Medical Effectiveness/Outcomes Research

Total Knee Replacement PORT publishes recent findings

The volume of total knee replacements (TKRs) performed in the United States reached 150,000 in 1990, with expenditures of $3.5 billion. Hospital costs alone for knee implants are about $9,000 per procedure, exclusive of physician fees and rehabilitative treatments. Patients with advanced joint destruction who undergo TKR usually experience pain relief and increased joint mobility, but long-term benefits are much less certain.

The Total Knee Replacement Patient Outcomes Research Team (PORT) is supported by the Agency for Health Care Policy and Research (HS06432) to assess and improve the outcomes of this procedure. Led by Deborah A. Freund, Ph.D., of Indiana University, the PORT investigators recently published three studies. They compare rural with urban costs for TKRs, calculate the rates of tibial osteotomies in Canada and the United States, and compare the usefulness of general and specific measures to assess health-related quality of life following TKR.

Culler, S.D., Holmes, Ann M., and Gutierrez, B. (1995). "Expected hospital costs of knee replacement for rural residents by location of service." Medical Care 33(12), pp. 1188-1209.

Knee replacement surgery, which improves the functional mobility of persons with severe arthritis, is rapidly diffusing into rural hospitals. The predicted cost per TKR is lower in rural than urban hospitals, especially in hospitals that do a large number of TKRs, according to this study by TKR PORT researchers. They analyzed 1985-1989 data from the Health Care Financing Administration's Medicare Provider Analysis and Review and found that cost savings ranged from $1,560 (for a Medicare patient discharged home with average severity of illness) to $6,306 (for hospitalization of a Medicare patient with multiple knee replacements and high severity of illness).

The higher the hospital's TKR case volume, the greater the cost savings. For example, the median volume of knee replacements for rural hospitals was nine per year, with an average cost per hospitalization of $8,690. By increasing the hospital's volume even by one knee replacement per year, the predicted cost per case fell $48. This incremental cost savings declined as volume increased for both urban and rural hospitals, although the incremental effects remained greater in rural hospitals. Also, the significant cost savings that can be achieved by moving patients from low- to high-volume hospitals in each setting provides support for regionalization of TKR surgery. For instance, more than $1,000 per hospitalization can be saved if a rural patient has knee replacement surgery in a rural hospital performing nine or more TKRs per year, compared with one in which only a single surgery is performed each year.

Wright, J., Heck, D., Hawker, G., and others (1995, October). "Rates of tibial osteotomies in Canada and the United States," Clinical Orthopaedics, pp. 266-275.

Tibial osteotomy, one surgical option for treating osteoarthritis of the knee, has declined as TKR surgery has increased over the past decade. Osteotomy shifts the axis of weightbearing onto a more normal joint surface and lessens pain in about 80 percent of patients. Disadvantages of this procedure include incomplete relief of pain, and there is a 50 percent rate of pain recurrence 10 years after osteotomy. TKR, on the other hand, does not allow patients to return to vigorous sports or heavy labor, and there is a possibility of loosening the prosthesis. For these reasons, tibial osteotomy still may be the most appropriate procedure for younger, active patients with primarily unicompartmental osteoarthritis who want to participate in vigorous physical activity, according to TKR PORT researchers.

They calculated the rates of tibial osteotomies performed from 1985 to 1990 in Ontario, Canada, and the United States, using data from the Health Care Financing Administration, Ontario Health Insurance Plan, and National Hospital Discharge Survey databases. They found that osteotomy rates decreased in both countries by about 11 to 14 percent per year in patients 65 years and older and by 3 to 4 percent per year in patients younger than 65 years. Men received twice as many osteotomies as women in both countries. In the United States, the average rate of tibial osteotomies was two to three times lower than in Ontario, most likely due to different expectations and preferences of patients and/or surgeons. A portion of the decline in osteotomy rates in older patients may be a result of the increasing use of TKR and growing confidence among surgeons in TKR outcomes. Also, the longevity of the prosthesis is of less concern in older patients than in younger patients.

Hawker, G., Melfi, C., Paul, J., and others (1995). "Comparison of a generic (SF-36) and a disease specific (WOMAC) instrument in the measure of outcomes after knee replacement surgery." Journal of Rheumatology 22(6), pp. 1193-1196.

Measuring the health status of individuals with a particular medical condition is best achieved by using both specific health status measures relevant to the particular condition and generic measures of overall health status, particularly when assessing the health status of elderly persons who typically have several coexisting medical conditions. The Total Knee Replacement PORT investigators compared the generic health-related quality of life (HRQL) measure, the SF-36, with the disease-specific HRQL measure, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) in assessing the health status of nearly 1,200 Medicare patients who had undergone knee replacement surgery 2 to 7 years previously. The investigators accumulated data through a mail survey of self-administered questionnaires to three random samples of Medicare beneficiaries.

The SF-36 measured physical, role/emotional, and role/social functioning; bodily pain; vitality; and general health perceptions. The WOMAC, designed to assess hip or knee osteoarthritis, assessed stiffness, pain, and physical functioning. The SF-36 correlated better with patients' coexisting conditions than the WOMAC on all dimensions of pain, physical functioning, and overall scores. However, the WOMAC overall scores correlated better than the SF-36 scores with the current condition of the knee, rated from 1 or "much worse" to 5 or "much better." The researchers conclude that generic measures are necessary to compare outcomes across different populations and different diseases, whereas disease-specific measures assess the specific disabilities of patients in defined diagnostic groups.

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