CPM (continuous passive motion) protocol following surgical intervention

Stiffness following surgery or injury to a joint develops as a progression of four stages: bleeding, edema, granulation tissue, and fibrosis. Continuous passive motion (CPM) properly applied during the first two stages of stiffness acts to pump blood and edema fluid away from the joint and periarticular tissues. This allows maintenance of normal periarticular soft tissue compliance. CPM is thus effective in preventing the development of stiffness if full motion is applied immediately following surgery and continued until swelling that limits the full motion of the joint no longer develops. This concept has been applied successfully to elbow rehabilitation, and explains the controversy surrounding CPM following knee arthroplasty.

INTRODUCTION

  Von Riemke, in his presidential address to the Danish Surgical Society in 1926, stated that, "All joint affections...should be moved. Movement should begin on the first day, should be very slow, and as much as possible it should be continuous." Salter, who invented the concept of continuous passive motion, which has come to be known as simply "CPM," derived this concept on the basis of a series of experimental investigations and well thought-out rationale. Salter and Field (1) showed in 1960 that immobilization of a rabbit knee joint under continuous compression, provided by either a compression device or forced position, resulted in pressure necrosis of the cartilage. 

In 1965, Salter et al. (2) reported deleterious effects of immobilization on the articular cartilage of rabbit knee joints and the resultant lesion that they termed "obliterative degeneration of articular cartilage." Salter (3) 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. He 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. This idea was based on the gate-control theory of pain by Melzack and Wall (4,5), that with competing afferent sensory stimulation, painful stimuli would be inhibited. The concepts, tested in patients since 1978, have proven to be feasible

DISCUSSION

Pathophysiology of Joint Stiffness
The Four Stages of Stiffness:

1. Bleeding
2. Edema
3. Granulation Tissue
4. Fibrosis

Stage 1: Bleeding
  The first stage, occurring within minutes to hours following articular surgery or trauma, is caused by bleeding, which results in distension of the joint capsule and swelling of the periarticular tissues. Depending on the individual joint, the capsule achieves a maximum potential volume at a certain joint angle. In the knee, the maximum capacity of the joint capsule has been found to occur at approximately 35° of flexion (23-26); in the elbow, it occurs at 80° of flexion (27). Any attempt to flex or extend a joint beyond its position of maximum capacity, when the joint and/or periarticular tissues are markedly swollen, creates extremely high hydrostatic pressures within the joint and periarticular tissues. Associated with these high pressures are severe pain and a marked increase in resistance to motion. Immediately following injury or surgery to the joint, the natural tendency is to hold the joint in the position of maximum articular volume to minimize painful stretching of the joint capsule and the pressure of the intra-articular hematoma.

Stage 2: Edema
  The second stage of stiffness, which occurs during the next few hours or days, is very similar but progresses less rapidly. It is due to edema, caused by inflammatory mediators that are released by platelets and dead and injured cells. These mediators cause nearby blood vessels to dilate and leak plasma, resulting in swelling of the periarticular tissues, thereby diminishing their compliance. With swollen and less compliant tissues surrounding it, the joint becomes physically more difficult to move and movement becomes more painful (24,27). Up to this point, stiffness and loss of periarticular tissue compliance are simply due to the accumulation of fluid. In the next two stages, fluid is replaced by extracellular matrix deposition, marking a significant transition.

Stage 3: Granulation Tissue
  The third stage consists of the formation of granulation tissue. This occurs during the first few days or weeks following trauma or surgery. Granulation tissue is a highly vascularized, loosely organized tissue with material properties somewhere between a highly organized blood clot and loose areolar fibrous tissue. As this granulation tissue appears within and surrounding the joint, the stiffness previously due to fluid accumulation becomes increasingly due to the deposition of a solid extracellular matrix.

Stage 4: Fibrosis
  The fourth stage of stiffness represents fibrosis. During this stage, the granulation tissue matures, forming dense, rigid scar tissue. This scar tissue has a high concentration of collagen type I fibers in its extracellular matrix.

Evolution of Joint Stiffness
  To understand how a joint ends up permanently stiff, it is necessary to understand how the stiffness evolves, and how one stage ushers in the next. Let us consider the example of a total knee arthroplasty. At the completion of the procedure (with the patient still anesthetized), when the wound has been closed, the knee has a certain range of motion. If one were to bring the patient back to the operating room from the recovery room 2 hours later and reexamine the patient's knee under general anesthesia, it would not move through the full arc of motion found intraoperatively. This is because the accumulating blood in and around the knee causes distention and loss of compliance of the periarticular tissues. However, if this blood were forced out of the periarticular region (or better still, not permitted to accumulate), mobility of the knee would immediately be restored.

  One to 2 days later, if one were to examine the patient's knee again under general anesthesia, it would certainly not move through a full arc of motion based on current practices of rehabilitation following total knee arthroplasty. This loss of motion is due to accumulation of fluid, representing the second stage of stiffness, edema. It is still possible to eliminate this fluid from the periarticular tissues, but that requires sustained "milking" of the fluid away from the region of the joint.

