Unsere Kniegelenkprothesen mit Patellaersatz*)

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Abstract
In the 13 years since the first Blauth total knee joint replacement was implanted, in August 1972, it has proved highly successful. This is borne out by the result of a prospective long-term study. Out of 488 patients who had been provided with such a prosthesis up to the beginning of 1984, 398, or 82%, were included in the study. Sixty patients had meanwhile died, and 24 could not be contacted. Six prostheses had to be removed. The follow-up quota of the surviving patients corresponded to 94%. The mean duration of observation was 40 months, with a minimum of 12 and a maximum of 144 months. Of the patients, 35% suffered from rheumatoid polyarthritis, and 61% from gonarthrosis. The mean postoperative flexion and extension values were 98-3-0.degree.. About 10% of the patients still claimed to suffer appreciable pain when starting to move and when bearing weight, as compared to approx. 95% preoperatively. Severe complications were 9 deep infections (2.3%) and 5 cases of aseptic loosenings (1.3%). There were no stress fractures or breakages of the prosthesis material in the patients follow up. A retropatellar pain syndrome was found in 8.3% of the patients, i.e., definite pain when standing up, on stairs, or when starting to move. For this reason the original design of the prosthesis was developed further and complemented, inter alia, by an artificial patella. The principal modifications are as follows: The femoral section was given a concave shape in the sliding bearing of the kneecap and elongated proximally. The lateral condyle shell was made slightly too high in order to prevent lateralizations of the patella. We shaped the artificial patellar joint surface as a spherical section and adapted it to the femoral sliding groove. The valgus angle of the femoral prosthesis shaft was reduced from 8.degree. to 6.degree.. We reduced the overall length of the prosthesis by 4 cm. Additionally, the supporting surfaces for the femoral and tibial parts of the prostheses were enlarged and the range of movement of the prosthesis was increased. Finally we designed three different sizes of prosthesis to suit the range of variation in human knee joints better. The difference between each size is 15%. A number of auxiliary instruments are available to facilitate accurate implantation. Without exception, our experience so far with the modified prosthesis models has been good. The first prosthesis of this kind, with replacement patella, was implanted in February 1983.

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