Osteoarthritis (OA) of the knee affects the bones, the cartilage, and the 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 is soft, and it lines the joints. It produces fluid, called synovial fluid, for lubrication, and it supplies nutrients and oxygen to the cartilage.
As these functions break down, they no longer protect the bones of the knee joint, and bone damage occurs.
OA of the knee can cause pain and stiffness. The symptoms worsen over time.
In osteoarthritis of the knee, the cartilage breaks down and bone damage results. As the stages progress, pain and stiffness increase.
OA of the knee takes several years to develop, and it progresses in stages.
The condition can be hard to treat because symptoms may not appear until OA reaches an advanced stage.
People with OA of the knee should be on the lookout for any changes in symptoms and other indications that the condition is advancing.
Stage 1: Minor
Small lumps of bone called osteophytes may grow in the knee area. There may be slight damage to the cartilage.
There will be no apparent narrowing of the space between the bones to indicate that the cartilage is breaking down.
People with stage 1 OA are unlikely to feel pain or experience discomfort. The joint will appear normal on an X-ray.
Stage 2: Mild
During this stage, a person may start to notice symptoms, and doctors can see some signs of wear.
X-rays and other scans of the knee joints will clearly show more osteophyte growth, and the cartilage will begin to thin.
The space between the bones will still appear normal, but the area where the bones and the tissues meet will start to harden.
When the tissues harden, this makes the bone thicker and denser. A thin layer of bone will also develop beneath the cartilage in the joints.
The person may experience stiffness or joint pain. The area around the knee joint may start to feel particularly stiff and uncomfortable after a person has been sitting for extended periods.
Though there may be some minor damage, the bones are not rubbing or scraping against each other. Synovial fluid is present, and it helps to reduce friction and support the movement of the knee.
Stage 3: Moderate
The damage to the cartilage has progressed, the gap between the bones has narrowed, and X-rays will show cartilage loss.
Pain and discomfort may occur while performing daily activities, such as running, walking, kneeling, and bending. There may be early signs of joint inflammation.
As OA progresses, the cartilage will continue to thin and break down. The bones will respond by thickening and growing outward to form lumps.
The tissue that lines the joint will become inflamed, and it may produce extra synovial fluid, resulting in increased swelling. This is called synovitis, and it is commonly known as water on the knee.
Stage 4 - Severe
Knee replacement surgery may be the only option for late-stage OA of the knee.
This is the most advanced stage of OA, and the symptoms are very visible. The space between the bones in the joint has continued to narrow, causing the cartilage to break down further.
As a result, there is stiffness in the joint, constant inflammation, and less fluid around the joint. There is more friction in the joint and more significant pain and discomfort while moving.
X-rays will show bone on bone, meaning that either the cartilage has completely worn away or there is very little left.
The individual will likely develop more bone lumps and experience pain that is often intense during simple activities, such as walking.
In severe cases, the bones may become deformed and angulated because of asymmetric loss of cartilage.
At this stage, surgical treatment is often the only option.
An individual may not notice symptoms in the early stages of OA.
If a person has knee pain, the doctor will ask about personal and family medical histories. They will then perform a full physical examination and order diagnostic tests.
The doctor will also ask:
- when and where the person is experiencing pain and stiffness
- how this affects their daily life
- whether they are taking any medications
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.
MRI scans and joint fluid tests can help detect early signs of OA. The doctor may perform a joint aspiration, which involves removing some fluid with a needle and sending it to a laboratory for testing.
X-rays can also show damage to the joint.
Treatment options depend on the stage of OA and how quickly the condition is progressing.
Any symptoms are usually minor, and acetaminophens or other over-the-counter (OTC) medications can often relieve the pain.
Performing certain exercises can help to build strength and mobility.
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 relieve stress on the knee
At this stage, people with OA of the knee may need to change their daily activities to avoid pain.
