Micromotion of conventionally cemented all-polyethylene tibial components in total knee replacements. A roentgen stereophotogrammetric analysis of migration and inducible displacement.

Micromotion of the tibial component in 27 knee arthroplasties for gonarthrosis, three of which were regarded as failures for reasons other than mechanical loosening, was studied using high-resolution roentgen stereophotogrammetric analysis (RSA). Migration over time was found in all cases, ranging from 0.2 to 2.1 mm. The majority of the cases showed migration during the first year only, while a minority migrated continuously during the period studied. The latter group showed more migration even after 1 year. All cases showed inducible displacement in response to external forces, ranging from 0.2 to 1.0 mm. The micromotion correlated with the age of the patient but not with other demographic parameters. Alignment or component position did not correlate with the micromotion. All cases but one had developed a radiolucent zone, and it was concluded that the micromotion occurred in the soft tissue interface between bone and cement. Such micromotion is a normal finding in cemented tibial components in knee arthroplasty.