73721 CPT code: description, billing rules, and 2026 payment rates

Anyone who bills for an orthopedic group, a freestanding imaging center, or a hospital radiology department sees the 73721 CPT code on claims almost daily. It reports MRI of any joint of the lower extremity performed without contrast, which makes it the default code for knee, hip, ankle, and foot joint imaging. Revenue cycle firms that track Part B utilization estimate Medicare processes roughly four million claims a year for this single code.

The code itself is simple. The denials it generates usually trace back to four specific mistakes: a missing laterality modifier, contrast that was injected into the joint rather than a vein, a study that belonged under the non-joint code 73718, or a skipped prior authorization. This guide works through the official description, the anatomy the code covers, the related codes worth memorizing, modifier rules, and what the procedure pays in 2026.

What is CPT code 73721?

The American Medical Association defines CPT 73721 as: “Magnetic resonance (eg, proton) imaging, any joint of lower extremity; without contrast material.”

The code sits in the diagnostic radiology section of the CPT manual, within the 73700 series covering the lower extremities. Three phrases in that descriptor carry all the billing weight.

“Any joint” means one code serves four anatomic regions. The hip, the knee, the ankle, and the joints of the foot all map to the same five digits. CPT publishes no separate code per joint, which surprises coders coming from the X-ray codes, where the knee and ankle each have their own series.

“Without contrast material” excludes gadolinium by any route. That covers intravenous contrast and contrast injected directly into the joint during an arthrogram. If contrast enters the patient in connection with the study, 73721 no longer applies.

“Joint” is the third limiter. A study of the femoral shaft, the calf muscles, or a plantar soft tissue mass belongs to 73718, the code for lower extremity MRI other than joint.

MRI knee, ankle, hip, and foot: which studies map to code 73721

The knee produces most of the volume. Radiologists order non-contrast knee MRI to evaluate meniscal tears, ACL and PCL ruptures, collateral ligament sprains, cartilage defects, and occult fractures, and gadolinium adds no diagnostic value for those questions in a native knee. The MRI knee without contrast CPT code is therefore 73721, and laterality travels on a modifier rather than a different code:

• MRI right knee without contrast: 73721-RT
• MRI left knee without contrast: 73721-LT

Every other lower extremity joint follows the same pattern. The MRI ankle without contrast CPT code is 73721 with RT or LT. The MRI hip without contrast CPT code is 73721, commonly ordered for suspected labral tears, femoroacetabular impingement, occult femoral neck fractures, and avascular necrosis. A foot MRI takes 73721 when the clinical question centers on a joint (midfoot arthritis, a Lisfranc injury) and 73718 when it does not.

Bilateral studies use two claim lines. An MRI of both hips without contrast goes out as 73721-RT on one line and 73721-LT on a second.

Coders hunting for an MRI lower extremity without contrast CPT code have to settle the joint question first. A joint study is 73721; a thigh, lower leg, or non-joint foot study is 73718. Payer medical policies, including the Florida Blue coverage guideline for lower extremity MRI, print the two families side by side because they get swapped so often.

73721 CPT code description compared with related codes

Two traps in this family account for most audit findings.

The first is the arthrogram. Gadolinium injected into the joint space counts as contrast, so a direct MR arthrogram of the hip is reported with 73722, the joint injection code, and the applicable image guidance code (77002 for fluoroscopic guidance, or 77021 when needle placement happens under MR guidance). Reporting 73721 for an arthrogram undercodes the scan and strands the injection charge.

The second is the combined study. When the radiology report documents non-contrast sequences followed by contrast administration and further sequences, the entire encounter is 73723. Pairing 73721 with 73722 or 73723 for the same joint on the same date is a bundling error, and the coding education firm Coding Ahead lists the 73721/73723 combination as an active Recovery Audit Contractor review topic.

One housekeeping note: 72721 and 73321 are not valid CPT codes. Searches for either almost always mean 73721 itself or the upper extremity joint codes 73221 (without contrast) and 73222 (with contrast).

