The influence of metal backing in unicompartmental tibial component fixation. An in vivo roentgen stereophotogrammetric analysis of micromotion.

The fixation of the tibial component in 36 patients with conventionally cemented unicompartmental knee arthroplasties for femorotibial gonarthrosis was studied using roentgen stereophotogrammetric analysis (RSA). Twenty-four tibial components were all-polyethylene while 12 were metal-backed. The follow-up was for 6 years. Significant migration was detected for all cases but two and ranged from 0.3 mm to 5.4 mm. The greater part of the migration occurred during the first 1-2 years, after which two-thirds of the prostheses remained stable. Seven all-polyethylene components were subjected to a stress examination after 1-2 years and displacement, induced by external forces, was found in all seven. A strong correlation was found between the extension of the radiolucent line and the migration. Otherwise, neither demographic, clinical, nor radiographic data correlated with the RSA results. In this study metal backing did not have any influence on prosthetic fixation as measured by RSA.