The CPM Challenge

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January/February 2003

By Jeff Yip

Donald A. Chu, PhD, PT, ATC, CSCS, director of Stanford University's Athletic Training and Rehabilitaion Department, uses CPM on injured athlete, Evan Combs.

Continuous passive motion (CPM) devices, pioneered by Canadian orthopedic surgeon and researcher Robert Salter, have been used since the 1980s. Although the aim of CPM, helping to bend a joint, is simple, the advancements made in this area have been significant. Over the years, CPM devices have become lighter and easier to set up and use safely, thanks to utilization of microcircuits and computers, aluminum, and plastics.

CPM is applied to a joint after trauma or surgery to reduce swelling and scar tissue, and to improve range of motion. Using CPM correctly and immediately is critical to avoid arthrofibrosis in joints that are prone to stiffness, such as those in the knee, elbow, and hand.¹

Proper CPM can be cost-effective by reducing the need for physical therapy and joint manipulation under anesthesia, and later rehabilitation or surgical intervention to treat stiffness.¹

The practice has also been controversial. While some practitioners swear by CPM devices, others point to research that shows they do not speed up recovery or increase range of motion.

Still, some physicians prescribe CPM no matter what the studies proclaim because their patients have reported less pain. And CPM machines, some say candidly, are beneficial to healing because the patient believes she or he is actively taking a role in the recovery process.

THE BENEFITS OF CPM

CPM machines are “definitely useful,” says Sandra Fuller, RN, MS, PT, of the Athletic Orthopedics & Knee Center in Houston. “A lot of people who come out of surgery won’t be particularly motivated to do their exercises, because of pain. So we’ll use CPM machines,” she says. Most of these cases involve total knee replacements or more involved shoulder surgeries like rotator cuff repair and acromioplasty, she adds.

Jack Jensen, MD, director of the center, has been a fan ever since he heard a talk by Salter in the late 1970s. “I am so impressed with CPM. Patients say it makes their knees feel so much better,” he says. “As for those with rotator cuff [injuries], it’s slow and awkward moving your shoulder. The CPM machines really help. They’re also cost-effective. Patients don’t have to take the time to go to therapy; they can help themselves. And because a lot of injuries require extensive therapy, CPM can mean a physical therapist can spend more one-on-one time with a patient.”

The key to using CPM effectively, Jensen says, is to begin it immediately after surgery. “If the patient has outpatient surgery, therapy should start that day,” he says. “If it’s an inpatient procedure—like a total knee replacement—it’s the same thing. We also will use it with some ligamentous injuries. We’ll give the patient CPM prior to operating.

“Our rule of thumb is that we like to use [CPM] 6 hours a day. If it’s a knee CPM, I tell people that if they can sleep with a device on at night, let it go all night long.”

In San Francisco, the Stone Clinic is another longtime proponent of CPM. “The main use of CPM for us is to augment our articular cartilage paste graft. So, whenever we do one of these procedures, we place a patient in a CPM,” says Kevin R. Stone, MD, founder of the clinic. “We want to encourage pluripotential cells from the bone marrow to become cartilage, not scar tissue.” The single-surgery procedure is designed to regrow articular cartilage in the knee that has been damaged by trauma or arthritis. The patient’s own cartilage is harvested, mixed into a paste, and transplanted to the defective area. It is all performed arthroscopically.

Postoperatively, the knee is kept non-weight-bearing for 4 weeks. A CPM machine is used 6 hours a day every day during that period. “We also have patients doing pool exercises and riding a stationary bike during that [time],” Stone says.

But CPM is not used when a meniscus transplantation procedure is performed because, he says, “we don’t want to disturb the healing rim of the meniscus.”

CPM IN SPORTS INJURIES

At Stanford University, Palo Alto, Calif, athletes are often put on CPM machines.

“Athletes face a very tough rehabilitation. It’s very painful for the patient,” says Donald A. Chu, PhD, PT, ATC, CSCS, director of the school’s athletic training and rehabilitation department, and former president of the California State Board of Physical Therapy. “Sports medicine demanded aggressive therapy. CPMs were an opportunity for creative thinking and experimentation. Athletes have a greater workload capacity and a higher threshold of pain.”

CPM helps as “the tissues are remodeling,” Chu says. “New tissues need to adapt to lines of stress. The new cells need to be laid down in the proper alignment. If the cells are disorganized, you get things like adhesions and contractions of the tissue.”

With CPM you need to go slowly, Chu says. There should be no voluntary contractions. Patients should not fight it. “CPM is most effective with ligamentous repair such as [anterior cruciate ligament] surgery,” he says. “By employing CPM, you tend to avoid some of the shutdown of the muscle. You can avoid extensor lag and alleviate pain. I’d say that nowadays, ACL patients regain 90% to 95% function.”

Chu warns, however, that patients must achieve maximum range of motion. “It’s easy for people to be using CPM and the gear comes out of alignment. The professional needs to pay careful attention to how it’s fitted. Fit and monitoring are crucial. This can be done either in the doctor’s office or at the patient’s home by the physical therapist.”

CPMs should not be used after surgical procedures that require complete rest, such as rotator cuff repairs, he says. “For those procedures, there has to be no activity. There’s a potential for disrupting the actual healing process.”

ROOM FOR IMPROVEMENT

Durability is one area that CPMs have lagged in, says Vivian Dunlop, PT, inpatient physical therapy director at Memorial Hermann Southwest Hospital in Houston. “We own about 15 [CPM machines],” she says. “At any one time we have a dozen in good working condition. There are usually two or three out for repair.

“The fact that they’re lighter means they probably can’t withstand the wear and tear as much,” she says, adding that the warranties on CPM machines range from 90 days to 1 year. “They last about 5 years.”

Memorial Hermann Southwest Hospital does a lot of total knee replacements, and Dunlop’s team sets up eight to 10 patients a week on CPM machines. “The big difference now is that we’re giving nerve blocks. The patient has a lot less pain,” she says. “We can get them going quicker. We initiate CPM in the recovery room within an hour, or 2 hours at the most.”

The CPM machine operates virtually 24 hours a day while the patient is still in the hospital; their stay can range from 4.5 to 14 days, she says. “The main complaint we get from patients is that the pads are not always comfortable,” she says. “There is a bar that goes under the gluteal area and some patients still feel it through the pads.”

Imagine using your car 6,500 hours a year. At freeway speeds, the odometer would rack up 357,500 miles. This analogy can illustrate the durability challenges faced by CPM machine designers. John Saringer, an engineer and former owner of a CPM equipment vendor, says a busy hospital may operate a CPM machine up to 6,500 hours, or more than 3 million cycles.

“By now, new CPM designs have become quite stable, and are mostly driven by ancillary considerations such as improving reliability, changing a few bells and whistles, and reducing cost,” Saringer says. “By 1990, there was a CPM available to treat every single synovial joint of the body. Some of these, like the machine for the [temporomandibular joint], have been discontinued due to poor demand.”

The important thing to remember when using CPM equipment, he says, is to make sure it is being used correctly. Miko Spurlin, a physical therapist in the Houston area, agrees. He recalls a case where less experienced staff had not padded a CPM machine well and a patient developed a deep open wound.

“The major challenge is education—as it has always been,” says Saringer. “When CPMs are not used properly, the results aren’t that great.”

Jeff Yip is a contributing writer for Rehab Management.

REFERENCE

O’Driscoll SW, Giori NJ. Continuous passive motion (CPM): theory and principles of clinical application. Rehabil Res Dev. 2000;37(2):179-188.

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January/February 2003