Your query lacks sufficient detail or content to be very helpful, such as the Operative Report containing the Preoperative evaluation of the patient and indications for surgery, the Postoperative Diagnosis, and the Description of the Procedure. Your note indicates that the patient had an infected arthroplasty for which the Arthroscopic Surgical lavage was done to "wash out" the joint, 29871 (the primary procedure). From there comes the issue of the patellar component. Was it entirely loose and free in the joint, acting as a Loose Body (or as a surgically implanted Foreign Body if you prefer)? If so, then the coding could be supplemented by 29874 with the appropriate Modifier(s) 22 or 51 or both. If the Patellar component was just loose on the patella, but not fully free from it, then there would have been some extra work involved in freeing it from the patella for removal from the joint. The indications for doing this would need to be in the Operative Report somewhere as this applies to Clinical Judgement (Medical Necessity) for removing it. I would still use 29874 for this as well with Modifiers as above. I don't think that a "modified" 27488: Removal of Prosthesis ..., as described in CPT, would be the best or correct for removal of the Patellar Component alone. Your Diagnosis codes would have to include the Infection of a joint prosthesis (T84.5 _X _, with 5th Character 3 for right, 4 for left knee, and 7th Character A since this is the Initial Treatment for the joint infection), and T84.03 _ _ (6th Character 2 for right knee, 3 for left knee, and A for 7th Character) for the Mechanical Loosening of the Patellar Component. As always for something this unusual, send the Operative Report with the claim.
Hopefully this will be of some help.
Respectfully submitted, Alan Pechacek, M.D.