This book addresses the background and significance of the factors potentially influencing the clinical and biological outcomes of metal-on-metal hip implants. Metal-on-metal bearings were introduced and evaluated as an alternative to other bearing couples, particularly metal-on-polyethylene, due to their enhanced wear resistance as determined in laboratory testing. Initially, reports of short-term clinical outcomes were favorable and an increasing number of metal-on-metal prostheses were implanted. Subsequently, isolated case findings describing adverse tissue responses around the articulation became the harbinger of an increasing number of reports describing pseudotumors and other significant lymphocytic-based responses associated with metal-on-metal prostheses. Questions have been raised as to whether this is an implant, design, or patient-specific response. The reasons why some patients have a negative biological response and pathology while others do not remain to be determined, but tens of thousands of patients in the US, the UK, and around the world are considered to be at risk. Leading researchers and clinicians describe the issues related to the nature of the biological and pathological responses and the protocols that should be followed to determine if an adverse response is occurring. This book is essential reading for researchers, engineers, and orthopaedic surgeons who are involved in the design, evaluation, and implantation of metal-on-metal prostheses.

The purpose of this study was to describe actual usage patterns for metal-on-metal (MOM) bearings in the United States using a nationally representative database. The 2005-2009 nationwide inpatient sample (NIS), in combination with the 2009-2010 state inpatient databases (SIDs), was employed to identify primary total hip arthroplasty (THA), revision THA, and resurfacing hip arthroplasty (RHA) patients implanted with a MOM bearing using ICD-9-CM codes. The MOM patient population was characterized by gender, age, race, U.S. Census region, hospital characteristics, and insurance coverage. The prevalence of MOM bearing usage was estimated between 2000 and 2010. Between 2005 and 2010, MOM bearing usage in the United States ranged between from 32 % and 40 % of primary THAs and from 26 % and 32 % of revision THAs. Utilization of MOM bearing types in primary/revision THA and RHA peaked in 2008. By 2010, 755 000 patients were estimated to be implanted with MOM bearings in the United States between 2000 and 2010, we estimated that 83.7 % of MOM bearings in the United States were implanted during primary THA procedures, 11.7 % during revision THA, and the remaining 4.6 % during RHA. Our research demonstrates that the prevalence of MOM increased substantially up to a high water mark in 2008. Despite uncertain indications for use, MOM bearings were used extensively in female and elderly patients.

To determine what the trends for the use of total hip arthroplasty bearings have been in the United States and how the Food and Drug Administration (FDA) warning on the use of metal on metal bearings have affected surgeon's decisions concerning their use, a survey was performed on the fellows of the American Academy of Orthopaedic Surgeons (AAOS). Two thousand randomly selected practicing fellows were invited to take part in the AAOS 2010 survey. Of those invited, 170 (8.5 % response rate) completed the survey. Confidence interval (CI) values at 95 % were provided for each survey item. There were no significant differences between invitees and respondents in terms of practice setting and gender. The majority of respondents (79.2 %) match their patients' function/activity to the bearing surface used in total hip arthroplasty (THA). Respondents mostly use peer reviewed publications (92.9 %), and personal experience (81.7 %) when making a decision on bearing use in THA. Almost 80 % of the respondents indicated that their hospitals do not limit their choice of implants. Cross-linked polyethylene has been the most used type of bearing surface before 2010 (74.80 %) and currently (78.62 %). Metal-on-metal and ceramic-on-ceramic use decreased; however, there are no significant differences between the uses of all types of bearings before 2010 and currently. Given the current debated issues, 75.6 % of respondents are less likely to use metal-on-metal bearing in the future; 22 % are not affected. The majority of respondents (70.3 %) indicated that ceramic-on-ceramic bearing have fewer wear particles. More than half (56.7 %) indicated that metal-on-metal (MoM) has the longest survivorship. This survey indicated that surgeons responded that their use of MoM bearings will likely decrease in the future but the numbers in this survey show no significant difference in their use before and after the FDA warning for MoM bearings. The survey does show that most surgeons believe that they will have less choice as directed by their hospital or insurance companies in their bearing use in the near future due to health economics and the efforts to decrease cost. Only time will tell if surgeons who indicate the use of MoM will decrease over time actually comes to fruition or if the use of MoM will continue at its current rate. This survey indicates that although the trend shows a decrease in their use, it was not statistically significant.

Few subjects related to the design or construction of machinery are of greater importance than the subject of bearings. All classes of mechanisms have bearings of some kind and bearings that are properly designed and constructed are a necessity. As every experienced mechanic knows, a poor bearing may tie up a machine or even cause an entire plant to shut down temporarily. Owing to the importance of this subject, designers and mechanics in general should understand the fundamental principles governing bearing design and should know what approved types are in common use on different classes of machinery. This treatise deals exclusively with plain bearings, ball and roller bearings being covered in another book of this series. The types of plain bearings illustrated in a connection with the following chapters were selected to show how designs are modified to suit different conditions, and also practical methods of arranging bearings to insure adequate lubrication and thorough protection against the entrance of any foreign material liable to injure the bearing surfaces. The designs illustrated were taken from actual practice and have proved satisfactory when properly constructed and applied. This treatise contains, in addition to the features mentioned, condensed information on corn- positions of various bearing metals, their properties, the classes of service to which different bearing alloys are adapted, and the general methods of procedure in designing plain bearings to meet different service conditions.