Medium-term results of a mobile bearing total knee replacement.

Mobile bearing total knee arthroplasty kinematically allows the advantages of large and congruent surface contact and low contact pressures, while preserving flexion, extension, and rotation in knee motion. In allowing for these degrees of freedom, the interface between bone and component also is protected from high stress. The Self Aligning I total knee arthroplasty initially was implanted in patients after its development at the authors' institution in 1990. Between 1990 and 1994, 141 patients with osteoarthritis of the knee underwent 172 total knee replacements using this system. At average followup of 5.6 years (range, 5-8 years), clinical results using this system showed a 94% satisfaction rate (good or very good). Two revision surgeries have been performed for polyethylene wear, with none of the remaining knees showing evidence of discernible wear. Complications included four cases of deep infection, four cases where a press fit femoral component failed (nonporous coated) and the patients required revision surgery, four traumatic fractures (three patellar and one supracondylar), one popliteal artery occlusion, and one revision for stiffness. Three patients required manipulation under anesthesia for arthrofibrosis. Kaplan-Meier survival curves show the probability of survival to be 91.7%, with revision surgery for any reason as an end point, and 98.8% for revision surgery because of polyethylene wear as an end point. Following the initial learning curve with this prosthesis, the medium term results using this system show maintenance of clinical success. No progressive evidence of polyethylene wear with time has been found, supporting the concept of mobile bearing arthroplasty in extending the service life of total knee arthroplasty.