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© 1998 The Journal of Bone and Joint Surgery, Inc. Health-Related Quality of Life after Knee Replacement. Results of the Knee Replacement Patient Outcomes Research Team Study*   , TORONTO, TORONTO, INDIANAPOLIS, TORONTO, ONTARIO, CANADAInvestigation performed at the Departments of Medicine, Surgery, Statistics, and Health Administration, University of Toronto, Toronto; Institute for Policy Analysis, Toronto; the Departments of Medicine, Regenstrief Institute for Health Care, Bowen Research Centre, and School of Public and Environmental Affairs, Indiana University, Indianapolis; and Research Triangle Institute and Glaxo Wellcome, Research Triangle Park
A cross-sectional, community-based survey of a random sample of 1750 of 242,311 Medicare recipients was performed. The patients were at least sixty-five years old and had had a primary or revision knee replacement (either unilaterally or bilaterally) between 1985 and 1989. Three samples were surveyed separately: a national sample (to reflect the United States as a whole) and samples from Indiana and the western part of Pennsylvania (sites chosen for convenience to assess the validity of the findings for the national sample on a regional level). Each sample was stratified by race, age, residence (urban or rural), and the year of the procedure. Valid and reliable questionnaires were used to elicit the participants' assessments of pain, physical function, and satisfaction two to seven years after the knee replacement. Of the 1486 patients who were eligible for inclusion in the survey, 1193 (80.3 per cent) responded. The mean age of the respondents was 72.6 years. Eight hundred and forty-nine respondents (71.2 per cent) were white, and 849 (71.2 per cent) were women. The participants reported that they had little or no pain in the knee at the time of the survey, regardless of the age at the time of the knee replacement, the body-mass index, or the length of time since the knee replacement. After adjustment for potential confounding variables, predictors of better physical function after the replacement were an absence of problems with the contralateral knee, primary knee replacement (rather than revision) (Indiana sample only), and a lower body-mass index (Indiana and western Pennsylvania samples). Four hundred and fifteen (85.2 per cent) of the 487 patients in the national sample were satisfied with the result of the knee replacement. In what we believe to be the first community-based study of the outcome of knee replacement, patients reported having significant (p = 0.0001) and persistent relief of pain, improved physical function, and satisfaction with the result two to seven years postoperatively. The findings of the present study suggest that age and obesity do not have a negative impact on patient-relevant outcomes (pain and physical function). Dissemination of these findings has the potential to increase appropriate referrals for knee replacement and thereby reduce the pain and functional disability due to osteoarthrosis of the knee.
The use of knee replacement has increased exponentially over the past decade. As is the case for many other operative procedures, the rate of knee replacement has been shown to vary among geographic areas, even after adjustment for geographic differences in the prevalence and severity of osteoarthrosis of the knee7,22,39. This variation raises concerns regarding the access of patients to knee replacement and the appropriateness of care. Potential explanations for such variation include differences of opinion among patients, referring physicians, and orthopaedic surgeons about the indications for and the effectiveness of knee replacement; variations in the supply of health-care professionals; and geographic as well as cultural differences in patients' propensities to seek a knee replacement27,28. The assumption has been that the procedure is overutilized in areas where the rate is high. Policymakers have generally assumed that the so-called best rate is similar to the mean rate. However, the best rate may be closer to the high rates in areas where the need for the procedure is high. Knee replacements are performed primarily in the elderly, and most of the knee replacements done in the United States between 1985 and 1990 for individuals who were sixty-five years old or more were performed because of osteoarthrosis9. This finding is not surprising, as osteoarthrosis is one of the most prevalent chronic and disabling diseases in adults, affecting two-thirds of those who are sixty-five years old or more10,11,14,16,26,29. Furthermore, as the population ages, the prevalence of osteoarthrosis is expected to increase1. Osteoarthrosis of the knee results in pain, loss of function, and a reduced quality of life12,24,38,40. Joint replacement is the accepted treatment for patients with advanced osteoarthrosis of the knee (and hip) who, despite appropriate medical management, have an unacceptable level of pain or physical function, or both6,17,18,37. However, there is a documented lack of consensus among orthopaedic surgeons and referring physicians regarding the indications for and the outcome of knee replacement8. As a result, patients who may benefit from knee replacement may not be offered or