Osteoarthritis (OA) is a common form of arthritis that often affects the knee. In the early stages, a person may not notice any symptoms. In the later stages, however, they may experience mobility issues and may need a surgery.

OA of the knee affects the bones, cartilage, and synovium in the knee joint.

Cartilage is a slippery tissue that provides a smooth surface for joint motion and acts as a cushion between the bones. Synovium, which is soft and lines the joints, produces synovial fluid for lubrication and supplies nutrients and oxygen to the cartilage.

As these functions break down, they no longer protect the bones of the knee joint. This in turn can lead to bone damage.

OA of the knee can cause pain and stiffness. The symptoms worsen over time.

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OA of the knee takes several years to develop. Doctors often use stages to describe the progression.

They commonly use the Kellgren-Lawrence (KL) classification of OA to describe OA of the knee, but there are other grading systems. The original KL classification was published in 1957.

The stages below follow the KL classification, based on a series of X-ray images of OA of the knee.

Stage 1: Minor

An X-ray may not reveal any damage, but bony growths of bone called osteophytes can be an early sign of OA.

Other changes in the joint at this stage can include slight damage to the cartilage, and narrowing of the space between the bones in the joint.

At this stage, a person is unlikely to experience discomfort or pain. The joint will appear healthy on an X-ray. Gait changes are also unlikely.

Learn more about the early stages of OA of the knee here.

Stage 2: Mild

At this stage, an X-ray will possibly show narrowing of the space in the joint, and bone spurs.

A person may start to notice stiffness and joint pain, especially after resting for a while.

The area where the bones and tissues meet will start to harden. When the tissues harden, the bone becomes thicker and denser. A thin layer of bone will also develop beneath the cartilage in the joints.

There may be some minor damage, but the bones are not rubbing or scraping against each other. Synovial fluid is present, and it helps reduce friction, supporting the movement of the knee.

Stage 3: Moderate

At this stage, an X-ray will show:

  • a clear narrowing of the joint space
  • some development of bone spurs
  • some damage to cartilage and other tissue
  • a possible deformity at the ends of the bones

A person may notice:

  • pain and discomfort during daily activities, such as running, walking, kneeling, and bending
  • early signs of joint inflammation
  • swelling and fluid buildup around the joint due to synovitis, which people sometimes call water on the knee

As OA progresses, the cartilage will continue to thin and break down. The bones will respond by thickening and forming bony outward growths.

Stage 4: Severe

At this stage, an X-ray will show:

  • a severe narrowing of the joint space, as a result of which the bones meet and rub together
  • a significant development of bone spurs
  • clear damage to the cartilage, which may have become fully or almost fully eroded
  • a definite deformity at the ends of the bones

People may experience:

At this stage, a doctor may recommend surgery.

An individual may not notice symptoms in the early stages of OA.

If a person has knee pain, a doctor will ask about symptoms, including:

  • when and where pain and stiffness occur
  • whether the knee cracks or pops with movement
  • how long any pain lasts in the morning
  • how this affects their daily life
  • whether they are taking any medications
  • whether there is pain and fullness behind the knee, which may mean that a Baker’s cyst is present
  • whether the knee appears unstable
  • whether the joint has changed shape
  • whether the symptoms affect one or both knees

Pain from OA of the knee usually improves around 30 minutes after getting up from resting, but the pain from rheumatoid arthritis (RA) may last 45 minutes or longer.

The doctor will also:

The doctor will examine the joints, test their overall range of motion, and check for damage. They will pay close attention to any areas that are tender, painful, or swollen.

Possible tests include:

  • X-rays to assess damage to the joint
  • MRI scans to help detect early signs that an X-ray may not reveal
  • blood tests to help rule out other diseases, such as gout and RA

In some cases, a doctor may recommend a joint fluid test, which involves removing some fluid with a needle and sending it to a laboratory for testing. The results may show biomarkers of inflammation.

However, experts do not recommend this unless there are signs of swelling that could indicate joint inflammation or synovitis. In this case, tests could help detect RA.

Learn about types of knee arthritis here.

Treatment options depend on the stage of OA and how quickly the condition is progressing.

Stage 1

Any symptoms are usually minor, and acetaminophens or other over-the-counter (OTC) medications can often relieve the pain. A doctor may recommend specific exercises to help build strength and mobility.

According to the American Academy of Orthopaedic Surgeons (AAOS), there is not enough evidence to show that supplements such as glucosamine help.

Stage 2

Treatments can include:

  • taking pain relievers
  • attending physical therapy sessions to build or maintain strength and flexibility
  • wearing a knee brace designed to relieve pressure on the joints’ surfaces
  • wearing shoe inserts to reduce stress on the knee

At this stage, it may be necessary to adapt or change daily activities to avoid pain.

Stage 3

Treatments can include:

In the past, people used hyaluronic acid to treat pain. However, both the American College of Rheumatology (ACR) and the Arthritis Foundation (AF) advise against this, as there is not enough evidence to show that it is safe or effective.

Stage 4

At this stage, the cartilage has either significantly diminished or completely worn away.

A person can continue to use pain relief medication. A cane, walker, or brace can help them stay mobile.

A doctor may recommend surgery to replace or realign the joint.

Alternative remedies

The ACR and AF recommend that a person:

  • reach a moderate weight, if applicable
  • obtain information on how to manage their situation
  • practice tai chi
  • use a knee brace
  • do balance exercises
  • practice yoga
  • undergo cognitive behavioral therapy to help with pain, mood, and sleep problems

People may also try the following:

  • acupuncture
  • magnetic pulse therapy
  • needle lavage, which involves inserting a needle into the joint and injecting a saline solution

However, the AAOS notes there is not enough evidence to confirm these treatments are safe or effective.

Current guidelines suggest that people avoid using lateral or medial wedged insoles, glucosamine supplements, or chondroitin supplements, as research has not confirmed that they work.

Stem cell therapy

Researchers have been investigating whether stem cell therapy can regenerate cartilage in people with OA.

However, a number of challenges remain. For example, the therapy is expensive, a person may have to receive several rounds before they see results, and the treatment may be ineffective if a person’s body mass index is over 35.

Authors of a 2018 meta-analysis looked at ways of using stem cells to treat OA and how this influenced long-term results. They concluded that the findings of high quality studies were inconsistent.

Some clinics offer stem cell therapy for OA, but the Food and Drug Administration (FDA) warned the public in 2017 not to “believe the hype.”

The ACR and AF strongly recommend against using stem cell therapy, as there are no standards to regulate this practice.

Side effects of unapproved stem cell treatments may include:

  • adverse reactions at the site of the injection
  • cells reproducing in the wrong location
  • failure of the cells to work as expected
  • a risk of tumors

Anyone considering stem cell treatment for OA should contact a doctor first.

OA of the knee is a progressive condition in which cartilage breaks down around the bones in a joint.

As time goes on, the bones will start to rub together, and bone spurs can develop. There will be increasing levels of pain and stiffness and possibly a loss of mobility.

Various treatment options can help manage OA. A doctor will recommend treatment type depending on individual needs and the stage of OA a person is experiencing.