Mobile-bearing total knee prosthesis : a 5- to 9-year follow-up of the first 110 consecutive arthroplasties

This study regards the total articulating cementless knee. This is a mobile-bearing knee, the tibial component of which consists of 2 parts: a highly conforming polyethylene insert freely rotating on a metal tray. Our case study relating to the implant of the first 110 knees operated on consecutively from 1991 to 1995 is reported, with an average follow-up of 6.3 years (range, 5-9 years). The average preoperative Knee Society Score was 78 points, and the average postoperative score was 156 points. The complications specifically related to the prosthetic components and which required revision surgery were 4: 2 cases of instability, 1 aseptic loosening of the tibial tray, and 1 traumatic dislocation of the tibial insert. A further 3 patients underwent reoperation for causes not strictly related to the implant: 2 because of intractable patellar pain and 1 because of periprosthetic ossifications that limited flexion. All of the complications were observed in patients operated on during the first 3 years of our experience, thus suggesting a definite learning curve with this prosthesis. No evidence of progressive radiographic periprosthetic osteolysis was recorded, and no relevant polyethylene wear was observed over time. Kaplan-Meier survival curves show the probability of survival to be 93.7% with revision surgery for any reason as an endpoint, and 96.3% with revision surgery for a mechanical reason as an endpoint. Certainty that mobile-bearing total knees are able to assure a longer life of the implant than the conventional models would require an evaluation of results over 15 to 20 years. However, in the meantime, these good preliminary results at least justify continuing the use of this type of prosthesis, which still awaits confirmation of the, as-yet-theoretical, advantage compared with fixed-bearing total knees.