CPM Machine after Knee Replacement

cpm
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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 bend. 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.

Latest Developments

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.

Pros

The argument for a CPM is that patients do have an initial increase in motion following surgery that is more rapid than patients who do not use a CPM. Furthermore, patients who use a CPM following knee replacement surgery are less likely to require knee manipulation (where the patient is given general anesthesia, and the knee is forced to bend) than patients who do not use a CPM.

Also, patients often feel a strong desire to be "doing something" to help their recovery. While CPM may not actually alter the result of the surgery, it can give patients a sense that they are doing something to help their recovery, even when resting in bed.

Cons

No one has shown that a CPM makes any difference in the long run. Time and time again, studies show that within 4-6 weeks of knee replacement surgery, patients who use CPM and those that don't have the same range of knee motion. While there may be the psychological effect stated above, there has been no evidence to show that the use of CPM will ultimately improve the outcome of a knee replacement or anterior cruciate ligament reconstruction surgery. That said, there are some specific procedures, such as a release of contracture or adhesions, where a CPM can be an important part of the recovery from knee surgery.  Many surgeons worry that CPM may ultimately slow down recovery by keeping the patient in bed, and not getting more effective active therapy.

Bottom Line: Where It Stands

As stated previously, no one has been able to clearly demonstrate any long-term benefit to the routine use of CPM following a knee replacement or ACL surgery.  As the studies clearly show, patients are likely to be at the same point within six weeks of surgery regardless of the use of a CPM.  More surgeons are recommending against the routine use of CPM and encouraging patients to focus on active therapy efforts of getting up and out of bed.

Sources:

Pope RO, et al. "Continuous passive motion after primary total knee arthroplasty: Does it offer any benefits?" J Bone Joint Surg Br 1997;79:914–917.

Lau SK, Chiu KY "Use of continuous passive motion after total knee arthroplasty" J Arthroplasty 2001;16:336–339.

Bong MR, and Di Cesare PE. "Stiffness After Total Knee Arthroplasty" J. Am. Acad. Ortho. Surg., May/June 2004; 12: 164 - 171.

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