 |
 |
 |
|
| home | CME | help | feedback | subscriptions | archive |
|
© 1996 The Journal of Bone and Joint Surgery, Inc. Improvement in Cardiovascular Fitness after Total Knee Arthroplasty* , COOPERSTOWN, NEW YORKInvestigation performed at The Mary Imogene Bassett Hospital, Cooperstown
Patients who have osteoarthrosis involving weight-bearing joints typically have a gradual decline in physical activity, which is often associated with cardiovascular deconditioning. After joint replacement, many patients resume routine walking and recreational activities, which may improve aerobic capacity. The purpose of the present study was to determine the effect of total knee arthroplasty on cardiovascular fitness. Nineteen patients who had had total knee arthroplasty (the arthroplasty group) performed an exercise test for cardiovascular fitness preoperatively. Sixteen of these patients were tested again at one year postoperatively and thirteen, at two years postoperatively. Sixteen patients in whom osteoarthrosis of the knee was being treated medically (the control group) were tested at the time of enrollment in the study and one year later. Nine of these patients also were tested two years after enrollment. All of the patients completed the Arthritis Impact-Measurement Scales (AIMS) at each examination. Fitness was assessed by the performance of a progressive maximum exercise test with use of a bicycle ergometer and a metabolic cart. All patients achieved the anaerobic threshold. One year postoperatively, the patients in the arthroplasty group demonstrated an increase, which approached significance, in maximum oxygen consumption (measured in milliliters of oxygen per minute) (p = 0.07), maximum oxygen consumption corrected for body weight (p = 0.08), and percentage of predicted maximum uptake of oxygen (p = 0.06). Two years after the total knee arthroplasty, the patients had a significant improvement with regard to all three parameters (p = 0.008, 0.005, and 0.005, respectively). The patients in the control group demonstrated a significant decrease in duration of exercise and in maximum workload at one year (p = 0.003 and 0.005, respectively) and at two years (p = 0.008 for both parameters). Physical activity had increased in the arthroplasty group but not in the control group, as demonstrated by the results of the Arthritis Impact-Measurement Scales. These findings demonstrate a trend toward improvement in cardiovascular fitness one year after total knee arthroplasty and a significant improvement two years postoperatively for patients who had been able to resume routine functional activities because of the arthroplasty. These improvements compared favorably with the static pattern or the decline in the measures of fitness that were observed in the control group. Our results should be considered preliminary because of the relatively small number of patients who were studied.
Patients who have symptomatic osteoarthrosis of the knee typically are overweight and have less strength, endurance for exercise, and aerobic capacity than patients who do not have osteoarthrosis2,5,11,14,20,25. Some of these effects may be due to systemic manifestations of the disease, particularly in patients who have inflammatory osteoarthrosis. However, the physical deconditioning that is associated with osteoarthrosis appears to result from a progressive decline in functional activities due to osteoarthrotic pain. We observed an association between the severity of gonarthrosis and the severity of cardiovascular deconditioning26 as well as between impaired fitness and a trend toward a higher prevalence of coronary heart disease among patients who had been assessed immediately before total knee arthroplasty25. A sedentary lifestyle, particularly for an elderly individual, is associated with cardiovascular deconditioning and an increased risk for development of the manifestations of coronary heart disease4,6,22. However, even modest increases in walking activity can improve the fitness of patients who have cardiovascular deconditioning10,19. Kovar et al. demonstrated that exercise sessions consisting of one-half hour of walking, three times a week for eight weeks, improved the six-minute walking distance for patients who were being treated medically for gonarthrosis13. Weight-bearing exercise may not be feasible for patients who have severe osteoarthrosis that is being treated non-operatively. However, after total knee arthroplasty, most patients resume routine walking and recreational activities that were not possible before the operation. Current trends in health care have focused on the costs and benefits of new as well as conventional orthopaedic treatments. The benefits of total knee arthroplasty, in terms of relief of pain, restoration of the function of the joint, and satisfaction of the patient, are well documented. However, the impact of operative treatment on health, fitness, and the risk of coronary heart disease has not been specifically addressed, to our knowledge. The purpose of the present study was to determine the effect of total knee arthroplasty on cardiovascular fitness.
