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© 1997 The Journal of Bone and Joint Surgery, Inc. The Effect of Active Movement of the Foot on Venous Blood Flow after Total Hip Replacement*  , BELFAST, NORTHERN IRELANDInvestigation performed at the Department of Orthopaedic Surgery, Musgrave Park Hospital, Belfast
Surgeons often encourage patients to move their feet in an attempt to prevent venous stasis, but there is little evidence that this measure is beneficial. We investigated the effect of active movement of one foot on the venous blood flow four days after total hip replacement. The actual venous outflow at rest was measured with use of venous occlusion strain-gauge plethysmography in thirty-eight patients. The patients were randomly allocated to the control group (eighteen patients) or the exercise group (twenty patients). A baseline measurement was followed by a one-minute period of rest (control group) or of maximum plantar flexion and dorsiflexion of the foot, ankle, and toes at a rate of thirty cycles per minute (exercise group). The venous outflow was measured again at two, seven, twelve, and thirty minutes in both groups. Movement of the foot for one minute produced a significant and sustained increase (p < 0.002) in the venous outflow (mean maximum increase, 22 per cent). The value remained greater than the baseline level for thirty minutes (mean increase, 6.5 per cent) (p < 0.2). The increase was gradual, reaching a maximum twelve minutes after the completion of exercise. Our results confirm the beneficial hemodynamic effects of active movement of the foot in the postoperative period and suggest that patients should move the feet and ankles postoperatively as part of a prophylactic regimen directed at decreasing the risk of venous thrombosis.
The association of postoperative deep-vein thrombosis with venous stasis was originally proposed by Virchow in 1859 and has been confirmed recently in patients who have had a total hip replacement16. Medical students are taught to encourage patients to move the feet and toes while they are in bed, and surgeons believe that active movement of the feet in the postoperative period is beneficial. However, there is little published evidence to support the use of active exercise for the prevention of venous thrombosis. To the best of our knowledge, there are no reports of the effects of active exercise on the venous system in the orthopaedic literature. In a single controlled, randomized study of 150 patients, the use of continuous passive motion was found to have no effect on the prevalence of deep-vein thrombosis after total knee arthroplasty15. Sharrock et al. cited unpublished data that suggested that blood flow in the femoral veins could be increased by more than 30 per cent with active movement of the foot after total hip replacement; however, the details of that study were not reported. Historically, the use of active motion and early walking has been supported by the results of uncontrolled studies of patients who had a general operative procedure14,17. Flanc et al. recommended vigorous plantar flexion of the ankle against resistance for five minutes every hour, but a benefit with regard to the prevention of deep-vein thrombosis could not be demonstrated clearly. Tsapogas et al., in a venographically controlled, randomized study, compared a combination of treatment (compression stockings, elevation of the limb, and active and passive movement) with no prophylactic measures. The combined treatment was associated with a reduction in the prevalence of thrombosis, but it is difficult to determine whether the benefit could be attributed to the active exercise. Nicolaides et al. as well as Bird performed physiological assessments of the effect of exercise on blood flow. Nicolaides et al. studied five patients who had not had operative treatment and found that radioisotope clearance from the calf veins was accelerated by active plantar flexion of the foot; however, Bird, who evaluated one patient after an operation, did not find improved blood flow after either routine physiotherapy or strenuous exercise of the ankle. Unfortunately, the exercise protocol was not defined. The present study was designed to investigate the hemodynamic effects of active movements of the ankle and the foot on the venous system in the early postoperative period after a major operation on a lower limb.
Patients who had been admitted for primary total hip replacement for osteoarthrosis were recruited for the study after they had given informed consent. The details of the study had been discussed with the chairman of the local ethical committee, who decided that approval was not needed for the investigation. There were no exclusion criteria during the recruitment process. All patients had insertion of a Charnley prosthesis with cement, through a posterior approach, with use of spinal anesthesia. Thromboprophylaxis consisted of intravenous administration of dextran 70 during the operation and on the first two postoperative days. Dextran was not administered on the day of testing. Surgeons were free to add any other prophylactic agent after the study had been completed. A standardized policy for mobilization was followed: patients sat in a chair on the first postoperative day and walked with partial weight-bearing on the second day. No mechanical devices were used for prophylaxis before the measurement of blood flow. The actual venous outflow was measured with venous occlusion strain-gauge plethysmography. This method has been shown to provide an objective and repeatable assessment of the ability of the venous system of the limb to empty blood9,11,19. The effect of movement of the foot on blood flow was measured in the involved limb on the fourth postoperative day; a previous study16 had demonstrated that this is the time of maximum venous stasis after total hip arthroplasty. The patients were allocated randomly to the exercise group or the control group with use of a method involving concealed cards. Randomization and measurements of blood flow were carried out by a research nurse who was not involved in the design of the study or in the analysis of the results. Plethysmography was performed on the orthopaedic ward, with the patient lying in bed. Testing was done after an equilibration period of at least thirty minutes of rest to eliminate the effects, if any, of standing, sitting, or walking on the measurement of blood flow3,4. An initial baseline plethysmograph was obtained with use of a standardized protocol, as previously described16. The patients in the control group remained at rest after the baseline measurement. The patients in the exercise group followed a controlled protocol that consisted of maximum active plantar flexion and dorsiflexion of the ankle, foot, and toes at a rate of thirty cycles per minute for one minute. The patients were verbally encouraged to maintain the full range of motion, and the rhythm was kept with the aid of a ticking clock. Plethysmography then was repeated at two, seven, twelve, and thirty minutes after the completion of exercise. The same measurements were made in the control group at two, seven, twelve, and thirty minutes after a one-minute period of rest. The venous outflow was calculated from the plethysmographic traces with use of the method of Cramer et al. and was expressed as milliliters of blood per 100 milliliters of tissue per minute (flow per unit volume of tissue). The values before and after exercise or rest were compared with use of a two-tailed paired t test, and an unpaired t test was used to compare the two groups. A value of p <0.05 was regarded as significant.
