CPT Code 73721: Knee and Leg Joint MRI Without Contrast

CPT 73721 reports a magnetic resonance imaging (MRI) study of one joint of the leg, such as the knee or ankle, performed without contrast. If contrast is used, the study is reported with 73722 (with contrast) or 73723 (without contrast, then with contrast) instead. It is not a brain MRI code: brain MRI has its own codes, 70551 to 70553. Like most imaging codes, 73721 can be billed whole or split into a professional component (the radiologist's reading) and a technical component (the scanner, staff and supplies).

The rules below are Medicare's, from the CMS fee schedule files, the Medicare Claims Processing Manual and the National Correct Coding Initiative (NCCI) policy manual. Commercial plans and Medicare Advantage plans set their own policies, especially on prior authorization, so check the plan's policy for the date of service. Payment varies by payer and locality; for Medicare, use the Physician Fee Schedule look-up.

What does CPT 73721 cover, and which codes sit next to it?

73721 belongs to a family of MRI codes split by body area and by contrast use. Described in our own words:

All of these are active codes in the 2026 Medicare fee schedule (RVU26D). One study of one joint is one unit. When both knees are scanned on the same day, each side is reported for Medicare with the RT and LT modifiers, and the fee schedule's bilateral indicator for these codes means each side is priced on its own, without the surgical bilateral adjustment.

How do you choose between 73721, 73722 and 73723?

By what the radiology report says was done, not by what was ordered:

• No contrast at any point: 73721.
• Images taken only after contrast: 73722.
• Images taken before contrast and again after it: 73723.

If the order was for a study without contrast and the radiologist added contrast, the code follows the study performed, and the authorization may need to be updated (see below).

A few NCCI rules apply to contrast studies:

• Getting contrast into the vein, and the injection itself, are part of an MRI with contrast. Intravenous access and injection codes aren't reported separately.
• The contrast agent itself has its own HCPCS Level II code. Gadolinium-based agents sit in the A9575 to A9585 range, each with its own dose unit. Report the agent only if your practice bought it and the payer pays for it separately.
• Medicare's JW and JZ modifiers apply to separately payable drugs from single-dose containers, and CMS names contrast agents among them: JW on a separate line for any amount discarded, JZ when nothing was discarded.
• For MR arthrography of the knee, injecting contrast into the joint is a separate procedure with its own code (27369). Confirm which MRI code to pair with it in the CPT instructions.

How do the 26 and TC modifiers split an MRI?

In the 2026 fee schedule, 73721 carries PC/TC indicator 1: a diagnostic test with both a professional and a technical component.

• No modifier (global): one entity owns the equipment and provides the reading, as in most freestanding imaging centers.
• Modifier 26 (professional component only): the radiologist's interpretation and written report, billed by the reading physician when someone else owns the equipment.
• Modifier TC (technical component only): the equipment, staff and supplies, billed by the equipment owner when a separate physician reads the study.

For Medicare hospital patients, the hospital is paid for the technical component through its own payment system, and the physician bills only the professional component with modifier 26. The interpretation must include a written report. Each claim should match who actually did the work.

Are there payment reductions for multiple studies on the same day?

Yes, for Medicare. 73721 is subject to the multiple procedure payment reduction for diagnostic imaging (multiple procedure indicator 4). When it is billed in the same session on the same day with another imaging study that is also subject to the reduction, Medicare pays the highest-priced technical component in full and 50% of the technical component of each additional study. The professional component of each additional study is reduced by 5%. These percentages come from the RVU26D file documentation; check the current file each year.

Does MRI of the knee need prior authorization?

It depends on the plan:

• Original Medicare. CMS's appropriate use criteria program for advanced imaging, which would have required ordering physicians to consult imaging criteria, was paused and its regulations rescinded in the CY 2024 Physician Fee Schedule final rule.
• Commercial and Medicare Advantage plans. Many require prior authorization for MRI, and some hand that review to a radiology benefit manager. Each plan keeps its own list; check whether an authorization covers the specific study, side and contrast option.

Check authorization before the study is scheduled, and again if the protocol changes, for example if contrast is added.

Which diagnosis codes support a knee MRI?

The diagnosis comes from the order and the report, coded under the ICD-10-CM outpatient guidelines:

• When the order says "rule out" or "possible", code the signs or symptoms that prompted the study, such as M25.561 (pain in the right knee), not the suspected condition.
• When the radiologist has interpreted the study and the final report is available at the time of coding, code the confirmed diagnosis, such as S83.241A (other tear of the medial meniscus of the right knee, current injury, initial encounter) or M17.11 (primary osteoarthritis of the right knee).
• Match laterality to the side scanned, and use the 7th character that fits the stage of care for injury codes.

Where do 73721 claims go wrong?

• Wrong contrast code: the order said without contrast but the report shows contrast, or the other way round.
• Wrong component: a global claim from a practice that only read the study, or a missing 26 or TC modifier.
• Missing or mismatched authorization: no authorization, or one for a different side, study or contrast option.
• Diagnosis: a "rule out" condition coded as if confirmed, or laterality that doesn't match the side scanned.
• Both knees on one line without the side modifiers the payer expects.

For billing support with imaging claims, see Highview's imaging center billing service. For plain radiographs, see the guide to CPT codes for X-rays.

Sources

• CMS, PFS Relative Value Files, RVU26D: 2026 status of 73718–73723, 73221–73223, 70551–70553 and 27369; PC/TC indicator 1; multiple procedure indicator 4 and the imaging reductions; bilateral indicator 3.
• CMS, Medicare NCCI Policy Manual, Chapter 9 (radiology, effective January 1, 2026): separate codes for contrast options; vascular access and contrast administration included in MRI with contrast.
• CMS, Medicare Claims Processing Manual, Chapter 13, sections 20.1 and 20.2: professional and technical components, hospital patients.
• CMS, Medicare Claims Processing Manual, Chapter 17, section 40: JW and JZ modifiers, including contrast agents.
• CMS, HCPCS quarterly update (October 2026 file): gadolinium contrast codes A9575–A9585, modifiers 26, TC, JW and JZ.
• Federal Register, CY 2024 Physician Fee Schedule final rule, section III.J: pause of the appropriate use criteria program and rescission of 42 CFR 414.94.
• CMS and NCHS, ICD-10-CM Official Guidelines for Coding and Reporting, FY 2027, Section IV.H and IV.K: uncertain diagnoses and patients receiving diagnostic services only.
• CDC/NCHS, FY 2027 ICD-10-CM code descriptions: M25.561, S83.241A and M17.11.
• CMS, Search the Physician Fee Schedule.