may not consider this treatment. Although the findings of previous studies have suggested that knee replacement is effective for the treatment of advanced osteoarthrosis of the knee, many of these studies have focused on improvements in joint mechanics (such as range of motion and stability) and in rates of postoperative complications and subsequent revision4,5 rather than on relief of pain and improvement in physical function. Furthermore, those studies generally have reflected the experience of patients who were managed in tertiary-care centers by surgeons who performed a high volume of replacements; this tendency may limit the generalizability of the results. Because approximately 84 per cent of the knee replacements performed in the United States are done at non-teaching hospitals9, it is essential to conduct studies in which the results of knee replacements performed in this setting are evaluated from the perspective of the patient. This information is necessary so that clinical guidelines can be developed for the determination of who should have a knee replacement and so that patients and their physicians can make informed decisions about whether a knee replacement should be considered. The purpose of the present study was to identify the determinants of optimum patient-relevant outcomes in a representative sample of patients who had had a knee replacement. Measures of effectiveness included patients' assessments of pain in the knee, physical function, and satisfaction with the long-term result. The current report represents the findings of the Knee Replacement Patient Outcomes Research Team, which is funded by the Agency for Health Care Policy and Research to gather information on large, unselected national samples of health-care recipients regarding the results of knee replacement.
Medicare Provider Analysis and Review files were used to identify all hospitalizations for knee replacement in the United States from January 1, 1985, through December 31, 1989. (Procedures performed before October 1, 1989, had a code of 81.41 according to the International Classification of Diseases, Ninth Clinical Modification [ICD-9-CM], and the procedures performed on or after October 1, 1989, had a code of 81.54 [knee replacement] or 81.55 [revision knee replacement].) Of the 317,364 records, 51,413 (16.2 per cent) were excluded because the patient was known to have died; 18,725 (5.9 per cent), because the patient was less than sixty-five years old; 4126 (1.3 per cent), because the patient was enrolled in a health maintenance organization and there was concern regarding incomplete data and difficulty in following such a patient over time; 377 (0.1 per cent), because the patient may not have had the procedure (the ICD-9-CM code indicated that the procedure had been miscoded or had not been performed [for example, V64.1], or the total charges were less than $5000 [in 1989 dollars] and the length of stay was shorter than four days); 317 (0.1 per cent), because the patient was eligible for Medicare under the End Stage Renal Disease program; and ninety-five (0.03 per cent), because the patient was not a resident of the United States. Three stratified samples were chosen from the remaining 242,311 patients: one sample from Indiana, one from the western part of Pennsylvania, and one from the United States as a whole (to serve as a national sample). The samples from the state of Indiana and the western part of Pennsylvania were chosen for convenience and were used to assess the validity of the findings for the national sample on a regional level. The national sample was selected to be representative of the United States population of Medicare recipients. Six sampling strata were defined on the basis of the factors that we were most interested in examining: age, race, and geographic area of residence. The strata included (1) white patients who were less than eighty years old and lived in rural counties, (2) white patients who were eighty years old or more and lived in rural counties, (3) white patients who were less than eighty years old and lived in urban counties, (4) white patients who were eighty years old or more and lived in urban counties, (5) all black patients, and (6) all patients who were of another race or for whom the race was unknown. In order to ensure that there was a sufficient number of patients in each stratum to study the effect of these factors on the outcome of knee replacement, the sizes of the strata were set to equalize the variances in the strata means20. The sizes of the samples for each of the five years of the study were approximately equal. The surveys of the three samples were conducted separately. An initial lead letter from the Health Care Financing Administration was mailed, in February 1992, to a total of 1750 patients who had had a knee replacement (including 750 patients in the national sample, 500 in the Indiana sample, and 500 in the western Pennsylvania sample). A questionnaire then was mailed in March 1992, and another was mailed, six weeks later, to any patient who had not responded. Patients who did not respond to either questionnaire were contacted by telephone to verify their address; to explain the importance of the study, the voluntary nature of participation, and the confidentiality of