Cardiovascular fitness was assessed for two groups of patients with osteoarthrosis of the knee who were followed for as long as two years. One group had total knee arthroplasty (the arthroplasty group), and the other group was treated medically (the control group). The patients in the arthroplasty group were recruited by mail. A letter describing the study was sent to a consecutive series of patients who were scheduled for primary total knee arthroplasty. Patients who had revision total knee arthroplasty or another operation during the study period were excluded. The patients in the control group were recruited through an advertisement about the study that was posted in the rheumatology clinic. In order to be eligible to participate, patients had to be more than fifty years old and had to have symptomatic osteoarthrosis involving one knee or both. All of the patients in the control group were examined by a rheumatologist (G. D. G.) and had had a radiograph made of the knee within one year before they entered the study. At the time of their enrollment in the study, none of the patients in the control group were considered by their treating physician to be a candidate for total knee arthroplasty. If the symptoms in the knee of a patient in the control group became worse during the period of the study so that operative treatment was indicated, the patient was excluded from the study. All of the patients in the study met the criteria of the American Rheumatism Association1 for a diagnosis of osteoarthrosis of the knee. No patient in either group was excluded because of the severity of the deformity of the joint or because of pain. Patients who volunteered to participate in the study were asked to perform a test for cardiovascular fitness at the time of enrollment in the study and to return to repeat the test both one and two years later. The patients in the arthroplasty group had preoperative testing before donating autologous blood. During the study period, we made no recommendations to the patients in either group regarding regular aerobic exercise or fitness training. The present study was approved by the Institutional Review Board of our hospital, and all patients signed an informed-consent form. Cardiovascular fitness was assessed with a so-called maximum symptom limited cardiopulmonary exercise test. The patients fasted for eight hours before performing the exercise test. Multichannel electrocardiograms and blood pressure were monitored before, during, and after exercise. Patients performed progressive exercise with use of a semi-upright bicycle ergometer (Quinton, Seattle, Washington) with an incremental increase in workload every sixty seconds. Patients were asked to exercise for as long as they were able to do so. Bicycle ergometry was chosen because this method relieves weight-bearing stresses that occur with treadmill exercise, and it had been used successfully by two of us (E. F. P. and M. D. R.) in a study of patients who had severe osteoarthrosis of the knee24. Patients who were incapable of performing exercise with the lower extremities used the upper extremities to perform the same protocol with the same device. The exercise protocol during follow-up examinations was the same as that performed on entry into the study. The electrocardiograms during the exercise were interpreted as indicating ischemia if there was ST-segment depression of one millimeter or more at 0.08 second beyond the J point (the junction between the S wave and the ST segment on the electrocardiogram). All exercise tests were supervised by a cardiologist (E. F. P.). Cardiopulmonary function was assessed during the exercise with use of a metabolic cart (CPX-MAX; Medical Graphics, St. Paul, Minnesota), which analyzed inspiratory and expiratory gases on a breath-by-breath basis in order to determine oxygen consumption, carbon dioxide production, and minute ventilation. The respiratory exchange ratio and the oxygen pulse were also monitored during the test. Oxygen consumption at the anaerobic threshold was determined with use of the method of Beaver et al.3. The primary indicator of cardiovascular fitness was oxygen consumption (in milliliters of oxygen per minute) at peak exercise. As the age and gender of a patient can affect maximum oxygen consumption, the oxygen consumption by each patient at peak exercise was compared with the predicted value, with use of a regression formula that was based on age and gender9, and was expressed as a percentage of the calculated value. Other indicators of cardiovascular fitness were maximum oxygen consumption corrected for body weight (in kilograms), duration of exercise (in seconds), and maximum exercise workload (in watts). The Arthritis Impact-Measurement Scales, a self-administered questionnaire17,18, was completed by all patients at each examination for cardiovascular