LONG-TERM RESULTS AND SURVIVORSHIP ANALYSIS OF THE TOTAL CONDYLAR KNEE PROTHESIS

Introduction This study refers to the first 76 Total Condylar knee prostheses that were implanted in 66 patients, with a minimum follow-up of 10 years. Materials and methods There were 54 women and 12 men with an average age of 65 years (range 45-81). The diagnosis was osteoarthrosis in 63 knees and rheumatoid arthritis in 13. We were able to review 54 prostheses with an average follow-up of 13 years (10-17) using the rating system of the Hospital for Special Surgery and the Survivorship analysis. Results The results were excellent and good in 72,5 per cent knees and fair and poor in 22 per cent, 3 knees (5,5 per cent) had been revised for deep infection in 2 cases and for aseptic loosening in 1. Pain at rest was absent or mild in all but one patient; walking pain was absent in 32 knees (63 per cent), mild in 12 (23 per cent), moderate in 5 (10 per cent) and severe in 2 (4 per cent). Average range of motion was 89-degrees, ranging from 40-degrees to 120-degrees. A flexion contracture greater 5-degrees was seen in 8 knees (16 per cent). Instability in the frontal plane tested in full extension was more than 5-degrees in 10 patients (19.5 per cent). A significant deterioration of the results occurred in the last 4-5 years, since in 1988 excellent and good results were still 82 per cent. A loss of postoperative alignment of 5-degrees or more was observed in 11 knees: aseptic loosening was identified in 2 of these cases and deformation of the tibial component was seen in 1 knee. In the remaining 8 knees we observed increased lateral instability, compared to the postoperative evaluation. In this group of 8 knees we measured in the AP view the thickness of the tibial component on the lateral and medial side. We found polyethylene wear on the medial side in 4 cases. Ten of the 11 knees with loss of alignment had an early postoperative femoro-tibial axis less than 5-degrees. We observed radiolucent lines in 18 patellar and 27 tibial components. A width greater than 2 mm, correlated to an extension to 5 or more zones, was seen in 3 tibial components with aseptic loosening. Survivorship analysis using aseptic loosening, mechanical failure of the polyethylene and deep infections as end point gave a cumulative success rate at 10 years of 92 per cent% with 95 per cent confidence interval ranging from 85,1 to 98. Discussion Our study reports a lower percentage of excellent and good results if compared to other series of Total Condylar prosthesis with a comparable follow-up. A significant deterioration of the results occurred in the last years, but this was often not related to the knee itself but to poor general conditions in some patients. In this series there is a relevant number of knees with a post-operative alignment that today we dont' consider correct and all the aseptic loosenings occurred in knees with a tibial component positioned in varus. Conclusion Survivorship analysis gave a cumulative success rate comparable with those reported in other studies and confirmed the durability and longevity of this model of prosthesis.