all data obtained; and to encourage completion of the mailed questionnaire. Patients who had returned completed questionnaires were contacted by telephone if there were any missing or uninterpretable responses to predetermined critical questions. Participants received no remuneration for completion of the questionnaire. Informed consent for participation in the survey was assumed, as is standard for all mail surveys, by the respondent's completion and return of the questionnaire. The self-administered questionnaire was designed to obtain demographic information and to elicit the patients' assessments of general-health status, pain in the knee, and physical function at the time of the survey and, on the basis of their recall, during the four weeks before the knee replacement. Demographic information included age (sixty-five to sixty-nine years old, seventy to seventy-four years old, seventy-five to seventy-nine years old, eighty to eighty-four years old, or eighty-five years old or more), gender, education, race, income, and living circumstances. The participants were asked to describe their occupation within the week before they received the questionnaire and within the four weeks before the knee replacement. They were instructed to indicate all of the response options that applied, which included working for pay or on a volunteer basis, working as a full-time homemaker, retired, unemployed or laid off, and disabled or unable to work. The height and weight at the time of the replacement and at the time of the survey were requested so that the body-mass index could be calculated. The participants also were asked to give their reasons for having the knee replacement and to indicate whether the operation was unilateral or bilateral, whether it was a primary or revision procedure, whether a previous or subsequent operation (such as an osteotomy or another procedure) had been done on the involved knee, whether there were problems with the contralateral knee (and if so, whether they were mild, moderate, or severe), and whether there were medical problems that limited daily activities. Information also was obtained regarding the use of medications for pain or swelling in the involved knee during the four weeks before the knee replacement as well as at the time of the survey. The self-administered Short Form-36 (SF-36)34 was used to assess the general-health status of the patient at the time of the survey so that the outcome of the knee replacement could be interpreted in the context of overall health. Comorbidity was measured in terms of the number of patient-reported, physician-confirmed medical diagnoses. We were particularly interested in specific comorbidities that might be expected to have an impact on the outcome of knee replacement (such as peripheral vascular disease) or on the function of the lower extremity (such as amputation or stroke). Pain in the knee and physical function were measured with use of the self-administered Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), a reliable and valid instrument that was initially developed for use in outcome studies of osteoarthrosis of the hip and knee2,3, and with use of a modification of the clinical rating system of the Knee Society, an unvalidated instrument that has been widely used by orthopaedic surgeons19. The WOMAC consists of three domains: physical function (seventeen items), pain (five items), and stiffness (two items). The total score is obtained by aggregating the domain scores. We used a modified version of the Knee Society scale because the physical examination component of the score could not be obtained with use of a self-administered questionnaire. Thus, the total score was derived from the scores for pain (one item), walking ability (one item), the ability to use stairs (one item), and the use of assistive devices (one item). Patients also were asked to rate the involved knee on a 5-point scale from much better to much worse than before the knee replacement and to rate their overall satisfaction with the knee replacement on a 5-point Likert-type scale from very satisfied to very dissatisfied. The primary diagnosis was obtained from the Medicare diagnosis fields (derived from hospital records) and was categorized as non-traumatic osteoarthrosis, rheumatoid arthritis, traumatic osteoarthrosis, or "other," according to the coding system of the ICD-9-CM. Patients who had had bilateral knee replacement during the same hospitalization were asked to report on the right knee. The questionnaire was reviewed by an advisory panel of orthopaedic surgeons, rheumatologists, general internists, family physicians, biostatisticians, psychometricians, and health-services researchers to ensure face and content validity, and it was pretested in a group of fifty-five elderly patients at three sites to determine patient acceptability and ease of administration. The questionnaire took forty-five to sixty minutes to complete. The participants in this pretest did not consider the length of the questionnaire to be a problem. In fact, many participants volunteered additional information. The study was approved by the Institutional Review Board at each of the three participating centers (Research Triangle Institute, Indiana University, and Pittsburgh Research Institute).
