MRI Right Knee Without Contrast CPT Code: 73721 Guide

The CPT code for an MRI of the right knee without contrast is 73721 with the laterality modifier RT (e.g., 73721-RT). This code reports magnetic resonance imaging of any lower extremity joint—including the knee, hip, ankle, or foot—performed without contrast material. For a right knee study, the RT modifier is essential to indicate the side examined.

CPT 73721 is defined by the American Medical Association as: “Magnetic resonance (eg, proton) imaging, any joint of lower extremity; without contrast material.” The code is used when no contrast agent (such as gadolinium) is administered intravenously or injected into the joint. If contrast is used, different codes apply: 73722 for with contrast, and 73723 for without and with contrast.

What CPT 73721 Covers

CPT 73721 is a single code that applies to MRI of any joint in the lower extremity. This includes the knee, hip, ankle, and joints of the foot. The code is not specific to the knee; it is used for all lower extremity joints when no contrast is given. The laterality modifier (RT or LT) identifies which side was imaged.

According to a2zbillings.com, the code is the default for knee, hip, ankle, and foot joint imaging. It is one of the most frequently billed MRI codes.

When to Use 73721 vs. Other MRI Codes

Selecting the correct code depends on two factors: whether the study is of a joint or non-joint structure, and whether contrast was administered.

• 73721: MRI of any lower extremity joint without contrast.
• 73722: MRI of any lower extremity joint with contrast.
• 73723: MRI of any lower extremity joint without and with contrast.
• 73718: MRI of lower extremity other than joint (e.g., thigh, calf) without contrast.
• 73719: MRI of lower extremity other than joint with contrast.
• 73720: MRI of lower extremity other than joint without and with contrast.

For a knee MRI without contrast, 73721 is correct. If the study includes contrast, use 73722 or 73723. If the MRI is of the lower extremity but not a joint (e.g., a soft tissue mass in the thigh), use 73718. Avenue Billing Services emphasizes that the code is per joint, not per region, so each joint imaged must be billed separately.

Modifiers for 73721

Modifiers are critical for accurate billing and reimbursement. For a right knee MRI, the RT modifier is required. For a left knee, use LT. For bilateral studies, bill two separate lines: 73721-RT and 73721-LT. Medicare assigns a bilateral surgery indicator of 3, meaning modifier 50 is not used; each side is billed separately.

Other modifiers may apply:

• -26: Professional component (interpretation only) when the radiologist bills separately from the facility.
• -TC: Technical component (equipment and facility) when the facility bills separately.
• -59: Distinct procedural service, used when multiple procedures are performed on the same day and need to be identified as separate.

Prospect Healthcare Solutions notes that most insurers require prior authorization for MRI, especially non-emergency cases, so obtaining authorization before the scan is essential.

Documentation and Medical Necessity

Proper documentation is key to avoiding denials. The medical record should include:

• A physician order specifying MRI of the right knee without contrast.
• Clinical indication such as suspected meniscal tear, ligament injury, persistent pain, or occult fracture.
• Imaging protocol confirming no contrast was administered.
• Radiology report with detailed findings and diagnostic impression.

Diagnosis codes must support the medical necessity of the MRI. Common ICD-10 codes associated with 73721 include S83.511A (sprain of anterior cruciate ligament) and other codes for internal derangement of the knee. Avenue Billing Services warns that unspecified or weak diagnosis codes increase denial risk.

Reimbursement and Cost

The cost of an MRI of the knee without contrast varies widely. According to Prospect Healthcare Solutions, the out-of-pocket cost before insurance can range from $500 to $3,000 in the United States. The actual reimbursement depends on the payer, geographic location, and whether the service is billed globally or split into professional and technical components.

Medicare and other payers may have specific coverage policies. For example, some payers require conservative treatment (e.g., physical therapy) before approving an MRI. Always verify payer-specific guidelines.

Common Billing Errors to Avoid

Several errors can lead to claim denials or audits:

• Missing laterality modifier: Always append RT or LT.
• Using 73721 for an arthrogram: If contrast is injected into the joint, the correct code is 73722 (or 73723 if both phases are done), plus the injection and guidance codes.
• Using 73721 for non-joint imaging: For lower extremity MRI other than a joint, use 73718.
• Bundling errors: Do not report 73721 with 73722 or 73723 for the same joint on the same date.
• Lack of prior authorization: Many payers require it; failure to obtain can result in denial.

a2zbillings.com highlights that the 73721/73723 combination is an active Recovery Audit Contractor review topic, so careful coding is essential.

Frequently Asked Questions

Is CPT 73721 the same as a knee MRI?

Yes, 73721 is the code for an MRI of the knee without contrast. However, it also covers other lower extremity joints, so the laterality modifier and documentation must specify the knee.

Can you do a knee MRI without contrast?

Yes, many knee MRIs are performed without contrast because gadolinium is not needed to evaluate meniscal tears, ligament injuries, and cartilage defects. Contrast is typically reserved for cases of suspected tumor, infection, or post-surgical evaluation.

What is the difference between 73721 and 73718?

73721 is for MRI of a lower extremity joint (knee, hip, ankle, foot joint) without contrast. 73718 is for MRI of the lower extremity other than a joint (e.g., thigh, calf, non-joint foot) without contrast.

What is the CPT code for MRI right knee without contrast in 2026?

The code remains 73721 with modifier RT. CPT codes are updated annually, but 73721 has been stable for many years. Always verify with the current year's CPT manual.

For more detailed billing guidance, refer to ClaimMax RCM and Medicotech for comprehensive lists of MRI CPT codes.