Does CPT code 73721 need a modifier?

Most claims carry at least one.

RT or LT belongs on essentially every claim, since auditors expect laterality modifiers on all extremity imaging. Medicare assigns 73721 a bilateral surgery indicator of 3, so modifier 50 and bilateral pricing logic do not apply; each side goes on its own line with RT or LT and pays at the full allowed amount. Some commercial payers still prefer modifier 50 for bilateral studies, so the payer manual decides.

Modifiers 26 and TC split the service when two entities are involved. A radiologist reading a hospital-performed study bills 73721-26 for the interpretation, the facility reports the technical component, and a freestanding center that owns the magnet and employs the interpreting physician bills the code globally with neither modifier.

CMS caps the code with a Medically Unlikely Edit of 3 units per date of service, enough for a knee, an ipsilateral ankle, and a contralateral joint on one day. Genuinely distinct same-day joints may need modifier 59 or XS depending on the payer’s edit logic.

CPT code 73721 cost and 2026 payment rates

The CY 2026 Medicare Physician Fee Schedule final rule, released October 31, 2025, set two conversion factors for the first time: $33.5675 for clinicians in qualifying alternative payment models and $33.4009 for everyone else. At the non-QP factor, the national non-facility global payment for 73721 works out to roughly $229.50, per ClaimMax RCM’s 2026 rate analysis. Geographic practice cost indices shift that figure by locality, and the CMS PFS Look-Up Tool returns the exact local amount.

Hospital outpatient departments are paid under a different system. The 2026 OPPS assigns 73721 to APC 5523 at $243.77 for the facility, with the radiologist’s interpretation billed separately under modifier 26.

For patients, Medicare.gov’s Procedure Price Lookup shows average beneficiary cost-sharing of about $66 for the study in outpatient settings. Commercial contracted rates typically run $250 to $400, with Blue Cross Blue Shield plans clustering between $275 and $350 in the same analysis. Contracted amounts vary enough that no practice should quote a patient from national figures.

ICD-10 pairing, indications, and coverage limits

Payment depends on a diagnosis that supports medical necessity. Codes frequently paired with 73721 include M25.561 and M25.562 (pain in the right or left knee), the M23.2 series (meniscus derangement), S83.511A and S83.512A (ACL sprain, initial encounter), and the M87.05 series (osteonecrosis of the femur).

Traditional Medicare imposes no prior authorization on outpatient MRI, though contractor local coverage determinations still govern necessity. Commercial plans are stricter. Most route advanced imaging through radiology benefit managers such as EviCore by Evernorth or Carelon, which generally expect documented conservative treatment before approving a joint MRI for uncomplicated pain. Requirements differ between plan types under the same carrier name, so verification against the member’s specific benefit tier prevents the CO-15 authorization denial that a clean claim cannot survive.

Frequently asked questions

What does CPT 73721 mean?

It is the AMA procedure code for MRI of any single joint of the lower extremity (hip, knee, ankle, or foot) performed without contrast material.

What CPT code is used for MRI of the right knee?

73721 with modifier RT, assuming no contrast was given. A left knee study is 73721-LT.

What is the cost of CPT code 73721?

About $229.50 under the 2026 Medicare non-facility fee schedule nationally, $243.77 to hospital outpatient departments under APC 5523, and roughly $250 to $400 under typical commercial contracts. Medicare patients pay around $66 on average.

When should CPT 73721 be used?

Whenever an MRI targets one lower extremity joint and no contrast is administered by any route. Non-joint anatomy shifts the claim to 73718.

Four checks before the claim goes out

The 73721 CPT code rewards a short pre-submission routine: confirm the study centered on a joint rather than surrounding anatomy, confirm no contrast entered the patient intravenously or intra-articularly, attach RT or LT, and verify the authorization on file matches the member’s actual plan. Those four checks eliminate nearly every denial this code produces.