Statistical Analysis With use of our technique of stratified sampling, racial minorities and the elderly were intentionally oversampled. As a result, these minority groups were represented in numbers that were disproportionate to those in the underlying population. Therefore, it was necessary to assign a weight to each observation, or response on the survey, so that the results of the analyses would apply correctly to the general population. The weight was determined on the basis of the stratum to which the observation belonged, such that all observations from a given stratum were assigned the same weight. The stratum weight was calculated as: weight = (number eligible in the stratum/total number surveyed in the stratum) x (total population in the stratum/number of responses in the stratum), where the number eligible in the stratum refers to the number surveyed minus the number of individuals who had died or were found to be ineligible according to predefined criteria (already discussed). With this methodology, the weighted analyses produced results that correctly represented the underlying population. The three samples were analyzed separately, with independent sampling frames and weights. At no time were the three samples combined, as the number of individuals represented by each individual in the samples from western Pennsylvania and Indiana, based on the weights relative to the national sample, was relatively small. To ensure that the respondents were representative of the entire sample (that is, to ensure that there was no responder bias), respondents and non-respondents within each sampling stratum and within each sample were compared with use of chi-square statistics. Stepwise multiple linear-regression analysis was used to evaluate the factors related to the pain in the knee, physical function, and satisfaction with the knee replacement. Separate models were fit to each of the three outcomes (pain, physical function, and satisfaction) for each of the three survey samples in order to allow for comparisons among the samples. The independent variables included demographic characteristics, pain and physical function before the knee replacement and at the time of the survey (depending on the dependent variable being assessed), the number of patient-reported comorbidities, the year of the operation, the patient's reasons for having the operation, the type of health-insurance coverage (supplemental insurance or Medicaid, or both, in addition to Medicare), previous or subsequent operations on the involved knee, other medical problems related to the lower extremities that limited activity, the body-mass index at the time of the survey, and the scores for the eight subscales on the SF-36. Income was not included as a variable because of the high number of participants who did not respond to that item. Occupational status was excluded as most of the participants were retired. The body-mass index at the time of the knee replacement was closely correlated with that at the time of the survey (r = 0.87, p = 0.0001), so only the latter was used in the regression analyses. All independent variables that showed a significant association with the dependent variable in bivariate analyses were included in the final set of variables. All comparisons were performed with use of a two-tailed test at the 5 per cent significance level.
Rates of Response
Characteristics of the Respondents
Approximately 92 per cent (448) of the 487 respondents in the national sample described themselves as being retired, working as a full-time homemaker, or working on a volunteer basis before the knee replacement. Fewer than 5 per cent (seventeen) of the patients indicated that they were employed, none indicated that they were unemployed, and 11.1 per cent (fifty-four) indicated that they were disabled or unable to work. At the time of the survey, fewer individuals were employed (p = 0.02) or were disabled (p = 0.03) and more were retired (p < 0.0001) or were working on a volunteer basis (p = 0.004) than had been before the replacement. Most (472) of the 487 participants had been living independently before the knee replacement, but women were more likely to have been living alone (130 [41.3 per cent] of 315 women had been living alone compared with sixteen [9.3 per cent] of 172 men; p < 0.0001). Only 3.1 per cent (fifteen) of the participants had lived in an institution. No significant change in the living arrangements could be detected at the time of the survey. Although pain in the knee was the most common reason for the replacement (it was cited by 411 [84.4 per cent] of the participants), 191 participants (39.2 per cent) cited the inability to carry out their usual activities, 138 (28.3 per cent) cited unsteadiness with weight-bearing, 126 (25.9 per cent) cited the inability to carry out social and recreational activities, and fifty-four (11.1 per cent) cited the inability to work. No significant differences could be detected among these responses with regard to age, gender, or race.
