CPM, also called continuous passive motion, is a device that is used to gently flex and extend the knee joint. The CPM machine can be used after surgery to allow the knee joint to slowly move. The initial thought was that CPM would improve motion following knee replacement surgery, as well as other knee procedures, and eliminate the problem of stiffness. By placing the knee in this device soon after surgery, scar tissue would not develop, and the problem of stiffness would not be a concern.
Several recent studies have investigated the use of the CPM following knee replacement surgery
and ACL reconstruction surgery
. In nearly every study the results are essentially the same: there is some benefit in the first days and weeks following surgery, but there is no difference in knee motion after about six weeks. It does not seem to matter if the CPM is used, ultimately, the results are the same.
Knee surgery has come a long way in the past fifty years. However, orthopedic surgeons are always looking into ways to improve their results. One persistent problem following joint surgery is stiffness of the joint. Knees are especially problematic, because in order to resume our normal activities, we depend on excellent knee motion. The continuous passive motion, or CPM, was developed in an effort to begin motion as soon as possible following surgery, and hopefully alleviate the problem of post-operative stiffness.