INTRODUCTION

In 1960, Salter and Field¹⁶ showed that immobilization of a rabbit knee joint under continuous compression, provided by either a compression device or forced position, resulted in pressure necrosis of cartilage. In 1965, Salter and colleagues¹⁷ reported the deleterious effects of immobilization on the articular cartilage of rabbit knee joints and the resultant lesion that they termed obliterative degeneration of articular cartilage. Salter¹⁵ believed that, “The relative place of rest and of motion is considerably less controversial on the basis of experimental investigation than on the basis of clinical empiricism.” He reasoned that because immobilization is obviously unhealthy for joints, and if intermittent movement is healthier for both normal and injured joints, then perhaps continuous motion would be even better. Because of the fatigability of skeletal muscle, and because a patient could not be expected to move his or her own joint constantly, he concluded that for motion to be continuous, it would also have to be passive. Thus, he invented the concept of continuous passive motion, which has come to be known as simply CPM. Salter also believed that CPM would have an added advantage; namely, that if the movement was reasonably slow, it should be possible to apply it immediately after injury or operation without causing the patient undue pain.

FOUR STAGES OF ELBOW STIFFNESS

Because the elbow is so prone to post-traumatic and postsurgical stiffness, CPM should be especially useful in maintaining motion and preventing such stiffness. The rationale for this is much clearer if one understands the stages of stiffness, of which there are four.

The first stage, occurring within minutes to hours following surgery or trauma, is caused by bleeding. The second stage, which occurs during the next few hours and days is very similar but progresses more slowly. It is due to edema. Both bleeding and edema result in swelling of the periarticular tissues, thereby diminishing their compliance. The immediate effect is to limit joint motion and make it more painful and, therefore, less acceptable to the patient. Thus, stiffness in these first two stages is avoided by preventing swelling. This can be accomplished by ensuring that the joint is moved through its entire range of motion right from the start, rather than only a portion of its range. CPM is required for this purpose.

The third stage is characterized by deposition of extracellular matrix and the formation of granulation tissue commencing near the end of the first week. It continues for days or weeks. The stiffness is still soft but may require the use of splints to regain motion. The fourth stage commencing after about a month results from fibrosis and is often amenable only to splinting or surgical treatment.

PRINCIPLES OF USE

Based on an understanding of how stiffness develops, the principles of use of CPM are readily understandable. Until motion is started, it is preferable to elevate the limb with the elbow in full extension and wrapped in a Jones dressing to minimize swelling. It should not be a compressive wrap because of the risk of losing circulation. A drain is usually useful to prevent accumulation of blood. Before starting CPM, all circumferential wrapping (e.g., Jones, cling) should be removed and replaced with a single elastic sleeve. Failure to do this may cause soft tissue injuries due to shear stresses.

Once CPM is started, it is optimal that the full potential range of motion of that specific joint be used (Fig. 10-1A and B). Essentially, the tissues are being squeezed alternately in flexion and extension. CPM causes a sinusoidal oscillation in hydraulic pressure within and around the joint.^2,9 This not only rids them of excess blood and fluid but prevents further edema from accumulating.⁸ In the first 24 hours, swelling can develop in minutes (due to bleeding), so CPM should be virtually continuous. This has a beneficial effect on healing soft tissues similar to that seen with compressive therapy after eccentric muscle injury.⁶ Bathroom privileges are allowed, and the patient is instructed to come out of the CPM device once every hour for 5 minutes. This safety precaution is to reduce the risk of a pressure or stretch related nerve palsy. As the number of days following surgery increases, the amount of time required for swelling to develop increases also, so that longer periods out of the machine are permitted.

FIGURE 10-1 A to C, The range of motion on continuous passive motion should be full. This permits the tissues to be squeezed alternately in flexion and extension. Analgesia is accomplished with an indwelling catheter for continuous brachial plexus block anesthesia using bupivacaine, a long-acting local anesthetic.

CPM requires close supervision by someone skilled with its use, so it is mandatory that the patient and family are involved and educated from the beginning regarding the principles of use and how to monitor the limb. Frequent checking and slight adjustments of position prevent pressure-related problems. The arm tends to slip out of the machine, so it must frequently be pulled back into it. Nurses do not always have sufficient time, or sometimes the experience, to look after these needs. The patients and their families develop a keen sense of responsibility very quickly and become an invaluable asset. A preoperative instructional video is useful to educate them and should be watched again postoperatively.

The CPM should be used long enough to get the patient through the period during which he or she will be unable to accomplish the full range of motion by himself or herself. This can be several days to a month. For most contracture releases, it tends to be used for four weeks.

PAIN CONTROL

Such use of CPM immediately raises questions and concerns regarding uncontrollable pain. Pain control in these patients requires that we depart from traditional teaching. Rather than adjusting the motion according to the level of pain, the analgesia is adjusted instead. This is no different from the principles of anesthesia for surgery. Some patients have more pain than others, and appropriate modifications need to be made for them.

