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.