Continuous passive motion after total knee arthroplasty: a prospective study

Continuous passive motion (CPM) has been shown to increase significantly the amount of knee flexion for patients with total knee arthroplasty in the acute care hospital. Whether there is any additional benefit to using CPM for these patients who are transferred to a rehabilitation hospital is not known. There have been no prospective, randomized, controlled studies in this area.

Fifty-one such patients on an inpatient rehabilitation service were randomly assigned to two groups. Group 1 (n = 23) received CPM for 5 consecutive hours per day plus physical therapy, whereas group 2 (n = 28) received only physical therapy. Knee flexion was measured by a blinded physical therapist on admission, on the third and seventh days of hospitalization, and at the time of discharge.

The results indicated no significant difference in passive range of motion between group 1 and group 2. Patients in group 1 achieved an average increase in passive range of motion of 16 degrees, whereas those in group 2 achieved an average of 19 degrees (P = 0.33).

Although power analysis indicated the need for differences in results for 32 patients per group to achieve significance, the difference between the two groups suggested neither statistical nor clinical significance. We concluded that the use of CPM in the rehabilitation hospital is likely of no added benefit to patients admitted after single total-knee replacement.