Osteoarthritis (OA) is the most common articular disorder encountered worldwide. Its successful evaluation (and eventual treatment) depends on establishing a set of criteria for measuring disease progression. An ideal measurement would evaluate changes in articular cartilage, where the primary pathology of the disease takes place. Plain radiographs are the simplest and most readily employable means of joint evaluation, and now microfocal radiographs have been developed, which magnify the radiograph and help portray the joint space more accurately. However, radiography, along with nuclear medicine scans, arthrography, and computed tomography (CT) scans, are limited in their use because they are unable to detect early cartilage abnormalities. Magnetic resonance imaging (MRI) has the advantages of multiplanar imaging, soft tissue contrast, and noninvasiveness. Like radiography, MRI can underestimate the extent of cartilage abnormality. The most sensitive technique for measuring superficial articular abnormalities is arthroscopy, and small-bore arthroscopes are being used to assess knee damage in conscious, nonsedated patients. However, it is not yet clear if arthroscopy can detect subtle changes over time, and vision can be blocked by cloudy synovial fluid. Finally, although it is usually well tolerated, arthroscopy is an invasive technique.