Treatments can include:
- taking OTC pain relievers, such as acetaminophen
- taking prescription pain relievers, including oxycodone or codeine
- receiving injections of corticosteroids or hyaluronic acid
A doctor will administer three to five hyaluronic acid injections over 3–5 weeks. It can take time for results to show, but relief can last for 6 months.
The AAOS have questioned the use of corticosteroid and hyaluronic acid injections. The drugs can be costly, and long-term use of corticosteroids can lead to adverse effects.
At this stage, the cartilage has either significantly diminished or disappeared completely.
The person may need surgery to replace or realign the joint.
People may try the following:
- magnetic pulse therapy, though there is a lack of research to confirm its effectiveness
- lateral wedge insoles
- supplements of glucosamine, chondroitin, or both
- needle lavage, which involves inserting a needle into the joint and injecting a saline solution
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.
A 2018 meta-analysis looked at different ways doctors were 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 United States Food and Drug Administration (FDA) warned people in November 2017 not to "believe the hype."
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 speak to their doctor first.
Understanding knee osteoarthritis
OA of the knee develops when the cartilage in the knee joint wears away, leading to an overgrowth of the bone underneath. The cartilage becomes rough and breaks down, resulting in pain, swelling, and difficulty moving the joint.
OA can develop at any age, but it most frequently develops in people aged over 50 years, according to the American Academy of Orthopaedic Surgeons (AAOS).
The Arthritis Foundation report that half of all adults will develop OA at some time.
According to the AAOS, risk factors for OA include:
- increasing age
- previous joint injury
- overuse of the joint
- weak thigh muscles
- genetic factors
A person is likelier to develop OA if they have certain conditions, including hemochromatosis, acromegaly, and rheumatoid arthritis.
A number of factors may put a person at risk of developing OA. Making changes may not prevent the condition, but a person may be able to reduce their risk or keep OA from advancing.
Repetitive exercise can increase the risk of developing OA of the knee.
The Arthritis Foundation suggest the following:
Maintaining a healthful weight: Excess weight puts extra pressure on the knees. Over time, this contributes to wearing down the cartilage.
Extra fat can also cause the body to produce cytokines, a type of protein. This can lead to widespread inflammation, and it can change the way that cartilage cells work.
Controlling blood sugar: High glucose levels can affect the structure and function of cartilage, and diabetes increases the risk of inflammation and cartilage loss.
In the U.S., more than 50 percent of people with diabetes also have arthritis.
Exercising regularly: Moderate exercise can help the joints stay flexible, strengthen the muscles that support the knees, and reduce the risk of many health conditions.
It may help to garden, walk, or swim for 30 minutes at a time, five times a week.
Anyone who has not exercised for an extended period, possibly due to difficulties with mobility, should ask a medical professional for advice about how to start.
Reducing the risk of injury: Cartilage that sustains damage from an injury is more likely to develop arthritis later.
Reduce the risk of tripping in the home, wear shoes that fit well, and use protective gear while playing sports to prevent injury.
Undergoing posture and bone alignment tests: A gait analysis and other tests can help doctors to assess bone alignment and posture. Some sources suggest that these can affect a person's risk of developing OA.
Researchers say these changes do not occur until after the early stages of OA of the knee, and that they may be a result rather than a cause of the condition. However, they add that a better understanding of these changes might help prevent OA from progressing and help in treatment and rehabilitation.
Avoiding overuse: Some sports or professions involve repetitive motions of the knee joint, such as kneeling or squatting.
People who regularly lift more than 55 pounds may have an increased risk of OA. Jobs that put people at risk may include laying carpets and unloading trucks or ships.
Varying activities and getting enough rest between periods of work or exercise may help.
Getting help: To prevent OA from advancing, ask a doctor for advice about treatment and lifestyle changes when discomfort starts.
Eating a healthful diet, getting enough sleep, managing stress, and staying active all contribute to better overall well-being and a decreased risk of health issues, including OA.