Diagnosis:

Osteoarthritis is often visible in x-rays. Cartilage loss is suggested by certain characteristics of the images:

• The normal space between the bones in a joint is narrowed.
• There is an abnormal increase in bone density.
• Bony projections, cysts, or erosions are visible.

If the doctor suspects other conditions, or if the diagnosis is uncertain, additional tests are necessary.

It is important to note that a negative x-ray does not rule out osteoarthritis. Likewise, some people may have minimal symptoms even though an x-ray clearly shows they have arthritis.

An MRI exam of an arthritic joint is generally not needed, unless the doctor suspects other causes of pain.

X-rays are a form of ionizing radiation that can penetrate the body to form an image on film. Structures that are dense (such as bone) will appear white, air will be black, and other structures will be shades of gray depending on density. X-rays can provide information about obstructions, tumors, and other diseases, especially when coupled with the use of barium and air contrast within the bowel.

Physical Exam

The affected joint in patients with osteoarthritis will generally be tender to pressure right along the joint line. Joint movement may cause a crackling sound. The bones around the joints may feel larger than normal. The joint's range of motion is often reduced, and normal movement is often painful.

Blood Tests

Blood test results may help identify other causes of arthritis (if present) besides osteoarthritis. Some examples include:

• Elevated levels of rheumatoid factor (specific antibodies in the synovium) are usually found in patients with rheumatoid arthritis
• The erythrocyte sedimentation rates (ESR, or "sed rate") indicates inflammatory arthritis or related conditions, such as rheumatoid arthritis or systemic lupus erythematosus.
• Elevated uric acid levels in the blood may indicate gout.

A number of other blood tests may help identify other rheumatological illnesses.

Tests of the Synovial Fluid

If the diagnosis is uncertain or infection is suspected, a doctor may attempt to withdraw synovial fluid from the joint using a needle. There will not be enough fluid to withdraw if the joint is normal. If the doctor can withdraw fluid, problems are likely, and the fluid will be tested for factors that might confirm or rule out osteoarthritis:

• Cartilage cells in the fluid are signs of osteoarthritis.
• A high white blood cell count is a sign of infection, gout, pseudogout, or rheumatoid arthritis.
• Uric acid crystals in the fluid are an indication of gout.

• Other factors may be present that suggest different arthritic conditions, including Lyme disease and rheumatoid arthritis.
• In people with known osteoarthritis, researchers may look for certain factors in synovial fluid (sulfated glycosaminoglycan, keratin sulfate, and link protein) that can suggest a more or less severe condition.

Ruling Out Conditions with Similar Symptoms

Numerous conditions cause symptoms of joint aches and pains. Something as simple as sleeping on a bad mattress or as serious as cancer can mirror symptoms of osteoarthritis. Other problems that can cause aches and pains in the joints include physical injuries, infections, tendinitis, and poor circulation.

Osteoarthritis can generally be distinguished from other joint diseases by considering several factors together:

• Osteoarthritis usually occurs in older people and is located in only one or a few joints.
• The joints are less inflamed than in other arthritic conditions.
• Progression of pain is usually gradual.

Below are a few of the most common disorders that can be confused with, or may even accompany, osteoarthritis.

Rheumatoid Arthritis. Osteoarthritis can be confused at times with milder forms of rheumatoid arthritis, particularly when osteoarthritis affects multiple joints in the body. It normally occurs earlier in life than osteoarthritis, often striking people in their 30s and 40s. Rheumatoid arthritis affects many joints, and often occurs symmetrically on both sides of the body. People with rheumatoid arthritis generally have morning stiffness that lasts for at least an hour. (Stiffness from osteoarthritis usually clears up within half an hour.) Although osteoarthritis can occasionally cause swollen, red joints, this appearance is much more typical of rheumatoid arthritis and other types of inflammatory arthritis. In addition to blood tests, x-rays can help show differences between rheumatoid arthritis and osteoarthritis.

Rheumatoid arthritis is a body-wide (systemic) autoimmune disease that initially attacks the synovium, a connective tissue membrane that lines the cavity between joints and secretes a lubricating fluid.

Chondrocalcinosis (Pseudogout). Chondrocalcinosis (pseudogout syndrome) is a disease in which a certain type of calcium crystals known as CPPD (calcium pyrophosphate dihydrate) accumulate in the joints. This condition affects about 25% of the population and can accompany and even worsen osteoarthritis. Chondrocalcinosis is also called pseudogout or pseudo-osteoarthritis, the latter particularly when it affects the knees. A doctor can usually differentiate between the two disorders because chondrocalcinosis usually damages other joints (such as wrists, elbows, and shoulders) that are not normally affected by osteoarthritis.

Charcot's Joint. Charcot's joint occurs when an underlying disease, usually diabetes, causes nerve damage in the joint, which leads to swelling, bleeding, increased temperature, and changes in bone. There may be a loss of sensation that leads to an increased risk of injury from overuse.