Aims: The most common complications after total knee arthroplasty (TKA) are the result of patellar complications. The causes of patellar problems range from sub-luxation, dislocation, component loosening, rupture of the patellar tendon, excess wear of the polyethylene (especially after metal backing), retropatellar pain, and patellar fracture. The incidence of these patellar complications after TKA ranges from 5–30%. Selective retention of the patella has been recommended more recently although there are still potential problems of maltracking and anterior knee pain. According to the nationwide registration of all TKAs in Finland since 1980 it seems evident that interest of patellar retention during the primary operation has now been stabilized at the level of about 55 per cent. At the same time there are, however, quite a high incidence of reoperations done due to patellar complications or later resurfacing of the patella in connection of revisions done with other indications. Methos:

Database of the Finnish Arthroplasty Register was evaluated from the years 1999 and 2000 focusing on the reoperations done either due to patellar complication (in the notiþcation: indication for revision) or due to other reason (to be speciþed in full text). These were further divided into three main categories: removal or fracture of patellae, delayed resurfacing due to patellar pain or maltracking, and component loosening.

Conclusions: Reoperations done due to the patellar complications and/or later resurfacing of patellae mean quite a notable work-load; 31,7 to 33,6 per cent of all TKA revisions done in the years 1999 and 2000, respectively. Of the total of 113 delayed patellar resurfacing operations, almost 50 per cent were done in connection to revisions primarily due to other reasons, usually after excess liner wear. In conclusion we can say, that ÒprimaryÒ patellar complications (after patellar resurfacing in the primary operation) encountered about 15 per cent of all revisions, and those done in the Òsecondary phaseÒ (after retention of patella) another 15 to 16 per cent. This is in accordance with the results gained in the other Nordic Registers; in Norway ÒprimaryÒ/loose 16,5% of all TKA revisions. It seems that the need for a secondary patellar replacement in unreplaced cases was balanced by the need for revisions of failed patellar components in patellar replaced cases.