Acrylic bone cements: influence of time and environment on physical properties.

Acrylic bone cements are in extensive use in joint replacement surgery. They are weight bearing and load transferring in the bone-cement-prosthesis complex and therefore, inter alia, their mechanical properties are deemed to be crucial for the overall outcome. In spite of adequate preclinical test results according to the current specifications (ISO, ASTM), cements with inferior clinical results have appeared on the market. The aim of this study was to investigate whether it is possible to predict the long term clinical performance of acrylic bone cement on the basis of mechanical in vitro testing. We performed in vitro quasistatic testing of cement after aging in different media and at different temperatures for up to 5 years. Dynamic creep testing and testing of retrieved cement were also performed. Testing under dry conditions, as required in current standards, always gave higher values for mechanical properties than did storage and testing under more physiological conditions. We could demonstrate a continuous increase in mechanical properties when testing in air, while testing in water resulted in a slight decrease in mechanical properties after 1 week and then levelled out. Palacos bone cement showed a higher creep than CMW3G and the retrieved Boneloc specimens showed a higher creep than retrieved Palacos. The strength of a bone cement develops more slowly than the apparent high initial setting rate indicates and there are changes in mechanical properties over a period of five years. The effect of water absorption is important for the physical properties but the mechanical changes caused by physical aging are still present after immersion in water. The established standards are in need of more clinically relevant test methods and their associated requirements need better definition. We recommend that testing of bone cements should be performed after extended aging under simulated physiological conditions. Simple quasistatic and dynamic creep tests seem unable to predict clinical performance of acrylic bone cements when the products under test are chemically very similar. However, such testing might be clinically relevant if the cements exhibit substantial differences.

The genesis and evolution of acrylic bone cement.

In 1957 John Chamley and I began to discuss the question of cement fixation of femoral prostheses. This was an independent development, because we had no knowledge of any other work in this area. Our conclusion was to grout in the prosthesis with a suitable cement. I selected a cold-curing acrylic denture repair material called Nu-Life as most appropriate. This material proved satisfactory in laboratory and clinical trials, and in 1958 Chamley undertook hip replacement using a cemented femoral prosthesis in six patients. This clinical success aroused great interest and some skepticism, because it was not always appreciated that Charnley and I had a substantial body of scientific data that justified this new approach to arthroplasty. Not surprisingly,the clinical aspects received most emphasis in the next decade. The scientific data were published mostly in the dental literature and were forgotten by the time cementation arthroplasty was generally accepted and so were rediscovered in subsequent years.

Clinical development and current status: Europe.

This article reviews the development and current status of cemented fixation in total hip replacement in Europe. Key points include the wide country-to-country variation in use of cemented vs. non-cemented fixation and the largely overlooked importance of the choice of bone cement as a factor highly correlated with clinical outcome. Laboratory studies by the authors are also reviewed. Results suggest that the type of acrylic bone cement used affects wear phenomena at the implant/cement interface. Further studies by microcalorimetry suggest that certain aspects of acrylic starting materials (low molecular weight and use of radiation sterilization) affect long-term physico-chemical stability and may thus influence clinical outcomes.

Acrylic bone cement: clinical development and current status in North America.

This article discusses issues surrounding acrylic bone cement and covers functional results, mechanism and definition of failure, design issues, wear and alternate bearing surfaces, revision, and evolution of concepts regarding infection, dislocation, thromboembolic issues, surgical approach, bone loss and bone grafts, and finally a couple of problems the author sees for the future.

The science of bone cement: a historical review.

The use of PMMA bone cement has been a key factor in the advent of joint replacement as a surgical option. Despite revolutionary changes in joint replacement technology for the treatment of hip and knee arthritis, the use of PMMA bone cement in its intraoperative application has not significantly changed since Harris' description of third generation cement technique. Future answers to questions regarding cemented implant longevity may lie in the further improvement of existing PMMA technology and standardization of the manufacturing of PMMA bone cement intraoperatively.

Evaluation of an unused 1952 Ridley intraocular lens.

PURPOSE: To evaluate an unused 1952 historic Ridley intraocular lens (IOL) brought to Bombay, India, in 1952 from an Oxford Ophthalmologic Conference in England and given to 1 of the authors during his residency. SETTING: Alcon Laboratories, Fort Worth, Texas, USA. METHODS: The Ridley IOL was evaluated at Alcon Laboratories, Inc., using the established procedures of its Intraocular R&D Laboratories. Various optical and physical aspects of the Ridley lens were evaluated including (1) dimensions, (2) weight, (3) power, (4) resolution efficiency and modulation transfer function (MTF), (5) surface sphericity by interferometry, (6) ultraviolet (UV)-visible transmission characteristic, (7) attenuated total reflectance (ATR)-Fourier transform infrared reflectance spectrum, and (8) cosmetics by visual inspection using light microscopy. RESULTS: This 8.5 mm diameter, 2.4 mm thick, 23 diopter biconvex IOL weighed 108 mg. The ATR spectrum, UV-visible transmission, and refractive index confirmed its poly-(methyl methacrylate) material. The 0.56 MTF value at 100 line pairs/mm, per the International Standards Organization--IOL Optics Standard, and 93% resolution efficiency in water, per the American National Standard Institute IOL Optics Standard, revealed the IOL's excellent optics. This was confirmed by 0.278 wave root mean square surface figure as measured by Zygo interferometer using a 633 nm wavelength. Visual inspection revealed rough edges with sharp corners and some surface scratches. Early clinical experience with Ridley IOLs in Bombay, India, is briefly given. CONCLUSION: The Ridley IOL had excellent optical quality, meeting the requirements of current IOL optics standards. The selection of its dimensions was guided by the human crystalline lens, and the Ridley IOL was half as bulky. Although its clinical results were mixed, successful cases inspired subsequent improvements, leading to modern, highly satisfactory IOLs. This IOL represented a revolutionary innovation in ophthalmology.