Comparing the results of different types of knee replacement. A method proposed and applied.

Many knee replacement prostheses, embodying various principles of design, are now available and there is need for a method by which valid comparisons of results can be made. An important criterion of success is durability, so the length of time the prostheses have been in situ must be taken into account. Such a method is proposed here and is applied to the results of 673 knee replacements, of nine different types, implanted at the same hospital between 1970 and 1983. A prosthesis was considered to have failed if it had been removed or persistently caused severe pain. Two types of prosthesis were found to be significantly less successful than the other seven, between which none consistently showed significant superiority. Results for the seven types were similar despite the facts that they had been used for knees with different degrees of damage, some as secondary implants, and that they were of different design and at different stages of technical development. The more recently introduced types of prosthesis, designed to have theoretical advantages, were found in practice to be no more successful than the models they superseded.