How are MRIs used to diagnose hip and knee problems?

Magnetic resonance imaging uses a strong magnet and radio waves to evaluate cartilage, soft tissues, and bone marrow. MRI is more expensive than computed tomography (CT) or standard x-rays, but it's the most accurate way to detect ligament damage, cartilage damage from arthritis, or tears in the cartilage or meniscus. A technique in which gadolinium (a metal dye) is injected into the hip joint before an MRI is highly accurate in detecting labral problems, such as labral tears. MRI is also used to evaluate a possible pelvic fracture, tumor, or lesions around the pelvis and hip.

During the exam, which lasts about 45 minutes, you lie on a scanning table that slowly moves you through the machine. (Many centers have smaller MRI machines that can focus on specific body parts, so if you're having your knee done you may only need to insert your knee.) For a hip exam, your feet may be taped together to keep your hips in the desired position. For a knee exam, a wedge may keep your knees at the desired angle. In some cases, the radiologist may inject a dye to obtain better images. You cannot have an MRI if you have a pacemaker, aneurysm clips, or certain other metal implants.