WPC 2 ZB x6X@X@2#|x CONGRESSIONAL TESTIMONY B.N.Stulberg, M.D. $ $ Chairman, Committee on Biomedical Engineering ` ` ` American Academy of Orthopaedic Surgeons  I am pleased to say a few words to you on behalf of the American Academy of Orthopaedic Surgery. Our specialty deals with medical care of the musculoskeletal system, and as such has more than a 40 year history of using implantable medical devices. Our field has been characterized by intense basic and clinical research into the performance of such devices, and has been able to substantially improve the quality of life of our patients because of these devices. I believe that we can offer a perspective to this recent concern relating to the availability of basic materials for the manufacture of devices that will be used for biological implantation, and I hope that it might prove of benefit in your deliberations. There are three basic messages from this perspective:  1) Any implantable device that is subjected to stress has ` ` ` the potential to fail over time. This is particularly ` ` ` true for devices used in load bearing applications; 2) The failure patterns of devices used in load bearing ` ` ` capacity is usually multifactorial, involving   varying contributions from device related factors,    technical factors of implantation, and biological pppfactors, including patient usage; and 3) The risk to our patients, our specialty, and to the ` ` ` American manufacturers of the products we use is   substantial if we equate device failure with    xxxinadequacies of the base materials incorporated into    these devices. Until such time as new mechanisms for pppdevice evaluation prior to and after implantation are pppdeveloped and applied routinely, statutory protection pppwill be necessary to protect suppliers of base materials. These new mechanisms will require the hhhcombined efforts of scientists, manufacturers, hhhregulatory agencies and clinicians to establish hhhpppprocesses of evaluation that limit the exposure of patients to what ultimately become poorly performing implants. Page 2 In short, this perspective will suggest that there is no material implanted in a patient that could not fail eventually. These failures are not necessarily the result of material problems, but are intricately related to the design of the part in which the material was used, the way that the device was implanted in the patient, the manner in which the patients system has adapted to the device, and the level of use to which that device is subjected. To lay blame to the material alone underestimates the problem substantially. While the basic biomaterials pulled off the market by DuPont and Dow Corning have only a small impact on the orthopaedic marketplace today, we do have a number of materials used for a variety of applications that could be placed in similar jeopardy if the suppliers of these materials chose to withdraw from the medical marketplace. The most obvious of these materials is the polyethylene component of total joint replacement prostheses.H!H!H! Approximately 450,000 patients per year undergo hip or knee replacement surgery in the United States each year. Each of these devices has a component that is fabricated from a high strength metal, which mates with a surface of ultrahigh molecular weight polyethylene (UHMWPE "polyethylene"). I would like to use the application of materials in devices used for total hip replacement surgery as an example of our triumphs and failures, and the impact of the basic materials. This surgery is used to treat endstage arthritis of the hip joint, fractures of the upper part of the femur, problems related to blood flow abnormalities of the hip, tumors involving the hip joint, and a host of other applications. It provides predictable pain relief and substantial improvement in function of the joint and of the patient, and allows the restoration of a patient's quality of life. This operation is performed over 250,000 times per year in the United States, and when combined with other joint replacement procedures, has spawned a $10 Billion industry. The operation first came to this country in 1968. The hip joint carries forces of approximately 3 to 5 times body weight with each step that an individual takes. The average individual walks on his (her) hip approximately 1 million times per year. Thus it is easy to see that devices used to replace this joint are to be subjected to substantial forces over time. While in the early years of joint replacement surgery we experienced some breakage of devices, a number of other mechanisms of device failure have been identified. A large majority of these mechanisms of failure are determined from careful analysis of the concepts used to design the implant, the processes involved in manufacturing the device, the clinical enviroment and clinical performance of the device when it was implanted, and a careful Page 3 analysis of the retrieved implant once it is removed, either for failure or in post mortem examination. This entire process has been called the "life cycle" of the implant, and is only recently receiving careful attention from clinicians and scientists. There may be three broad categories that can be used to describe device failure. These are: 1) factors related to the device itself, which include its design and the materials of which it is made; 2) factors related to the patient in whom it is implanted; and 3) factors related to the implantation of the device.  Currently of significant concern to the orthopaedic community is the issue of wear of the UHMWPE. When hip replacement surgery first came to the United States in 1968, the devices used were of stainless steel stems mated with socket devices of all polyethylene. These were anchored with bone cement. With time, we found that certain stems devices were not strong enough, and new metal alloys and processes for manufacturing were devised; we found that cement could fragment and cause debris leading to excessive bone loss; and we saw wearing of the polyethylene. We moved to newer devices, requiring substantially greater sophistication in manufacturing, that would address these problems. New processes providing alternatives to the use of cement, required mechanisms to attach devices directly to bone, required improved metallurgical processes, and led to newer approaches to using polyethylene. These approaches have resulted in markedly improved devices that have found usage in an expanding number of circumstances, many of which place even greater stresses on devices than have been previously felt to be reasonable most notable is that in a famous baseball player. Polyethylene is still an extremely important component of each of these devices. Our attempt to move to new approaches for bone attachment appears to have had a negative impact on the performance of this polyethylene. In one series of patients, we have been seeing evidence of wear of a particular device in as many as 50 % of patients by 7 years a rate of wear that is nearly twice as fast as what we were previously experiencing. Specific features of this wear were the thickness of the polyethylene used in the device, the size of the patient, the activity level of the patient, and the angle of implantation of the device. To blame this failure rate on the base material, and to hold the suppliers accountable, would not be accurate nor would it be in the best interest of our industry. At present, the supply of polyethylene is from two sources. The percentage of polyethylene that these manufacturers produce that goes to the medical marketplace represents approximately 1/2 of 1 percent (0.5%) of its total output. If for liability reasons, these manufacturers were to withdraw from the medical marketplace, Page 4 we would be forced to return to approaches used before 1968. This would have the impact of undermining the 10 billion dollar industry associated with joint replacement activity, driving most of the industry offshore or making us entirely dependent upon manufacturers outside of the United States.  A good deal of research effort, in time and money, by academic centers, orthopaedic manufacturers, and materials scientists have been focused upon understanding the mechanisms of polyethylene wear, the consequences of wear, and the design issues of the devices that can decrease the likelihood of wear. All efforts at research are directed at improving the performance of the material. Only recently are scientists and manufacturers looking for alternative materials, an expensive process that could take years to develop and bring to the marketplace. The point which we wish to make is that none of the materials we use is perfect. As we identify problems in certain applications of these materials and address them directly, we run the risk of compromising performance of other aspects of the devices. There is likely to be either a biological or biomechanical consequence (or both) to each material we use in a biological environment. It is clear that there are factors relating to device failure that physicians may not be able to completely control the biological factors such as infection, or rejection. But there also are factors that clearly can be controlled by the physician such as the implantation of appropriate components in the proper position; and by the manufacturer, such as the quality of the material selected and the proper shaping and characterization of the materials as they are fashioned into devices. Each of these areas has an impact on how that material will perform once it is implanted. We believe it is important identify those areas of the medical community that have this precarious relationship of high risk with low return, and to provide them with statutory protection. It will be similarly important to work toward newer methods to predict and insure safety of devices over extended periods of implantation, and to provide a cooperative regulatory enviroment that stimulates their development. Thank you.