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Knee Replacement

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Full Title: Total Knee Replacement

December 2003

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Structured Abstract

Context: The projected growth in the population with arthritis is likely to expand the future demand for elective arthroplasty. At present, there is no strong empirical base for the indicators in current use for what criteria should be used to identify potential candidates for Total Knee Arthroplasty (TKA)*; nor is there professional consensus around such indications. A National Institute of Health (NIH) consensus conference has been planned to address these questions. This report summarizes the literature as part of the background for that conference.

Objectives: A systematic review of the literature was undertaken to address the following questions:

  1. What are the current indications for, and outcomes from, primary total knee replacement?
  2. How do specific characteristics of the patient, material and design of the prosthesis, and surgical factors, affect the short-term and long-term outcomes of primary total knee replacement?
  3. Are there important perioperative interventions that influence outcomes?
  4. What are the indications, approaches, and outcomes for revision total knee replacement?
  5. What factors explain disparities in the utilization of total knee replacement in different populations?
  6. What are the directions for future research?

Data Sources: The primary TKA literature search was performed by the National Library of Medicine, which searched PubMed® from 1995 to April 2003. The access search was done using PubMed and covering the period from 1990 through April 2003. The literature search on revisions was done in two stages. A prior MEDLINE® search covering the period from 1996 through 2000 was the basis for a meta-analysis. An updated search using PubMed® covered 2001 through April 2003.

Study Selection: The nature of this topic required heavy reliance on observational studies. The major criteria for identifying studies for inclusion in the indications for TKA search required that they address primary TKAs, have at least pre and post surgery data using at least one of four standard functional measures (Knee Society [KS] score, Hospital for Special Surgery [HSS] score, WOMAC, or SF-36), have a sample size of at least 100 total knee replacements, be published in English, and utilize tricompartment TKA. Sixty-two studies met the full inclusion criteria. The selection of studies on access required that they examine the relationship of at least gender or race to the performance of primary TKAs. Six articles were included. The same inclusion criteria applied to primary TKAs were applied to the update of the TKA revision study. Fourteen articles met the criteria.

Main Results: Both TKA and total knee arthroplasty revision (TKAR) are associated with improved function. The strongest evidence exists over a followup period of up to two years, but the studies that extend to five and even ten years of followup show positive results as well. The average age of patients undergoing TKA in these reports was 70 years with few over aged 85. Two-thirds were female, one third were considered obese, and nearly 90% had osteoarthritis. No studies provided data on racial/ethnic status. The mean effect size (expressed as numbers of standard deviations) is considered large in magnitude and varies from 1.6 to 3.9 depending on the functional measure used and the duration of followup.

There is no evidence that age, gender, or obesity are strong predictors of functional outcomes. Patients with rheumatoid arthritis show more improvement than those with osteoarthritis, but this may be related to their poorer functional scores at the time of treatment and hence the potential for more improvement. The revision rate through five or more years is 2.0% of knees and 2.1% of patients.

Complications as defined by the investigator occurred in 5.4% of patients and 7.6% of knees. Patients with rheumatoid arthritis show more improvement than those with osteoarthritis.

With regard to access, nonwhites receive TKAs less often than whites despite higher rates of osteoarthritis. Women receive TKAs more often than men, but the pattern is not as consistent as with race.

TKA revisions are associated with consistent improvement in function on an order of magnitude similar to primary TKAs.

Conclusions: In general, the outcomes research on TKAs emphasizes before and after studies that are variations on case series of various techniques and prostheses with little attention to the role of other factors or to attrition. Although demographic and clinical factors are recorded, they are rarely used in the analysis. A consistent body of evidence suggests substantial improvement in function associated with TKA and TKAR. The followup periods vary but the mean is greater than five years. More informed decision making about indicators for TKAs will require stronger research designs. These need to be planned as prospective studies with multivariate analysis. Such analyses will require larger samples and more consistent and comprehensive data collection than was found in this review.

*The term "total knee arthroplasty" is used instead of "total knee replacement" because the abbreviation is frequently confused with total knee revision.

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Total Knee Replacement

Evidence-based Practice Center: Minnesota
Topic Nominators: National Institute of Health (NIH) Office of Medical Applications of Research, and the National Institute of Arthritis and Musculoskeletal and Skin Diseases

Current as of December 2003


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