Advice from the AAOS:
A single-stage procedure
When a total knee prosthesis is removed and replaced as the definitive procedure during the same operative session, it is considered knee revision surgery. This is reported using current procedural terminology (CPT) code 27487—Revision of total knee arthroplasty, with or without allograft; femoral and entire tibial component.
A 2-stage procedure
What happens when the surgery is not so straightforward and the procedure has to be done in stages? Assume a situation in which the surgeon removes a knee prosthesis and inserts cement or a prosthetic spacer at the time the implant is removed. If this procedure is performed outside the global period of the original surgery, it would be reported using code 27488—Removal of prosthesis, including total knee prosthesis, methylmethacrylate with or without insertion of spacer, knee.
Six weeks later, the same surgeon brings the patient back to the operating room to remove the spacer and replace it with the definitive knee prosthesis. This procedure would be reported using code 27447-58, 22—Arthroplasty, knee, condyle and plateau; medial AND lateral compartments with or without patella resurfacing (total knee arthroplasty).
Reporting either of these surgeries with the revision code 27487 would be incorrect because the CPT code that describes total knee revision surgery requires that the exchange to the definitive prosthesis be done in the same surgical session.