Ceramics for Prosthetic Hip and Knee Joint Replacement Mohamed N. Rahaman* ,w and Aihua Yao Department of Materials Science and Engineering, University of Missouri-Rolla, Rolla, Missouri 65409 B. Sonny Bal Department of Orthopaedic Surgery, School of Medicine, University of Missouri-Columbia, Columbia, Missouri 65212 Jonathan P. Garino Department of Orthopaedics, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104 Michael D. Ries Department of Orthopaedic Surgery, University of California, San Francisco, California 94143 The most commonly used bearing couple in prosthetic hip or knee joint replacements consists of a cobalt–chrome (CoCr) metal alloy articulating against ultrahigh-molecular-weight polyethylene. Ceramics have been used as an alternative to met- al-on-polyethylene in joint replacement surgery of arthritic hips and knees since the 1970s. In prosthetic hip and knee bearings, ceramic surfaces offer a major benefit of drastically reduced wear rates and excellent long-term biocompatibility, which can increase the longevity of prosthetic hip and knee joints. This benefit is important clinically because hip and knee replacement has become a very common surgical procedure, particularly in the United States, and because these procedures are being in- creasingly performed in younger patients who place greater de- mands on the prosthetic bearings. However, ceramics are brittle and the risk of catastrophic bearing failure in vivo, while rare, is a major concern. Improvements in material quality, manufac- turing methods, and implant design have resulted in a drastic reduction of the incidence of such failures, so that modern ce- ramic bearings are safe and reliable if used with components of proven design and durability. Future material improvements are actively being investigated to reduce the risk of ceramic-bearing failures even further. The purpose of this article is to review the structure, properties, applications, and limitations of the ceram- ics that have been used in orthopedic bearings, and to describe the new ceramic composite materials and surface treatments that will be available for joint replacement surgery in the near future. I. Introduction T HE hip prosthesis has been the most active area of joint re- placement research and development for decades. Ar- throplasty devices for the hip joint have been under development since the early 1900s. A major advance in the ef- ficacy of the hip implant was made around 1960 by Sir John Charnley, 1 who introduced a total hip arthroplasty (THA) de- vice consisting of a metal femoral prosthesis bonded to bone with poly(methyl methacrylate), PMMA, and an acetabular component made of ultra-high-molecular-weight polyethylene, UHMWPE, also cemented to bone with PMMA. This system has seen a number of variations over the years, but the basic design still applies to all modern prostheses for THA. With the success of the hip prosthesis, similar material configurations have been used with the appropriate geometrical design for total knee arthroplasty (TKA). The standard bearing coupling in THA and TKA today con- sists of a metal, typically a cobalt–chromium (CoCr) alloy, ar- ticulating against UHMWPE (Figs. 1 and 2). Approximately 500 000 total hip and knee joint replacements are being per- formed annually in the United States and Europe, 2 and this number is expected to increase rapidly as the population ages and as these procedures are increasingly demanded by younger patients who wish to remain active despite arthritic degeneration of their joints. The average lifetime of prosthetic devices with CoCr–UHMWPE bearings is 10–15 years. Approximately 25% of the total hip and knee joint replacements are actually repeat surgeries due to premature failure of the prosthetic joints by aseptic loosening. 3 The product of bearing wear, microscopic particulate debris in the joint space, leads to periprosthetic in- flammation and implant loosening. Ceramics have been used as an alternative to the CoCr– UHMWPE-bearing couple in both THA 4–6 and TKA 7–9 for several decades (Figs. 1 and 2). Alumina (Al 2 O 3 ) was introduced as a candidate material for orthopedic bearings in the 1970s, and Feature D. Green—contributing editor *Member, American Ceramic Society. w Author to whom correspondence should be addressed. e-mail: rahaman@umr.edu Manuscript No. 22642. Received January 1, 2007; approved March 26, 2007. J ournal J. Am. Ceram. Soc., 90 [7] 1965–1988 (2007) DOI: 10.1111/j.1551-2916.2007.01725.x r 2007 The American Ceramic Society