Knee MRI (with contrast)

What it is

A meniscus that has been operated on never looks normal again. The remaining rim carries scar and altered signal for years, and on a standard MRI that looks a great deal like a new tear — which is why a plain scan of a previously operated knee is one of the harder reads in musculoskeletal imaging. Filling the joint with a dilute gadolinium solution changes the problem. Fluid under gentle pressure tracks into a genuine defect and stops at scar, so a split that has actually opened up is outlined and old surgical change is not. The injection is done first, by a radiologist using x-ray or ultrasound to guide the needle into the joint, and the scan follows. Because imaging happens only after contrast, the study bills as a with-contrast knee MRI, with the injection and the guidance charged on their own.

Why it is done

• To distinguish a new meniscal tear from post-surgical scar in a knee that has already had meniscal surgery
• To look at a cartilage repair or transplant and see whether it has taken and sealed at its edges
• To check whether a fragment of cartilage or bone has separated from the joint surface, and whether fluid has undercut it
• To answer a specific question ahead of revision surgery, where the surgeon needs to know what is intact before going back in

What to expect

Two stages in one visit. First the injection: the knee is cleaned, the skin numbed, a needle placed into the joint and the solution injected under guidance. Most people describe tightness and fullness rather than pain, sometimes with a sensation of the knee being hard to fully bend. Then the MRI, usually within the next half hour, so the joint is imaged while still distended. The scan itself is no longer than a standard knee study. The fullness eases over a day, aching afterward is common, and strenuous use of the knee is normally deferred until it settles.

Questions worth asking

• Ask for an itemized estimate covering three separate services: the joint injection, the imaging guidance for the needle, and the MRI.
• The radiologist performing the injection and the one reading the scan may bill under different entities. Confirm both are contracted with your plan.
• Ask whether your insurer treats an arthrogram as requiring its own prior authorization on top of the MRI approval.
• If your knee has been operated on before, ask whether a plain scan was considered first and why it was not judged sufficient — the answer changes the price considerably.
• Ask what is billed if the joint cannot be entered and the appointment ends as a plain scan.