Estimation of the migration of tibial components in total knee arthroplasty - A roentgen stereophotogrammetric analysis

Accurate quantitative measurements of micromovement immediately after opera tion would be a reliable indicator of the stability of an individual compon ent. We have therefore developed a system for measuring micromovement of th e tibial component using three non-contact displacement transducers attache d to the tibial cortex during total knee arthroplasty (TKA). Using this sys tem we measured the initial stability in 31 uncemented TKAs. All the tibial components were fixed by a stem and four screws. The initial stability was defined as the amount of displacement when a load of 20 kg was applied. Th e mean subsidence was 60.7 mu m and the mean lift-off was 103.3 mu m. We also studied the migration of the tibial component using roentgen stereo photogrammetric analysis (RSA) for up to two years after operation. Most mi gration occurred during the first six months, after which all prostheses re mained stable. We defined migration as the maximum total point motion (MTPM ) at two years after operation. The mean migration was 1.29 mm at two years . Our results show that there was a significant correlation between the initi al stability and migration (p < 0.05) and emphasise the importance of the i nitial stability of the tibial component.