Micromotion in Knee Arthroplasty. A Roentgen Stereophotogrammetric Analysis of Four Different Concepts of Prosthetic Fixation

摘要

In a prospective study, micromotion between tibial components and bone was analysed using roentgen stereophotogrammetric analysis (RSA), the potential of which was assessed. The patient material consisted of 96 arthrotic knees subjected to arthroplasty with six types of prostheses representing four different fixation concepts with and without bone cement. Provided stable conditions of the objects studied, RSA proved to have an accuracy (=resolution) of 0.3 degrees for rotation and 0.2 mm for translation (3 S.D.). This resolution was 10 times better than conventional radiography and sufficient for the study of micromotion. Micromotion, both gradual over time (migration) and instant, in response to applied forces (inducible displacement), was found for all tibial components studied. For conventional cemented prostheses the mean migration was 1-1.5 mm for the different groups. Most of the migration occurred during the first 6 months. Inducible displacement of 0.2-1.0 mm was found in most cases. Metal support did not improve the prosthetic fixation. For the non-cemented cases both migration and inducible displacement was significantly larger than in cemented cases. All prostheses proved to be bonded to the bone in a semi-rigid way permitting micromotion. The newer fixation concept did not prove superior to conventional cementing of all-polyethylene prostheses. The micromotion occurred within the soft tissue layer constituing the radiolucent zone, which in some cases was of tensile origin. Other radiographic clinical variables did not correlate with the micromotion. (Atomindex citation 16:074779)