We favor the use of an indwelling catheter for continuous brachial plexus block anesthesia (see Fig. 10-1C).^13–17 This permits a range from analgesia to anesthesia by varying the dose of bupivacaine, a long-acting local anesthetic. The initial bolus dose may be sufficient to cause a complete or near-complete motor and sensory block. Motor blockade requires splinting of the wrist to protect it. Moderate or complete anesthesia, as opposed to analgesia with minimal anesthesia, requires careful attention to the status of the limb overall, because the patient’s protective pain response is no longer present. Insidious development of a nerve palsy during CPM may be less likely to go unnoticed if some motor and sensory function are still present in each nerve during CPM.

The catheter is left in place for 3 days in hospital, then removed. At that time, the patient is usually able to maintain the same range of motion with either no or only oral analgesics. The goal is to have the patient leave the hospital capable of moving the elbow from about 10 to 140 degrees of motion actively. Of course, full motion is preferred.

A patient-controlled analgesia pump with mor-phine has also been used effectively if a brachial plexus block is contraindicated, unsuccessful, or not available.

ADVANTAGES

There are a number of advantages to the use of CPM. Most surgeons are aware from the total knee experience that analgesic consumption is diminished because the patients are more comfortable (although not always during the first day or two). Swelling is diminished.

Although most experience with CPM has been in the knees, several studies have documented the efficacy of CPM for the elbow.^1,5,11,12 In two separate studies, postoperative CPM was found to improve elbow motion following open reduction internal fixation (ORIF) of distal humeral fractures in children and adolescents.^11,12 CPM has been also documented to be effective in assisting with restoration of elbow motion after surgical release¹ or resection of heterotopic ossification.⁵

My personal experience using CPM in strict accordance with the principles just outlined has convinced me that motion is obtained faster and more completely than that obtained without the use of CPM, despite the studies that failed to show such a benefit in the knee (Fig. 10-2A and B).^7,8,18,19 This can be explained on the basis of how CPM has been routinely used. Typical protocols involve starting with a small range of motion tolerated by the patient, for example 30 degrees, and gradually increasing the range each day. This pattern of use is not in compliance with the essential principles of CPM. What such a protocol does is to increase swelling and bleeding due to constant tissue irritation.

FIGURE 10-2 Typical range of motion seen 3 weeks postoperatively (A) and 1 year postoperatively (B) following a distraction interposition arthroplasty treated postoperatively using continuous passive motion.

The most astonishing benefit of CPM, however, is how rapidly the patient is capable of pain-free and relatively full function and, therefore, return to work and sport.

COMPLICATIONS

In using CPM for the elbow, I have become aware of the protocol for complications. Bleeding is increased but rarely sufficiently to require a transfusion, although some patients have been taken back to the operating room for evacuation of a hematoma under such circumstances. Those elbows were treated by being placed back into a well-padded Jones dressing with an anterior plaster slab holding the elbow in extension, then elevating the arm for 2 to 4 days. It is clear to me that in certain settings, CPM can increase the risk of soft tissue and wound healing complications. Hematomas and seromas, as just mentioned, are more likely if CPM is used after having raised a skin flap as part of the exposure. When large skin flaps have been raised and the extent of deep dissection has been extensive, CPM may cause shearing of the soft tissues that is not able to be tolerated. This leads to dark discoloration of the skin, possibly full thickness necrosis, blistering and/or persistent weeping through the wound. If the wound is not closed very securely (subcuticular stitches are insufficient), it may dehisce. I have changed my use of skin incisions and CPM in these types of cases for these reasons. In such circumstances I prefer medial/lateral incisions with no skin flaps rather than a posterior incision. If I am concerned about soft tissues, I delay the use of CPM for 2 to 4 days until I see how the tissues respond to the surgery itself. Despite these concerns, no patients have lost a flap, although a few have had areas of necrosis that healed by secondary intention without further surgery. One patient almost fell out of bed from lying so close to the edge while using the machine.

A word of caution is required. No circumferential wrapping (e.g., cling) should be left on the elbow once the CPM is started. A single elastic tube grip sleeve is best.

I do not generally use CPM in the presence of ligament injuries or potential joint instability because it is not possible to keep the elbow perfectly aligned with the axis of rotation of the machine. Malalignment would stress the ligaments and bony stabilizers of the joint.

Neurologic complications of CPM are well recognized for the leg. With the elbow, CPM can permit pressure-induced palsies, which can be prevented as discussed earlier. Delayed-onset ulnar neuropathy is a risk after contracture release. It appears to be due to compression by the cubital tunnel retinaculum and can largely be prevented by prophylactic nerve decompression. Obviously, any nerve can develop a palsy from stretch as well.

INDICATIONS AND CONTRAINDICATIONS

CPM is indicated to prevent stiffness and to retain motion obtained at the time of surgery, particularly following contracture release, synovectomy, and excision of heterotopic ossification. I do not generally use it following the replacement of arthritic joints that were stiff preoperatively because of concern about soft tissue complications that would be serious overlying a prosthesis. It is relatively contraindicated if the soft tissue constraints (ligaments) are insufficient, if fixation of fractures has not been rigid, or if the elbow is unstable.

HOME USE

I believe that the use of CPM at home is as important as, or perhaps even more than, its use in the hospital. The home rental market for CPM machines is being served by at least two domestic companies at the time of this writing, so home use of CPM is practical. The typical requirement is in the range of 4 weeks for an elbow that has been stiff before surgery, and 1 to 2 weeks for elbows requiring assistance to prevent stiffness from developing.