While many coders are familiar with unicompartmental (UKA) and total (TKA) knee arthroplasty procedures there are a couple of different coding scenarios that may leave you scratching your head.
The patient underwent a MEDIAL unicompartmental knee replacement five years ago. Due to progressive ongoing degenerative symptoms the patient now presents for a LATERAL unicompartmental arthroplasty on the same knee. This does not make the procedure a total knee or conversion to total knee arthroplasty. This is sometimes referred to as a bi-unicompartmental arthroplasty representing a UKA in both the medial and lateral compartments and the new procedure should be reported with CPT code 27446 Arthroplasty, knee, condyle and plateau; medial OR lateral compartment.
When the patient has had a previous partial knee replacement (UKA) and presents for a revision procedure you should report 27599 Unlisted procedure; femur or knee because the only revision codes available are for “total” knee replacements. This also applies to replacement of the tibial liner. You would not report 27486 with modifier -52 because 27486 represents a revision of total knee arthroplasty.