Abstract
Total knee replacements (TKRs) are being more commonly performed in active younger and obese patients. Fifteen year survivorship studies demonstrate that cemented total knee replacements have excellent survivorship, with reports of 85% to 97%. However, inferior survivorship occurs in younger patients and obese patients who would be expected to place increased stress on the bone cement interfaces. Cementless fixation for total knee replacement has not gained widespread utilization due to the plethora of poor results reported in early series. These poor results do not reflect that cementless fixation is not obtainable, since an almost universal acceptance of cementless fixation for total hip replacement has shown. A Cochrane database study of total knees with roentgen stereophotogrammetric analysis (RSA) demonstrated that the risk of future aseptic loosening should be 50% less with cementless fixation. The poor initial results with cementless total knee replacement have occurred due to poor implant designs such as cobalt chrome porous interfaces, poor initial tibial component fixation, lack of continuous porous coating, poor polyethylene, and use of metal-backed patellae.
I have used cementless fixation for total knee replacements for young, active, and heavy patients since 1986 when durability over 20 years is desirable. My series of over 1,000 cementless TKRs represents about 20% of the total knees I have performed from 1986 to 2015. I have seen failures in my series due to the initial use of metal-backed patellae with thin polyethylene and use of screws and femoral and tibial components which provide access to the metaphyseal bone for polyethylene wear debris. Overall failures were still significantly low due to the use of highly porous titanium surfaces on the tibial and femoral components. Isolated aseptic loosening only occurred on one tibial component in my entire series. With the advent of utilizing implants with continuous porous surfaces and highly cross-linked polyethylene, and elimination of use of metal-backed patellae and tibial screws, I have only had one revision due to aseptic loosening or osteolysis in the last 760 cases performed since 2002.
Almost 50% of total knees are now performed on patients under the age of 65. A 55-year-old patient has a 30-year life expectancy. Modern total knee replacement design has made biological fixation predictable for young and heavy patients. Because it is a biological interface, it should respond better than cement to the increased stresses that will be applied over many years by our younger, more active and heavier total knee population.
