Key Steps to assign codes for Total Knee Arthroplasty procedures

Knee arthroplasty is a common minimally-invasive surgery performed in orthopaedics. A proper understanding of the knee arthroplasty procedure and types such as initial or revision arthroplasty will surely help you in the assignment of correct codes.

What is Arthroplasty?

It describes the surgical replacement or reconstruction of a joint with implanted devices when the joint has been damaged by an arthritic or traumatic process.

What is total knee arthroplasty? (TKA)

A total knee arthroplasty is a surgical procedure whereby the diseased knee joint is replaced with the artificial material. The procedure involves cutting away damaged bone and cartilage from the thighbone (femur), shinbone (tibia) and kneecap and replacing it with an artificial joint (prosthesis) made of metal alloys, high-grade plastics and polymers.

Primary reason for total knee arthroplasty:

Knee replacement surgery is a treatment for pain and disability in the knee. The most common conditions that would result in the need for knee replacement surgery are listed below:

Osteoarthritis: This is an age-related “wear and tear” type of arthritis. The cartilage that cushions the bones of the knee softens and wears away. This causes the bones to rub against one another resulting in knee pain and stiffness.

Rheumatoid arthritis: This is a disease in which the synovial membrane that surrounds the joint becomes inflamed and thickened. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain and stiffness.

Post-traumatic arthritis: This can follow a serious knee injury. Fractures of the bones would damage the articular cartilage over time, causing knee pain and stiffness.

Procedure of Total Knee Arthroplasty:

There are four basic steps involved in a knee replacement procedure. The coders can verify all these steps in the medical record to select the appropriate codes for TKA.

1. Preparation of bone: The first step is to prepare the bones to make it fit for the insertion of prosthetic components. Basically, total knee replacement requires the use of three components listed as below:

  • Femoral component (to resurface the end of the thighbone)
  • Tibial component (to resurface the top of the tibia, or shin bone);
  • Patellar component (to resurface the bottom of the kneecap )

The femur, commonly known as the thigh bone is the first target bone of the surgeon. The damaged bone and cartilage from the end of the femur is cut and resurfaced to fit the first part of the artificial knee, the femoral component.

Next, the surgeon prepares the tibia or shin bone. The damaged bone and cartilage from the top of the tibia is cut and resurfaced to fit the tibial component of the total knee arthroplasty.

2. Prosthetic implants: The damaged surfaces of the knee joint is removed and resurfaced with the prosthetic components. The femoral component is mostly made of cobalt-chromium alloys. The tibial component is usually made of metal platform with a polyethylene (plastic) insert.

3. Patella resurfacing: A dome-shaped piece that replaces the damaged knee cap that rubs against thighbone. It is usually made of polyethylene (a durable plastic).

4. Insertion of spacer: A medical-grade plastic spacer is inserted between the tibial and femoral components to create a smooth gliding surface.

Figure: Steps involved in TKA procedure:

Types of Knee replacement Implants:

Coders can look for the below types of implants in the medical record as these are the most popular knee replacement parts manufacturers used by the surgeons for TKA.

  • Zimmer
  • Biomet
  • Stryker
  • Depuy
  • Smith & Nephew

Unicompartmental Knee Arthroplasty OR Partial Knee Replacement:

Unicompartmental knee arthroplasty (UKA) is also called as partial, hemi- or unicondylar knee, bicondylar knee arthroplasty and involves the replacement of only one compartment. This procedure is mostly indicated for patients with predominantly Unicompartmental arthritis.

During knee replacement surgery, damaged bone and cartilage is resurfaced with metal and plastic components. In unicompartmental knee replacement (also called “partial” knee replacement) only a portion of the knee is resurfaced. This procedure is an alternative to total knee replacement for patients whose disease is limited to just one area of the knee.

Revision Arthroplasty:

Revision arthroplasty requires the removal of previously placed prosthetic components and reinsertion of new components in a single surgical procedure. Removal of the previously inserted prosthesis is included in the code.

During primary total knee replacement, the knee joint is replaced with an implant, or prosthesis, made of metal and plastic components. Although most total knee replacements are very successful, over time problems such as implant wear and loosening may require a revision procedure to replace the original components.

CPT directs the coders to use the revision codes based on the number of components being revised in the encounter.

  • If the failure of total knee arthroplasty requires a revision to only one component, use 27486
  • If the failure of total knee arthroplasty requires a revision to all components (femoral and tibial), use 27487

The major reasons for Revision of Total Knee replacement are as follows:

  • Implant loosening and wear
  • Infection of the artificial joint
  • Instability of the components
  • Fractures

Answering all the below questions would definitely help coders to select the appropriate codes for knee arthroplasty procedure.

1. Is the procedure an initial or revision arthroplasty?

2. Is this a total or partial replacement?

3. If partial, which compartment is replaced?

4. For revisions, is it one compartment or all components?


A modifier is needed to indicate which knee was affected. The claims submitted without the appropriate use of modifier can lead to denials by the payor considering being duplicate claims if the patient had any previous knee replacement.

LT – Added to the CPT to indicate the procedure was performed on the left knee.

RT – Added to the CPT to indicate the procedure was performed on the right knee.

50 – To indicate the bilateral procedure was performed.

CPT codes for reference are listed in the below table:

Happy learning ! Happy coding !


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