PT Classroom - The Use of Continuous Passive Motion After Total Knee Arthroplasty ׀ by Chai Rasavong, MPT, MBA

A continuous passive motion (CPM) machine is generally utilized as soon as possible postoperatively for aiding recovery after a total knee arthroplasty (TKA). The function of the CPM machine is to move the knee joint slowly through a controlled range of motion (ROM) to prevent joint stiffness and the development of scar tissue. It has been estimated by the president of an American company that makes and sells CPM devices that, as of 2002, CPM was being used in 17,000 hospitals in 77 countries and that about 7 million patients had been treated using CPM (1). Although the CPM machine may be a commonly prescribed treatment method, the effectiveness of its use remains conflicting.

In a review by Brosseau et al. (2), they conducted a meta-analysis of 14 studies to examine the effectiveness of CPM following total knee arthroplasty. Their study concluded that CPM combined with conventional physical therapy increased the active knee flexion of patients who had underwent a TKA by only 4° (and only at 2 weeks of follow up) compared to physical therapy alone. They also found through their meta-analysis that the use of the CPM machine decreased the length of stay for patients by 0.69 days and reduced the need for manipulation following TKA. In the face of these findings the authors did question the clinical significance of an additional 4° of knee flexion and cautioned on the interpretation of the length of stay data as many of the studies are historic in the terms of contemporary lengths of stay following TKA (3).

In a study by McInnes et al. (4) they evaluated the efficacy of CPM in postoperative management of patients undergoing TKA by conducting a randomized controlled single blind trial of 93 patients who participated in CPM plus standardized rehabilitation vs. standardized rehabilitation alone. Their study found that CPM patients achieved earlier motion and had 7° more active flexion on post op day 7 than those patients who didn’t receive CPM. However, by 6 weeks post op, the range of motion in the two groups were virtually identical.

In another study by Denis et al. (5), they conducted a randomized clinical trial to compare the effectiveness of 3 in-hospital rehabilitation programs for ROM in knee flexion & extension, functional ability and length of stay after undergoing a TKA. Eighty-two subjects were randomly assigned to 1 of 3 groups immediately after a TKA: a control group who received conventional physical therapy only; a second group which received conventional physical therapy and 35 minutes of CPM applications daily; and a third group which received conventional physical therapy and 2 hours of CPM applications daily. The results of their study revealed that adding CPM applications to conventional physical therapy interventions after TKA surgery didn’t favor increase knee ROM, functional ability or length of stay.

From a review of these studies we can conclude that no one study has been able to clearly demonstrate any long term benefit from the use of the CPM machine after TKA surgery. Besides the psychological benefits for a patient by using a CPM machine, conventional physical therapy services along with a home exercise program should be adequate for preventing joint stiffness and the development of scar tissue in most cases.

Last revised: January 11, 2010
by Chai Rasavong, MPT, MBA