CPT Code 27599: Unlisted Procedure, Femur or Knee

Learn how CPT Code 27599 applies to unlisted femur or knee procedures, including documentation and billing guidelines.

What is an unlisted femur or knee procedure?

CPT code 27599 is an unlisted procedure code used when no existing CPT code accurately describes a surgical or non-surgical service performed on the femur or knee. This code applies to atypical, rare, or innovative procedures that are not yet categorized under specific Current Procedural Terminology listings.

Due to its nature, CPT code 27599 requires detailed documentation, justification of medical necessity, and a full description of the procedure performed. The American Medical Association designates this code for use when a physician must report a service related to the knee joint or femur that lacks a clearly defined procedural code.

CPT code 27599 documentation requirements

For proper use of the 27599 CPT code for other procedures for the femur and knee, the submission must include:

An attached operative report and detailed documentation supporting medical necessity, the patient’s condition, and the complexity involved in the surgical procedures.
A cover letter that explains the procedure performed, why a specific code does not apply, and a comparable CPT code for valuation.
The diagnosis and anatomical site involved (e.g., distal femur, patella, or knee joint).
A clear explanation of why an unlisted procedure code is used, such as when the technique or approach isn’t adequately described by CPT 27447, 27506, or other specific codes.
A comparable CPT code to aid valuation and reimbursement.
Any relevant device or implant descriptions used in the surgical procedures.
Supporting documents such as a physician’s statement, peer-reviewed literature, or references from CPT Assistant or the AMA to justify medical necessity and accurate billing.

This level of detailed documentation is crucial to prevent denials, support Medicare or commercial review, and ensure proper reimbursement for unlisted femur or knee services.

Billing guidelines

Billing CPT code 27599 requires manual review and pricing by the payer, as it is an unlisted procedure code without an assigned relative value. Always include:

Use of appropriate ICD-10 diagnosis codes and modifiers such as -RT (right) or -LT (left) when applicable to clarify the femur or knee site.
Note that the 27599 CPT code should not be reported alongside defined knee joint or femur CPT codes (like 27447 or 27506) unless the services are unrelated.
Preauthorization is typically required by many commercial insurance companies, especially for procedures involving open treatment, regional anesthesia, patellofemoral arthroplasty, or complex interventions. Medicare may require it in limited cases or under specific programs.

Following these billing and submission practices ensures accurate claims and reduces the risk of denials when using this unlisted code for femur or knee procedures.