Finding the Right ICD-10 Code For Total Knee Replacement

As a rehab therapist, you’re getting plenty of patients through your door who are looking for help after a significant surgery. It’s your job to help create a recovery plan that gets them back to where they need to be to live a full and productive life. While you’re doing that, though, you’ve got to avoid your own pain point: incorrect coding. 

According to the American College of Rheumatology, there are about 790,000 total knee replacements (TKRs) per year, with that figure poised to rise as a significant portion of the American population continues to age. While physical therapy can help a patient manage their arthritis symptoms earlier in the process, just about every physical therapist in outpatient practice has seen their fair share of patients with the presence of an artificial joint. Here’s how you code for that treatment.  

What are some of the ICD-10 codes related to total knee replacement aftercare?

If we’re talking about patients coming in post-surgery, that means we’re talking about the aftercare codes—Z codes. While the patient’s total knee replacement may be due to underlying reasons, those reasons are likely considered no longer present and not why you’re treating the patient in this specific instance. As the ICD-10 coding guidelines state, “If the condition for which the rehabilitation service is being provided is no longer present, report the appropriate aftercare code as the first-listed or principal diagnosis.”

With that said, there are four specific Z codes that would apply to a patient with a total knee replacement:

• Z47.1: aftercare following joint replacement surgery;  
• Z96.651: presence of right artificial knee joint;
• Z96.652; presence of left artificial knee joint; and
• Z96.653: presence of artificial knee joint, bilateral.

At first glance, you might assume that the best codes to use for a patient with a total knee replacement would be the three codes under the Z96 category. However, using those three codes could land you in hot water. The answer to which code to use and when depends largely on acuity and the reason for the specific physical therapy episode of care.

Determining the Reason for PT in Patients s/p TKR

Receiving a total knee arthroplasty (synonymous with a TKR) involves a patient receiving an artificial knee joint. Having internal prosthetic devices implanted into your body is no easy feat—and I would argue a total knee arthroplasty (TKA) is perhaps one of the most brutal of surgeries. (Don’t believe me? I have seen an orthopedic surgeon take a full swing with a surgical hammer to get the prosthetic implant to fit, and the whole surgical table was shaking). For more proof, just ask anyone who has ever received a bilateral total knee arthroplasty—they’re tough, and the rehab is no joke either.

All this is to say that a patient often undergoes a TKR due to an external cause—more often than not, it is due to osteoarthritis, but a traumatic fracture could also be an external cause. That’s why the physical therapist needs to determine the reason for PT. If a patient has just come from surgery or their primary reason for PT is acute aftercare for a total knee replacement, then the code Z47.1 is the best-assigned code. Taken straight from the coding guidelines, “If a patient with severe degenerative osteoarthritis of the hip underwent hip replacement and the current encounter/admission is for rehabilitation, report code Z47.1, Aftercare following joint replacement surgery, as the first-listed or principal diagnosis.” The same can be said for a TKR. 

When to Use Z96 Classifications

According to the World Health Organization—which owns and publishes ICD-10-CM (the International Classification of Diseases, Tenth Revision, Clinical Modification)—the Z96 category is used for factors influencing health status that pertains to the presence of implanted prosthetics and other devices like an artificial knee joint. 

The key differentiator between Z96 and Z47.1 is the presence versus aftercare distinction. In general, if a patient had a TKR and completed rehabilitation for it but continued to have dysfunction or chronic pain beyond the normal course of care, then the Z96 codes would be better used in those instances. For a left knee replacement, use Z96.652. For the right, use Z96.651. For bilateral total knee arthroplasty, use Z96.653. 

There are reasons that are just chronic pain as to why a patient may be returning to PT for rehab following a TKR (like swelling or difficulty walking), but if the primary reason PT is due to the presence of the artificial knee joint, then these codes are best applied as the primary ICD-10 code.

Factors Influencing Health Status for Patients Needing TKR Rehab

For rehab involving an artificial knee joint, there are often additional health factors that could influence the PT plan of care and the patient’s prognosis. Something like chronic pain or prolonged difficulties with ambulation was noted previously, but what other factors might distinguish one patient from having chronic pain and one patient from having a stellar recovery? Perhaps two of the most important comorbidities to note are diabetes mellitus (Type 2) and hypertension. Both of these health factors could have a detrimental effect on the patient’s healing times and could very well determine if they might be affected by chronic pain in the future. As such, assigning them as a secondary diagnosis would be necessary to denote that additional therapeutic considerations are warranted for this patient to achieve an optimal rehab outcome.

Get More ICD-10 Coding Tips

If you want to learn more about the best ICD-10 codes to use, check out our blogs on CPT code 31575, CPT code 97535, and the latest updates to ICD-10 coding.

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