  Several days later, the knee definitely has a feel of stiffness that cannot be overcome by milking the fluid out of the region. In this third stage of granulation tissue deposition, extracellular matrix is being deposited in the tissues around the knee joint, causing them to thicken and greatly lose their compliance. A knee at this stage is still amenable to "manipulation" under anesthesia, but a degree of force is required to overcome the blocked motion. Several weeks to months later, when fibrosis is occurring during the fourth stage of stiffness, the extracellular matrix and granulation tissue are being replaced by dense, collagenous scar tissue. This provides great resistance to mobility, and the loss of motion cannot be overcome, even with manipulation

Principles of CPM Application
  Using this theory, the role of CPM in preventing joint stiffness can be clarified. In the first few days following injury or surgery, CPM is useful primarily to minimize joint hemarthrosis and periarticular edema; CPM has been found to increase the clearance of a hemarthrosis from a rabbit knee (28). In the presence of a joint effusion, movement of the knee away from the position of maximum volume and compliance causes an increase in intra-articular pressure. The greater the effusion, the greater the pressure generated at a certain degree of joint flexion (23-27). CPM causes a sinusoidal oscillation in intra-articular pressure (29), as shown in Figure 1 (30). This accelerates the clearance of a hemarthrosis (Figure 2). The enhanced clearance of blood from within the joint (Figure 3) as well as the clearance of blood from the periarticular tissues (Figure 4) due to CPM has been documented and quantified by tracking radiolabeled erythrocytes.

Figure 1. An actual tracing of the intra-articular pressure in one knee during CPM reveals that, with 2 ml of fluid in the joint, the pressure oscillates in a regular sinusoidal fashion. This results in a "pumping effect" which is responsible for clearing blood and edema fluid from the joint and periarticular tissues. (Reproduced with permission from O'Driscoll et al. J Rheumatol. 10:360-3, 1983.)

Figure 2. Alternate flexion and extension of the joint by CPM raises and lowers the hydrostatic pressure in the joint and periarticular tissues resulting in a "pumping effect" that forces fluid out of the joint and periarticular tissues.

Figure 3. Effect of CPM on clearance of a hemarthrosis. CPM rapidly accelerates the clearance of blood from the joint in the periarticular soft tissues, as seen in these comparison photographs at 48 hours and 7 days following injection of 2 cc of blood into both knees of a series of rabbits. The rabbits were treated by immobilizing one knee in a cast and moving the other knee on a CPM machine immediately following surgery and then continuously for 7 days. At 48 hours, the knee that had been immobilized in a cast (left) was still grossly bloody, whereas the opposite knee (right) treated by CPM was almost free of blood. At 7 days, the cast knee contained free blood in the joint while the CPM knee from the same rabbit was clear. In contrast to the immobilized knees, most of which contained small amounts of blood in the synovium at 7 days, all of the CPM knees appeared normal. Proper use of CPM, as described in this paper, immediately raises questions and concerns regarding uncontrollable pain. Achieving satisfactory 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 than the principles of anesthesia for surgery. Some patients have more pain than others, and appropriate modifications need to be made for them.   There are essentially three options for pain control: 1) narcotic medication, either by injection or by continuous infusion using a PCA (patient controlled analgesia) pump; 2) local anesthetic by continuous infusion with an indwelling catheter and infusion pump; or 3) regional anesthetic, by brachial plexus block anesthesia in the upper limb, or nerve blocks or epidural in the lower limb. With upper limb surgery, we favor the use of an indwelling catheter for continuous brachial plexus block anesthesia (31-35). This permits a range from analgesia to anesthesia by varying the dose of bupivacaine, a long-acting local anesthetic. In many cases, the dose initially employed is 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 overall status of the limb, as the patient's protective pain response is no longer present.   The catheter is left in place for 3 days in the hospital, then removed. At that time, the patient is usually able to maintain the same range of motion with either oral analgesics only or none at all. The goal is to have the patient leave the hospital capable of moving the joint through at least 80 percent of its normal motion, actively, without significant pain (Figure 7); of course, more is better. CPM should be used long enough to get the patient through the period during which he or she will be able to accomplish the full range of motion by him or herself. This can be several days to a month. As the home rental market for CPM machines is being served by at least two companies at the time of this writing, home use of CPM is practical. The typical requirement is in the range of 4 weeks for a joint that was stiff before surgery and 1 to 2 weeks for elbows requiring assistance to prevent stiffness from developing. Figure 7.  Active range of motion 3 days following surgery in a patient with rheumatoid arthritis. Preoperatively, this patient had active and passive motion from 50 to 120° of flexion. Surgery consisted of a total synovectomy and capsulectomy. CPM treatment was given immediately postoperatively and continuously for 3 days: full motion was maintained on the machine continuously and the pain controlled with an indwelling axillary catheter for brachial plexus block anesthesia. Active motion at the time of discharge was painless throughout an arc of 10 to 135° of flexion. Final follow-up confirmed maintenance of this arc of motion. CPM Use in the Knee Following Total Knee Arthroplasty   Understanding the theory and principles of proper CPM application in clinical practice, one is in a good position to review and interpret the literature concerning the use of CPM to facilitate rehabilitation following total knee arthroplasty, for which it has been employed since the early 1980s. In one of the earliest studies of CPM in this patient population, Coutts et al. (13,36) compared knees treated with CPM (begun in the recovery room, initially set at 0 to 40° and advancing by 10° per day) with knees immobilized for a period of 3 days postoperatively prior to beginning any motion. The knees treated with CPM were found to have improved motion 1 year postoperatively. In another study, comparing CPM use to 7 days of splinting following total knee replacement, CPM was again found to improve the flexion of the knee at 1-year follow-up by an average of 10° (14). These studies support the notion that early postoperative motion is better than prolonged immobilization following total knee arthroplasty.

Figure 4. Treatment with CPM enhanced the rate of hemarthrosis clearance by more than 100 percent. Values expressed as mean±1 standard error of the mean. (Reproduced with permission from O'Driscoll et al. Clin Orthop 176:305-11, 1983.)