition. Psoriasis often appears as an itchy red spot on the elbows, knees, or scalp; and psoriatic arthritis can manifest in the joints of the extremities, hips, knees, and spine.

Like rheumatoid arthritis, psoriatic arthritis is an autoimmune disease. When the knee is affected by psoriatic arthritis, the knee may feel painful, stiff, swollen, and tender. Other joints are often affected, particularly joints in the fingers and toes. Other common symptoms include fatigue and eye pain.

See What Is Psoriatic Arthritis?

Psoriasis is a skin condition. While estimates vary, recent research suggests about 20% of people with psoriasis also have psoriatic arthritis. 1 Alinaghi F, Calov M, Kristensen LE, et al. Prevalence of psoriatic arthritis in patients with psoriasis: A systematic review and meta-analysis of observational and clinical studies. J Am Acad Dermatol. 2018; Many people have psoriasis for years before experiencing joint pain associated with psoriatic arthritis.

See Psoriatic Arthritis Causes

4. Gout

Gout is an inflammatory arthritis that can cause a build-up of uric acid crystals (monosodium urate crystals) in the knee joint. These needle-like, microscopic crystals collect in the soft tissue of the knee joint, causing pain that can be excruciating, as well as swelling, redness, and warmth.

See All About Gout - Symptoms, Diagnosis, Treatment

About half of all gout cases affect the big toe joint (metatarsophalangeal joint), but other cases affect the knee or another joint.

5. Pseudogout: Calcium Pyrophosphate Deposition (CPPD)

Illustration of knee swelling from pseudogout caused by calcium pyrophospate

Pseudogout is a type of inflammatory arthritis that results from the buildup of calcium pyrophosphate crystals in the joints of the body. While less common than gout, pseudogout is more likely to affect the knee.

Like gout, pseudogout is caused by a build-up of microscopic crystals in a joint and can lead to sudden, severe knee pain, swelling, warmth, and redness. Pseudogout is less common than gout but more likely to affect the knee joint.

See All About Pseudogout - Symptoms, Diagnosis, Treatment

The microscopic crystals that cause pseudogout are called calcium pyrophosphate crystals. Doctors often refer to pseudogout as calcium pyrophosphate deposition (CPPD).


6. Reactive Arthritis

Illustration of inflamed synovial tissue in the knee cause by psoriatic arthritis

Reactive arthritis can result in inflammatory joint pain, most commonly in the knee, fingers, or low back. Other possible symptoms include problems involving the urinary tract, eyes, and skin.

Reactive arthritis commonly affects the knee, though it can affect any joint. Arthritis inflammation can make a knee achy, swollen, and/or red.

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Reactive arthritis develops as a reaction to an infection, such as a stomach bug or a sexually transmitted disease (STD). Days, weeks, or even months after the infection has resolved, a person may develop pain in one or more joints, inflamed eyes, and/or other symptoms.

See Infections that Can Cause Reactive Arthritis

The above conditions are common causes of arthritic knee pain. There are more than 100 types of arthritis that may include knee symptoms. People with chronic knee pain are advised to consult with their doctors for accurate diagnoses.

See Types of Arthritis

Dr. Matthew Levine is an orthopedic surgeon at Resurgens Orthopaedics. He specializes in joint replacement surgery and in treating hip and knee arthritis.