fitness. The questionnaire provides a validated assessment of health status and activity for patients who have osteoarthrosis16. By choosing a single answer from five options, patients answered questions in seven general categories (level of mobility, walking and bending, self-care, performance of household tasks, osteoarthrotic pain, satisfaction, and over-all impact of the osteoarthrosis). The scores were standardized to values of 0 to 10 points, with higher numbers representing a poorer health status. Nineteen patients in the arthroplasty group were tested before the operation. Sixteen of them had follow-up testing one year after the arthroplasty. Thirteen of the nineteen patients had follow-up testing two years after the arthroplasty. Ten patients completed follow-up testing both one and two years after the arthroplasty, six patients completed testing at one year but not at two years, and three patients completed testing at two years but not at one year. Sixteen patients in the control group performed the test on entry into the study and also one year later. Nine of the sixteen patients also had follow-up testing two years after the initial assessment. The patients in both groups who did not return for the one or two-year follow-up examination said that the major reasons for not participating were the inconvenience of travel, the time needed for testing, and scheduling conflicts. A personal computer was used to enter data, which were archived and analyzed with use of commercially available software (Q & A; Symantec, Cupertino, California, and True Epistat; Epistat Services, Richardson, Texas). The chi-square test and the Fisher exact test were used to compare differences in categorical values within and between the groups. The non-parametric Wilcoxon signed-rank test was used to compare differences in ordinal and continuous measures within and between the groups. Because the patients in both groups differed with regard to the severity of the osteoarthrosis and the ability to perform the exercise test with the lower extremities, no direct statistical comparisons of the major dependent variables were made between the groups. Statistical comparisons of the results of the exercise tests and the scores on the Arthritis Impact-Measurement Scales were limited to comparisons within each group at the one and two-year follow-up evaluations. In all cases, a two-tailed p value of 0.05 or less was considered to be significant.
Although the patients in the control group were not individually matched to those in the arthroplasty group, there were no differences in the mean age, weight, or body-mass index, or in the distribution with regard to gender, type of osteoarthrosis, or medical history (Table I). All patients achieved the anaerobic threshold, indicating that pain in the joint did not limit the capacity for exercise. Thus, the results demonstrated an assessment of maximum exercise effort and maximum aerobic capacity.
One year postoperatively, the arthroplasty group demonstrated increases that were near significance for maximum oxygen consumption (p = 0.07), maximum oxygen consumption corrected for body weight (p = 0.08), and percentage of predicted maximum oxygen consumption (p = 0.06) (Table II). Two years after the arthroplasty, the patients demonstrated significant improvements in each of the variables (p = 0.008, 0.005, and 0.005, respectively). The mean percentage of predicted maximum oxygen consumption (85 per cent) was less than the normal value31 before the operation. It improved to the normal range after the arthroplasty.
The control group had no significant changes in maximum oxygen consumption or in maximum oxygen consumption corrected for body weight. The mean percentage of predicted maximum oxygen consumption was within the normal range for these patients at the start of the study and did not decrease at the one or two-year follow-up examination. The control group demonstrated a significant decrease in duration of exercise and in maximum workload at one year (p = 0.003 and 0.005, respectively) and at two years (p = 0.008 for both) (Table III).
The scores on the Arthritis Impact-Measurement Scales for the control group demonstrated no significant changes during the study period, with the numbers available (Table III). However, the patients in the arthroplasty group had a significant improvement in the scores for mobility, walking and bending, performing household tasks, osteoarthrotic pain, satisfaction, over-all impact of the osteoarthrosis (a patient's perception of how the osteoarthrosis affects him or her relative to the function of a person of the same age), and impact of the osteoarthrosis (a patient's perception of the effect of the osteoarthrosis on mobility, walking and bending, and so on) at both one and two years after the operation (p  0.05) (Table II).
