Are unconstrained components essential in total knee arthroplasty? Long-term results of the Blauth knee prosthesis

For 17 years, the Blauth total knee prosthesis has been implanted with its basic constructional features remaining unchanged. While it is true that the prosthetic components are constrained by a mechanical hinge, load transmission is actually effected in accordance with the low-friction principle through the cup-shaped condylar surfaces. Packing of the prosthesis in the bone is ensured by large load-bearing surfaces and by specific elements intended for rotational stability. In a comprehensive follow-up review, 497 implants were studied over a period of one to 15 years (average, 45 months). Aseptic loosening occurred in only 1.2% of the prostheses, and deep infection was found in 3% of the patients in the follow-up review. According to survival statistics, the probability of finding prostheses without deep infection or loosening after more than ten years is 89%. The efficiency of total knee arthroplasty (TKA) by hinged prostheses should therefore not be judged by the results obtained with the pioneer implants, which date back to the beginnings of TKA. The clinical results obtained clearly demonstrate that there is 90 degrees knee flexion in more than 88% of the implants. A subjective appraisal demonstrated substantially less pain compared with the preoperative findings. Problems originating from the patella were recorded in less than 10%. However, in 1985, an improved prosthetic design was introduced that also provided for the replacement of the posterior surface of the patella and for a proximally extended patellar bearing. The position of the hinge and implant packing remained unchanged. The results obtained so far with the modified prosthetic design are very good.