A prospective, controlled, randomized trial of continuous passive motion
and immobilization after knee arthroplasty revealed that continuous passive
motion significantly improved early and late flexion of the knee, reduced
the duration of stay in the hospital, and did not increase the incidence of
superficial infection or problems with wound-healing. Flexion of the knee
beyond 40 degrees progressively diminished viability of the edges of the
wound, particularly the lateral edge. On the basis of these results, a
protocol for continuous passive motion was designed to minimize the
detrimental effects on viability of the wound.