Pain in the Knee and Physical Function
Before the Knee Replacement
At the Time of the Survey The participants reported significantly better ability to walk (p < 0.004) and to use stairs (p < 0.0001) and used fewer assistive devices (p = 0.01) than they had before the knee replacement (Table IV). One hundred and eighty-nine (38.8 per cent) of the 487 patients could walk more than ten blocks, and fifty-five (11.3 per cent) could walk at least five blocks. Only fifteen patients (3.1 per cent) were unable to walk at the time of the survey. Seventy-one (18.6 per cent) of the 382 participants who had to use stairs on a regular basis could do so without the use of a handrail, and 281 (73.5 per cent) could do so with the use of a handrail. Overall, thirty (6.2 per cent) of the 487 patients reported that they were unable to use stairs. Two hundred and ninety-three patients (60.2 per cent) could get around without the use of assistive devices, 193 (39.6 per cent) could get around with the use of assistive devices, and only one (0.2 per cent) was unable to get around at all. In the national sample, women reported a greater use of assistive devices (p = 0.03) and had greater difficulty with stairs (p = 0.001) than men did.
More than half of the respondents reported having either no or little difficulty when performing any of the seventeen activities assessed with the WOMAC (Table V).
Determinants of Pain and Physical Function after the Knee Replacement Two hundred and fifteen (44.1 per cent) of the 487 patients reported musculoskeletal problems that limited activities, and 217 (44.6 per cent) reported problems with the contralateral knee. Fifty-five participants reported having had an additional operation on the involved knee: twenty-six had had a revision and twenty-nine had had some other operation. One hundred and ninety-eight patients (40.7 per cent) had had an operation at some time on the contralateral knee, twenty-five had sustained a fracture of the hip, and fifty-eight had had a hip replacement. The scores for global health perception on the SF-36 and the number of patient-reported comorbidities that limited activities were similar for men and women. In the national sample, only one variable—the patient's rating of the severity of disease in the contralateral knee at the time of the survey—was a consistent predictor of the scores for physical function on the WOMAC. Age, gender, and subsequent operations on the involved knee were not significant independent predictors of physical function at the time of the survey. However, the scores for physical function were worse for participants in whom the index knee replacement was a revision (Indiana sample only, p = 0.0012), participants who had a greater body-mass index (Indiana sample, p = 0.02; western Pennsylvania sample, p = 0.01), and participants who had had the prosthesis in place for a longer period of time (western Pennsylvania sample only, p = 0.02).
