Diagnosing Osteoarthritis

The right diagnosis is essential in obtaining the right care. This involves a complete physical examination as well as radiological examinations and laboratory tests.

The Physical Examination

Diagnosing osteoarthritis begins with an in-depth evaluation by your physician, including a history and physical examination. Your physician will assess:

• Pain levels
• Joint range of motion
• Muscle strength in the affected region
• Presence of any swelling or tenderness of the joint
• Gait (the way you walk) if OA is in the hip or knee

Radiological Examination

X-rays are very helpful in diagnosing osteoarthritis because the affected joint will have a characteristic appearance, such as:

• Bones appearing closer to each other:  As cartilage wears away, the joint space can narrow.
• Cysts:  As the body responds to cartilage destruction and attempts to stabilize the joint, cysts or fluid-filled cavities can form in the bone.
• Increased bone density or uneven joints:  When bones are no longer cushioned by cartilage, they can rub against one another, creating friction. The body responds by laying down more bone in response, increasing bone density. Increased bone creates uneven joint surfaces and osteophytes (bone spurs) around the joint margins.

Osteoarthritis of the right hip with supralateral joint space narrowing - click to enlarge

Severe supralateral joint space narrowing and large osteophytes - click to enlarge

Earlier Diagnosis Through Imaging at HSS

Hospital for Special Surgery has developed special x-ray views that increase the sensitivity of conventional x-rays, allowing detection of early changes in the joint before they are evident on routine x-rays,

In some cases, specialized diagnostic imaging examinations are also used because they are more sensitive for the detection of early arthritis. These tests include MRI, CT, Ultrasound and Radionuclide Bone Scans.

• MRI (magnetic resonance imaging) is very sensitive to bony and soft tissue changes when dedicated protocols for the musculoskeletal system are used. MRI can demonstrate reactive bone edema or soft tissue swelling as well as small cartilage or bone fragments in the joint. At HSS, specific computer programs are used to identify early evidence of cartilage degeneration. When there is objective evidence of cartilage wear, appropriate treatment can be initiated to prevent or delay progression.

click to enlarge

MR - Axial plane of the hip demonstrating anterior joint narrowing and osteophytes around the femoral head - click to enlarge

MR - Coronal Plane of the hip demonstrating osteoarthritis with large osteophytes around the femoral head - click to enlarge

• CT (computed tomography) examinations are excellent for demonstrating the degree of osteophyte (bone spur) formation and its relationship to the adjacent soft tissues. CT examinations are also useful in providing guidance for therapeutic and diagnostic procedures.
• Ultrasound is extremely sensitive for identifying synovial cysts that can form in association with osteoarthritis. Ultrasound can also be used to image articular cartilage in patients who cannot tolerate an MRI examination because of claustrophobia or pacemakers. Ultrasound can also be used to provide guidance for diagnostic and therapeutic procedures.
• Radionuclide Nuclear Medicine Bone Scans are very sensitive in detecting reactive bone turnover association with osteoarthritis. Bone Scans can also image the entire skeleton in one examination and thus can provide the clinician with helpful information in patients in whom there may be multiple areas where OA is present.

For more information about medical imaging, please visit the HSS Department of Radiology and Imaging.

Laboratory Findings

Laboratory tests are helpful in the diagnosis of OA because they are usually normal. Routine tests such as complete blood counts, urinalysis, sedimentation rate (ESR), biochemistries, and specialized tests such as rheumatoid factor and antinuclear antibody (ANA) are useful simply to rule out other diseases that cause joint pain.

However, it should be remembered that as we age, a low level positive test for rheumatoid arthritis (rheumatoid factor) or ANA, and elevations of sedimentation rate (ESR) can sometimes develop without the presence ofthe illness. Although these findings can sometimes be confusing to a patient, they need not be. The clinical picture makes the diagnosis; lab tests are used only to confirm the clinical picture. Laboratory tests should never be used alone to diagnose arthritis.

Synovial fluid is the liquid that is normally found within the joints. It helps nourish and lubricate the joints. It is usually present in only very small amounts. However when arthritis is present, it changes in character and amount. Withdrawing the fluid can reduce swelling and pain.  It can also help to confirm the diagnosis.

When synovial fluid is removed, it should be sent for culture, well as tested for cell count. In osteoarthritis, the white cell count (“pus cells”) is usually low and the fluid is clear (like water); higher counts should suggest inflammatory arthritis or infection.

The fluid may also be examined for the presence of uric acid crystals (seen in gout) or calcium pyrophosphate crystals (seen in pseudogout or chondrocalcinosis). The measurement of other biological markers is still experimental.