The orthopaedic literature has been the subject of criticism because clinical researchers often have described the technical aspects of operative intervention and the impact of an operation on the function of a specific joint rather than on the over-all physical and economic status of the patient7. The ideal assessment of the outcome of an operative procedure, therefore, is based on a comparison with a control group of patients who have the same diagnosis but are managed non-operatively. Although outcome studies can be used to compare the function and satisfaction of the patient postoperatively with the condition of the patient preoperatively27, to our knowledge no investigators have compared the results of total knee arthroplasty in one group of patients with those for a similar group of patients who were managed non-operatively. However, withholding operative treatment from patients who have appropriate indications for arthroplasty is unethical. For this reason, we chose a control group of patients who had the same underlying diagnosis as the patients who had had total knee arthroplasty but who had symptoms that were not severe enough to warrant operative intervention. By following each group of patients independently for two years, we were able to assess the effects of both medical and operative treatment on cardiovascular fitness and health. The feasibility of patients who have osteoarthrosis performing exercise tests has been questioned because pain in the joint may limit muscular effort. However, oxygen consumption and the energy cost of locomotion are increased in such patients30. The inefficiency of the osteoarthrotic joint and the increased work that is necessary to move it may, therefore, contribute to the ability of the patient to reach maximum cardiovascular effort before pain in the joint develops and limits muscular effort. Oxygen consumption at the anaerobic threshold and oxygen consumption at peak exercise are measures of cardiovascular fitness29. As all patients in this study achieved the anaerobic threshold, the results demonstrate an assessment of maximum exercise effort and maximum aerobic capacity. In the control group, exercise testing at the time of enrollment indicated a baseline level of fitness that was equal to or greater than that in the arthroplasty group. The baseline scores on the Arthritis Impact-Measurement Scales also indicated that functional impairment was not as severe in the control group as in the arthroplasty group. These findings are consistent with the observation that more severe gonarthrosis is associated with a greater degree of cardiovascular deconditioning26. Decreases in duration of exercise and in maximum workload without a substantial change in maximum oxygen consumption or in maximum oxygen consumption corrected for body weight were observed in the control group. The decrease in the ability to perform muscular work, despite static measurements of cardiovascular fitness, suggests that patients who have medically treated osteoarthrosis have a decline in the efficiency of the musculoskeletal system. The score for osteoarthrotic pain in the arthroplasty group improved postoperatively to a level that was similar to that in the control group. The improved but abnormal scores for pain were attributed to musculoskeletal pain that had originated from sources other than the knee. The trend toward improvement in the measures for cardiovascular fitness one year after the operation, which reached significance two years after the operation, indicates that gradual physical reconditioning occurs postoperatively. The increased activity demonstrated by the results on the Arthritis Impact-Measurement Scales implies that an improvement in cardiovascular fitness results from increased physical activity associated with decreased pain in the joint. Similar improvement in muscle strength and endurance may be expected with increased physical activity. Long et al.15 reported that gait velocity gradually increased to normal during the two years after total hip arthroplasty, a finding that is consistent with our observation that a period of two years is necessary to achieve a significant improvement in cardiovascular fitness after total knee arthroplasty. Osteoarthrosis and inflammatory arthritis of the knee are commonly treated medical conditions. As pain gradually worsens, however, activity becomes more limited, which is associated with cardiovascular deconditioning26. Therefore, it is not surprising that the manifestations of coronary heart disease may occur more frequently in patients who have osteoarthrosis compared with those who do not25. The association between osteoarthrosis and cardiovascular deconditioning has been previously recognized2,11,19,25,30. However, there is no agreement among physicians regarding the best form of regular exercise that should be recommended for patients who have osteoarthrosis as weight-bearing activity may increase the symptoms in the joint. After joint replacement, a patient should avoid impact loads as they may compromise the longevity of the implant12, but other activities including walking, swimming, riding a bicycle, and playing golf are not contraindicated. Our results indicate that resumption of routine walking activities after total knee arthroplasty improves cardiovascular fitness. Better fitness is associated with a decreased risk for the manifestations of coronary heart disease8,21,23,28. Therefore, total knee arthroplasty may be a therapeutic measure in the treatment of coronary heart disease for patients who have osteoarthrosis that severely impairs physical activity because of pain in the knee. As our findings are based on a relatively small number of patients, the results should be considered preliminary.
*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 the Stephen C. Clark Foundation, the National Institutes of Health, and the E. Donnall Thomas Research Program.
  CiteULike  Connotea  Del.icio.us  Facebook  Technorati  Twitter What's this?
This article has been cited by other articles:
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Top
Abstract
Introduction
| home | CME | help | feedback | subscriptions | archive | site index |
|
Stanford University Libraries' HighWire Press (TM) assists in the publication of JBJS Online. |