Patient-Reported Improvement in the Knee and Satisfaction with the Knee Replacement
Knee replacement was found to be effective for the relief of pain and the improvement of physical function for as long as seven years postoperatively in a large random sample of patients who were thought to be representative of the United States population of Medicare recipients. The present study included patients from teaching and non-teaching centers, patients from urban and rural communities, and patients who were very elderly (more than eighty-five years old). Although knee replacement had less of an impact on physical function than on pain (reflecting the high prevalence of medical comorbidities such as generalized osteoarthrosis), most patients believed that the knee was improved after the knee replacement. Our findings were generally consistent across the three independent samples that were studied, and most patients were satisfied with the result of the knee replacement. The findings of the present community-based study confirm the excellent results that have been reported in association with knee replacements done at tertiary-care centers by surgeons who perform a high volume of such operations17,18. A recent meta-analysis of the literature on knee replacement revealed a favorable outcome for almost 90 per cent of patients4,5. That analysis was based primarily on studies that were composed of small cohorts of selected patients (average, sixty-four patients per cohort), and 70 per cent of the institutions were teaching hospitals. Numerous factors, such as revision, obesity, and advanced age, have been reported to have an adverse effect on the outcome of knee replacement4,5,21,32,33,35. In the present study, multivariate analyses were used to identify the predictors of optimum patient-relevant outcomes after knee replacement; the identification of such predictors is necessary for the development of practice guidelines. The most striking finding of our study was that relatively few patient-related characteristics were associated consistently with pain or function at the time of the survey. Approximately 5 per cent of the patients in the present study had a revision knee replacement as the index procedure. Revision knee replacement was found to be associated with greater difficulty performing activities in the Indiana sample only. Furthermore, the patients in the national sample for whom the index replacement was a revision were less satisfied with the result of the operation, whereas the patients in the western Pennsylvania sample for whom the index procedure was a revision were significantly more satisfied with the result. This discrepancy may reflect geographic differences in patients' expectations regarding the outcome of revision knee replacement, possibly as a result of variations in physicians' attitudes and perceptions regarding the effectiveness of this procedure. We were unable to determine whether patients for whom the index replacement was a revision had had more previous operations on the involved knee than patients for whom the index replacement was a primary procedure. The effect of obesity on the outcome of knee replacement is unclear21,32,33,35. In a recent survey of orthopaedic surgeons practicing in Indiana, more than 90 per cent of the respondents reported that a patient could weigh too much to be considered a candidate for a knee replacement36. Previous authors have reported that morbid obesity (a body-mass index of at least thirty-two kilograms per square meter) was not associated with an increased frequency of postoperative complications after controlling for age, race, and comorbidity25,35. In the present study, a greater body-mass index was associated with worse physical function in the Indiana and western Pennsylvania samples, but it was not a significant predictor of pain or of the need for a subsequent revision for as long as seven years after the index operation. Thus, although the outcome for obese patients may not be as good as that for non-obese patients, a replacement does provide relief of pain for obese patients who have advanced osteoarthrosis of the knee. The findings of the present study suggest that obesity may not be a contraindication to knee replacement. Studies with longer follow-up are needed to determine conclusively whether obesity is a predictor of a worse outcome after this procedure and to assess whether it is associated with earlier failure of the prosthesis. The findings of previous studies have suggested that the outcome of knee replacement is worse for older patients than for younger patients2,4. In the survey of orthopaedic surgeons practicing in Indiana, 25 per cent of the respondents reported that a patient could be too old to be a candidate for knee replacement36. Such perceptions could result in reduced access to knee replacement for elderly patients. In the present study, elderly patients (those who were at least eighty years old) who responded to the survey had had similar relief of pain and were not more likely to have had a revision or another operation on the involved knee compared with younger patients. Elderly patients also reported similar levels of function at the time of the survey, were equally likely to report that the knee was improved compared with the preoperative status, and were equally satisfied with the outcome of the procedure. Thus, advanced age is another factor that does not appear to be a contraindication to knee replacement. Pain was the primary reason cited by the participants for having the knee replacement; this finding emphasizes the importance of considering patient-reported symptoms in addition to measures of functional performance (such as the duration for which the patient can walk and the range of motion of the joint) when evaluating the outcome of knee replacement. Fewer than 2 per cent (twenty-two) of the 1193 randomly sampled patients reported that they had had no pain before the operation. Furthermore, most patients reported that the pain was severe and that it was associated