Treatment is proposed for patients based on the assumption that patients will, on balance, have more benefit than harm. Prognostic factors influence the probability of response, remission, recurrence and duration of disease under clinical care.15
Determining prognostic factors that affect treatment effectiveness is essential to clinicians and important to patients in their decision-making. Physicians report that patient characteristics do
affect their decisions either to refer patients for or recommend knee arthroplasty; yet, how
patient characteristics influence their recommendations varies substantially.5,7
Despite variation in physician opinion, our systematic review found little consistent evidence on the nature and magnitude of the influence of patient characteristics on the outcomes of pain, revision, function and mortality after total joint arthroplasty. Furthermore, even if certain subgroups fare less well after total joint arthroplasty, this does not mean that, on average, these patients did not receive benefit from the procedure. The major finding of our review suggests that, despite the impressions of referring physicians and surgeons,5,7
patients should in general not be restricted access to total joint arthroplasty based on their characteristics.
On the other hand, decision-making requires discussion of the risks and benefits of treatment tailored to the patient and his or her circumstances. The results of this study suggest that certain factors, even in the context of low risk and overall improvement in quality of life, do affect outcome. Older patients, particularly men, need to know that, although the absolute differences are small, their risks of revision and mortality for both hip and knee arthroplasty are higher. Although they vary by study, most results seem to suggest higher revision rates for both femoral and acetabular components. Older age was also associated with poorer functional outcome relative to younger patients. The exact age at which this relative decrease in improvement occurs was not adequately described, because the ages described as “younger” ranged from younger than 50 to younger than 75. Furthermore, and more importantly, functional improvement relative to baseline occurred in all age groups. Thus although older patients may realize less benefit compared with younger patients, they are still candidates for arthroplasty and can expect, on average, an improvement in quality of life. Women who had hip arthroplasty had worse functional outcomes. However, this may have been due to their surgeries occuring at a more advanced stage of disease. Although lower function and satisfaction scores were reported among obese patients, obesity, which is generally assumed to adversely affect prosthesis longevity, did not increase revision rates in these studies. These findings are important in view of the many appropriate candidates who consider themselves to be “too old, too fat or too sick” for the procedure.
There is increasing recognition that the systematic reviews of clinical studies evaluating prognosis are not as straightforward as randomized controlled trials.45
Nevertheless, great strides in the methodologies for evaluating quality and combining data from prognostic studies have been developed.45
Numerous factors, however, prevented us from summarizing studies in order to provide aggregated point estimates. These issues would likely be relevant to prognostic studies of most surgical conditions and therapies. First, many studies were derived from the same national registries (e.g., several studies used data from overlapping years), and thus we were unable to combine results among studies. Second, there was inconsistency with respect to the definition of various prognostic factors and outcomes. For example, the categorization of young or old varied by up to 20 years and on several occasions varied within studies based on the same registry data.16,17
Third, we observed that most studies assumed a linear relation between prognostic factor and patient outcome because regression analyses were almost always used. However, not all relations may be linear. Fourth, many studies did not take into account all important variables such as the extent of obesity, work status, physical activity, preoperative function or health status. Fifth, studies lacked consistent definition of key outcomes such as “joint failure” and the definition and verification of important postoperative adverse events or arthroplasty complications. Sixth, there are no subject terms specifically available to capture “prognosis” studies. The MeSH terms are imprecise in those bibliographic databases that use them (MEDLINE, CINAHL), but subject terms are very broad in EMBASE, which does not use MeSH terms. Finally, many of the studies identified in this systematic review were based on databases and registry data. These studies seldom reported the methods employed to minimize entry of false or incorrect data. Only a few studies reported use of double data entry, retrospective audits of hospital medical files or comparison to a national discharge registry. More often, we observed that there was discussion of the software and training of the entry personnel but not necessarily quality checks for the data collection.
Recognizing the limitations of prior research, an important question is whether future meta-analyses should or should not use the older studies such as those identified in this article. The updating of systematic reviews does not always add to the precision of pooled estimates or change the clinical interpretation.46,47
For example, some areas of research are more prolific than others, and thus time alone would not be sufficient criteria for updating a review.48
The quality of the literature is an important factor to consider. A review by Kane and colleagues49
did not find age, sex and obesity to be significantly correlated with knee arthroplasty outcomes; they too noted that few studies used any analysis to evaluate the relation between patient characteristics and functional outcomes. Ethgen and colleagues50
also conducted a systematic review to evaluate health-related quality of life in patients who had knee arthroplasties. They determined that age and weight did not affect improvement in functional outcomes. Although they suggested that men benefitted more from arthroplasty than women, the evidence to support this finding is not substantive. The qualitative summaries in both these reviews depict much variation in the influence of the patient characteristics. Despite the varied eligibility criteria in these other reviews, as in our systematic review, the studies do not show an unequivocal relation between the patient characteristics and outcomes. As identified in our review, the methodo-logic quality of all these studies is limited. The inclusion criteria for study patients were not always clearly specified, and they likely reflected the selection biases of surgeons. In addition, the operational definitions of some important outcomes such as pain were nonstandardized. Thus we believe future reviews or meta-analyses should not include studies from an older chronological period because this typically magnifies methodologic limitations.
Our study has several specific limitations. First, we limited our review to patients with osteoarthritis; therefore, extension of the findings to other diagnoses such as rheumatoid arthritis may be limited. Second, our review included only studies with a sample size of 500 or more patients. Because our initial search yielded more than 14 000 citations, we considered such a restriction to be necessary to yield a manageable number of studies. This may have resulted in the exclusion of some studies that might have provided useful information. However, given the limitations of the literature noted above, we do not believe these studies would dramatically affect our conclusions. Third, we did not perform manual searches of relevant journals or contact organizations to identify additional studies or unpublished work meeting our eligibility criteria.
In conclusion, the results of this study suggest that subgroups of patients, particularly men and older patients, are at higher risk of death and revision following total joint arthroplasty. The risks were higher in some subgroups than others, but overall risks for all groups remained very small. Thus in no specific subgroup of patients did total joint arthroplasty appear contraindicated. This is relevant to decision-making since many physicians often advise the patients they are too old or obese to receive total joint arthroplasty. Future studies are needed to address the methodologic limitations identified in this study to more clearly advise patients and doctors on how patient characteristics affect the outcome of total joint arthroplasty.