Knee MRI (without contrast)

What it is

A knee that locks, gives way, swells after a twist, or hurts along one joint line is telling you something is torn, but not what. The structures at issue are all soft tissue — two C-shaped shock absorbers called menisci, the cruciate ligaments crossing in the middle, the collateral ligaments at the sides, the tendons, and the layer of cartilage on the ends of the bones. None of them appear on an x-ray. This scan shows all of them, in slices through several planes, and no injection is needed: an injured knee usually has extra fluid in it already, and that fluid outlines the surfaces well enough. It is the single most commonly ordered joint MRI, largely because its answer is actionable — a torn meniscus that is trapped in the joint is managed very differently from one that is not.

Why it is done

• To confirm or rule out a meniscal tear in a knee that catches, locks or gives way
• To assess a cruciate or collateral ligament after a twisting injury or a blow to the side of the knee
• To look at the cartilage surfaces, and at bone bruising underneath them, after trauma
• To find a fracture that plain films did not show, or an area of bone that has lost its blood supply
• To investigate swelling, effusion, or pain that has persisted without an obvious cause
• To map the damage before an arthroscopy or a reconstruction

What to expect

There is no preparation and nothing to swallow or inject. After metal screening, the leg is settled into a padded coil with the knee slightly bent and held still with straps — the strapping is there because even small movements blur the thin slices this study relies on. You go in feet first, which means the head usually stays outside or near the opening of the tube, and many people who dread MRI find a knee scan much easier than they expected. It takes roughly twenty to forty-five minutes and is loud throughout. You can walk out and drive. The images go to a radiologist, and the report generally reaches the ordering doctor within a few days.

Questions worth asking

• Ask whether your plan requires prior authorization for knee MRI, and whether it expects a period of conservative treatment to be documented first.
• Many orthopedic groups now have a scanner in the building. Ask what that site charges against the hospital radiology department, since for an unenhanced extremity scan the gap is often large.
• Ask whether the quoted price includes the radiologist's reading or only the scan, and whether the reading group is in your network.
• Ask for the images on disc or through a portal. A surgical second opinion should not require paying for the scan twice.
• If both knees are symptomatic, confirm what was ordered. Each knee is its own code and its own charge.