with poor physical function and a reduced quality of life (as measured by the ability to socialize and carry out their usual activities). Thus, the prevalence of potentially inappropriate knee replacements in this population appeared to be low. There was a marked difference between men and women with regard to the status of the involved knee before the replacement. Women reported, on average, more pain and disability and used more medications for pain and swelling of the knee than men did. Women also reported a greater degree of disability at the time of the survey, even though the frequency of concomitant musculoskeletal problems in women was similar to that in men. Similar discrepancies between men and women consistently have been noted in epidemiological studies in which standardized generic and disease-specific health-status instruments were used to evaluate patients who had had a joint replacement or some other operative procedure. Katz et al.23 found that women who had had a hip or knee replacement reported greater pain and functional limitations than men did; similar findings were reported for patients who had had a laminectomy. In contrast, Gabriel et al.15, using both clinical and radiographic criteria, found no significant difference between men and women with regard to the severity of osteoarthrosis of the hip before total hip arthroplasty. The reasons for the discrepancies in the present study are not known but may include differences between men and women with regard to their recall of the status of the knee at the time of the operation, differences in their reasons for having a knee replacement, and the fact that more women were living alone and thus potentially were less able to rely on others for assistance with daily activities. The present study has several limitations, many of which are well recognized shortcomings of retrospective patient-based surveys. First, we relied on the ability of patients to recall the status of the knee in the four weeks before the knee replacement, which had been performed two to seven years previously. As we were sensitive to the possibility of recall bias, we focused our analyses primarily on the determinants of pain and physical function at the time of the survey and only secondarily on the patient-reported changes in pain and function since the operation. Even if we disregarded all patient-derived information based on recall, we would still conclude that patients were highly satisfied with the result of the knee replacement and had acceptable levels of pain and physical function as long as seven years after the operation. Second, because we considered only Medicare recipients who were sixty-five years old or more, we cannot comment on the outcome for younger patients who had a knee replacement during the period of study. However, approximately three-quarters of all knee replacements in the United States are performed for patients who are at least sixty-five years old23, so our study population represents the overwhelming majority of patients who have this procedure. Third, because our results are based on reports from patients, we cannot comment on the extent to which the quality of the operation, the type of knee replacement performed, or the volume of knee replacements performed by the surgeon may have affected the outcome. Fourth, by excluding patients who had died before the survey, we may have biased our results in favor of more positive outcomes if the deceased patients had had worse outcomes. Fifth, although the patients had had the replacement as long as seven years earlier, studies with longer follow-up are needed in order to examine long-term results of knee replacement, especially with regard to the need for revision. Finally, the results were not identical for all three sites. However, there was general agreement among the sites with respect to the direction, if not the magnitude, of the influence of the explanatory variables. In the present community-based study of a representative sample of Medicare recipients, knee replacement was found to be effective for the treatment of pain and physical dysfunction caused by osteoarthrosis of the knee. Patients who participated in the survey reported marked relief of pain (the most frequently cited indication for the knee replacement) as well as improved physical function for as long as seven years after the procedure. As the population of the United States ages, the prevalence of advanced osteoarthrosis of the knee is expected to increase. Our findings support the use of knee replacement for the treatment of this condition. Specifically, our findings that age and obesity do not seem to have a negative impact on patient-relevant outcomes suggest that it may be inappropriate to not recommend or perform a knee replacement because of the age or weight of the patient. Because we are living in an era in which the primary-care physician increasingly serves as the gatekeeper to specialty care and because patients' attitudes and perceptions regarding knee replacement are largely shaped by their personal experiences and by the opinions and beliefs of their physicians, both primary-care physicians and orthopaedic surgeons need to be aware of the findings of the present study.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding sources were Grant 06432 of the Agency for Health Care Policy and Research to Indiana University and subgrantees (University of Toronto, Research Triangle Institute, Pittsburgh Research Institute, and University of Indiana) and Medical Research Council Scholarships (G. H. and J. W.).
#Care Management Division, Clinical Economics Outcomes Assessment, Glaxo Wellcome, 5 Moore Drive, Research Triangle Park, North Carolina 27709. **Vanderbilt Medical Center, Seventh Floor, Medical Center East, Nashville, Tennessee 37232.
##541 Clinical Drive, Room 600, Indianapolis, Indiana 46202-5111. ***Office of Academic Affairs, Bryan Hall, Room 109, Indiana University, Bloomington, Indiana 47405.
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