What Is Knee Osteoarthritis?

The knees are the joints most often affected by osteoarthritis (OA). Knee arthritis occurs when the cartilage in the knee breaks down, which can happen due to aging, being overweight, or injury, among other things. The disease process begins before symptoms—pain, stiffness, and motion restriction—are noticed. Because of this and the fact that knee osteoarthritis is a progressive disease, getting a diagnosis and proper treatment as early as possible is key.

More than 14 million Americans have knee osteoarthritis. It is the most common cause of musculoskeletal disability in the United States. About 13% of women and 10% of men age 60 and older have symptomatic knee osteoarthritis.

Symptoms

Knee osteoarthritis develops gradually over a period of time and typically goes unnoticed until it becomes symptomatic, most often causing:

• Pain in the knee (usually worse after activity or overuse)
• Joint stiffness
• Joint swelling (mild inflammation and warmth may also occur)
• Limited range of motion
• Popping or locking up of the knee

As knee osteoarthritis progresses, symptoms generally become more severe. Pain may become constant, rather than occur only when you're standing, walking, or physically active.

With advanced OA, crepitus (a grinding sensation) may become noticeable. There also may be visible joint deformity or a feeling that the knee is going to "give out."

Causes

Knee osteoarthritis is caused by the breakdown of cartilage, the protective tissue that allows the bones that form a joint to smoothly glide over each other. Eventually, the cartilage loss may be so severe there is essentially none left covering the ends of the bones in the knee joint (known as a bone-on-bone abnormality). Loose bodies in the joint space may also contribute to pain and stiffness.

The cartilage loss in knee osteoarthritis can be caused by:

• Aging
• A previous knee injury, such as a fracture, ligament tear, or meniscal injury, which can affect the alignment of the knee and leg, further promoting wear-and-tear
• Repetitive strain on the knee
• Genetic predisposition to cartilage abnormalities and knee osteoarthritis
• Obesity and overweight, which add stress and burden to the affected joint and increases in pro-inflammatory cytokines
• Problems with the subchondral bone (the bone layer underneath the cartilage in the knee)

Diagnosis

As is the case when any type of arthritis is suspected, the initial consultation with your healthcare provider begins with a discussion of your symptoms. The location of the pain and when it occurs will assist in the diagnosis of knee osteoarthritis:

• Pain at the front of the knee (the patellofemoral joint) is usually made worse by a long period of sitting, standing up from a low chair, climbing stairs, or coming down an incline.
• There is usually no pain behind the knee unless associated with a Baker's cyst.
• Knee pain may disrupt your sleep (in advanced cases).

A review of your medical history and a physical examination follow. Your healthcare provider will:

• Observe the affected knee for swelling, warmth, and deformity, which may point to osteoarthritis or other conditions
• Assess range of motion passively and actively
• Note if there is tenderness to the touch
• Watch you walk to check for changes in your gait and signs of increased pain with weight-bearing

You should also expect blood tests to rule out other types of arthritis and imaging studies to look for evidence of structural changes consistent with osteoarthritis and for the purposes of differential diagnosis.

X-rays are ordered first and if more detailed imaging is needed, magnetic resonance imaging (MRI) or a computed tomography (CT) scan may be ordered. The condition of the knee might also be viewed during arthroscopic knee surgery.

The examination and imaging studies will reveal which component of the knee is affected.

Treatment

Knee OA cannot be cured, but there are treatments to help manage the symptoms. In 2019, the American College of Rheumatology and the Arthritis Foundation updated their guidelines for treating and managing knee osteoarthritis. Treatments that are "strongly recommended" have more evidence of benefit than those that are "conditionally recommended."

Knee replacement surgery is used as last resort after conservative treatments have failed to produce an adequate response.

Note there are several treatments the ACR/AF strongly recommends against for knee osteoarthritis: glucosamine, chondroitin, bisphosphonates, hydroxychloroquine, biologic medications, stem cell injections, hyaluronic acid injections, platelet-rich plasma, and transcutaneous electrical stimulation (TENS).

The guidelines also conditionally recommend against a number of other treatments. Ultimately, you and your healthcare provider will consider the pros and cons of all options to determine which may be safe and effective for you.

A Word From Verywell

Gaining control of knee osteoarthritis requires that you recognize early symptoms and consult your healthcare provider to obtain an accurate diagnosis. Once diagnosed, stick with a regimen consisting of proven and effective treatment options. Protect your joints by paying strict attention to modifiable factors that may affect disease progression.