Diagnosing Osteoarthritis

A diagnosis of osteoarthritis is made with:

• A medical history and physical examination

• Imaging methods

• Laboratory tests

Physical Examination

A primary care physician or rheumatologist (specialist in rheumatic disorders of the joints and related structures) will ask about:

• Joint symptoms

• Previous or current illnesses

• Traumatic injuries

• Operations you may have had

• Allergies

• Other medical conditions

The physician will inspect the affected joint(s), checking for swelling, redness and heat, tender points, skin rashes, and other bodily signs. Determining which joints are involved and how their function is impaired helps the physician to distinguish OA from other forms of arthritis.

The muscles that surround painful, underused joints may show signs of weakness. The pattern of arthritis in the hands may be especially helpful in the diagnosis. OA tends to involve the base of the thumb and the middle and end joints of the digits.

Imaging Methods

X-rays will confirm the diagnosis of arthritis but will not necessarily indicate the type of arthritis. The physician will look for specific structural changes in the joint(s) that suggest OA, such as:

• Narrowing of the joint space. This occurs due to loss of cartilage (for example, joint space narrowing of the inside half of the knee).

• Bony spurs. These are outgrowths of new bone called osteophytes that develop at the margin of the joint. It is nature's way of protecting the joint.

• One-sided distribution (for example, one knee, one hip) of joint irregularities.

• Cysts. These may be seen in the bone just beneath the joint surfaces.

By contrast, imaging studies in people with rheumatoid arthritis more often show

• Loss of calcium from the bone (localized bony decalcification)

• Erosion-producing defects or holes in the bones in a joint

• Changes in many joints on both sides of the body, particularly the hands and wrists

Laboratory Tests

If there is a question about the exact nature of joint swelling, the physician may perform a joint aspiration. During this procedure:

• A needle is gently inserted into the joint to withdraw a small amount of synovial fluid from the joint.

• The fluid then is tested for chemistry, viscosity (thickness), blood cell counts, overall appearance, and microorganisms (if an infection is suspected).

• The fluid from an OA joint is usually clear, whereas in RA, it is cloudy due to the presence of many white blood cells.

• The fluid then is tested for crystals to exclude such diagnoses as gout.

• Sometimes the fluid from an OA joint contains calcium pyrophosphate crystals, which may cause mild irritation and increase swelling.

Blood tests may be ordered in puzzling cases to identify infection, measure blood cell counts, and pinpoint telltale diagnostic findings such as rheumatoid factor (RF) and human leukocyte antigen (HLA-DR4 and HLA-DR1), which are more common in people with inflammatory types of arthritis such as rheumatoid arthritis.

Blood and urine tests may be ordered to rule out conditions such as gout. The blood from people with gout contains a high level of uric acid, which is associated with the buildup of arthritis-causing crystals in the joint fluid.