Thirty-eight patients were recruited and randomized; twenty were allocated to the exercise group and eighteen, to the control group. There were thirteen men and twenty-five women, and the mean age was 70.6 years (range, sixty to eighty-two years). There was no difference in the age range or the gender distribution between the two groups. There were no complications related to any of the 190 measurements that were recorded, and all of the patients could comply easily with the exercise protocol. No patient had symptoms or signs suggestive of deep-vein thrombosis, and all were allowed out of bed normally. There was no significant difference (p > 0.7) between the two groups with regard to the baseline value (the level determined at rest); the venous outflow was 29.8 milliliters per 100 milliliters per minute in the exercise group compared with 30.2 milliliters per 100 milliliters per minute in the control group. The venous outflow in the control group remained close to the baseline level throughout the period of testing, and there was no significant difference between any of the measurements. In the exercise group, an increase in the venous outflow was detectable two minutes after exercise and the value became significantly greater (p < 0.04) than the baseline value at seven minutes. The outflow further increased at twelve minutes (p <0.002), but it returned to a level near the baseline value thirty minutes after the completion of exercise (p < 0.2) (Fig. 1).
The mean maximum venous outflow in the exercise group was 22 per cent greater than the baseline value (p < 0.002). However, in four patients in this group, the maximum outflow was more than 50 per cent greater than the baseline value and the venous outflow at thirty minutes was significantly greater (p < 0.009) than the baseline level. All of the patients in the exercise group had some increase (range, 7 to 53 per cent) in the blood flow compared with the baseline level (Fig. 2).
Prevention of venous stasis in patients who have had a major operative procedure on a lower limb has been widely recommended in recent consensus and review papers13,26. Mechanical devices employing static compression, pneumatic compression of the calf, or venous pumping in the foot have been shown to be effective for prophylaxis against deep-vein thrombosis in clinical trials involving operations on the hip. Thus, it is surprising that so little has been published on the effects of active motion on venous hemodynamics or thrombogenesis. An increase in blood flow after exercise has been observed in physiological experiments since the classic studies by Gaskell. The mechanism controlling this increase is controversial, but it has been proposed that active contractions of skeletal muscle cause transient occlusion of arterial perfusion and this, together with the increased metabolic requirements of exercising muscle, produces a local increase in anaerobic metabolites and a neurogenic response1,2,10,11,20,22. The need to remove metabolites is the principal stimulus for hyperemia, and the degree and duration of increased blood flow have been correlated with the frequency and force of muscle activity20,24. It is difficult to determine the relevance of these physiological data to patients in the postoperative period. Much of the data have been derived from experiments on animals and from studies involving young healthy volunteers. The vascular response in older patients is known to be very different7,12,25, and the influence of an operation on normal venous homeostasis has not been investigated, to our knowledge. The duration and frequency of exercise in our protocol had been determined in a pilot study. Investigators who have studied normal volunteers have advocated longer exercise at a maximum level to produce substantial hyperemia. Stick et al. showed that the venous response to exercise depends on the degree and velocity of muscle contraction. Our group of patients could not perform very frequent contractions or exercises for longer than two minutes because of fatigue or discomfort in the thigh around the operative wound. A short period of tolerable exercise produced significant improvement (p < 0.002) in blood flow, and the patients complied well with this protocol. This compromise may be beneficial, as it was recently shown that maximum exercise may cause activation of the coagulation system21. We demonstrated that substantial hyperemia (a mean 22 per cent increase in the venous outflow) was produced by exercise in patients who had had total hip replacement, but the increase developed over several minutes. This suggests that it is difficult to increase the arterial inflow in response to exercise in older patients. In addition, hyperemia persisted for as long as thirty minutes, possibly because of a greater need, or a reduced ability, to wash out metabolites. In our previous study16, we proposed a mechanism of active venoconstriction in venous stasis after total hip replacement. An increase in vascular tone after an operation may contribute to impaired hyperemia after exercise in patients who have had a total hip replacement. The present study demonstrates improvement in venous hemodynamics but provides no information on the prophylactic effect of exercise on venous thrombogenesis. That effect can be determined only through clinical trials in which active movement is incorporated. If the method is to be beneficial, it must be performed often throughout the day. On the basis of our results, it is reasonable for surgeons to continue to advise patients to move the feet and the toes regularly as part of a prophylactic regimen after an operation on the hip.
NOTE: The authors thank Thelma Pedlow for help with the collection of the data, and all of the orthopaedic surgeons at Musgrave Park Hospital, who allowed us access to their patients for this 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. No funds were received in support of this study.
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