Deformation and loosening of the tibial component in knee arthroplasty with unicompartmental endoprostheses.

Roentgenological signs of deformation and loosening of the tibial component in knee arthroplasties with unicompartmental endoprostheses occurred in one-third of 87 rheumatoid (RA) knees within 2 years and in one-fifth of 107 osteoarthritic (OA) knees within 3 years after the operation. Compared with thicker components significantly more 6 mm components in RA, and 6 and 9 mm components in OA became deformed and loose. There was no difference in the clinical assessment of the knees with and without deformed tibial components. Reoperations were recorded during an extended follow-up. In the group with initially asymptomatic loosening twelve RA knees within four and a half years and three OA knees within four years developed pain on weight-bearing and had to be reoperated. One patient (OA) had loose components without any roentgenological signs; the loosening was first discovered when the unoperated compartment was revised because of secondary osteoarthrosis. Knees fitted with 6 mm components more often required reoperation because of loosening than did those with thicker components.