Osteoarthritis, or degenerative arthritis, has been found in the bones of cavemen and even dinosaurs. It is the gradual wearing away of joint cartilage, an irreversible process because the damaged joint responds not by generating new cartilage but by producing bony outgrowths and fibrous, or scar, tissue. Sometimes no cartilage is left at all and the joint becomes too stiff and painful to move. Drugs can't cure the arthritis, and doctors have been reduced to prescribing heating pads and aspirin to dull the pain, symptom of the disease. In the past, surgeons turned to fusing the worn-out joint which stops the pain but also makes it permanently rigid, or, more recently, to replacing the joint with an artificial one. Some arthritis sufferers who haven't been helped medically have tried acupuncture, chiropractic, hypnosis, and even copper jewellery and other home remedies.
Although degenerative arthritis can develop spontaneously, more often it is a response to previous damage. Other joint diseases such as septic arthritis (infected joints) can set it off, as can deformities and injuries. Thus, despite its reputation as one of the agonies of aging, degenerative arthritis can afflict anyone several years after joint damage.
Also, according to Dr. Robert Salter, professor and head of Orthopaedic surgery at U of T and senior Orthopaedic surgeon at the Hospital for Sick Children, degenerative arthritis is sometimes an iatrogenic (doctor-produced) disease. Through his animal research he has shown that when a joint is kept still in a cast or splint for a long time as a form of treatment, several things can go wrong. When a fracture involves a joint surface, prolonged immobilization can cause the fracture in the cartilage to be filled in with scar tissue which later breaks down and leads to arthritis. Or the membrane around the joint can stick to the cartilage like scotch tape in certain areas. Then the joint fluid, the only source of nutrients for cartilage, cannot reach those spots which soon die. Not only injured joints may be subjected to this deterioration but also healthy ones which are often immobilized for several weeks or months when an adjacent bone is fractured.
The aim of Salter's current laboratory research is to prevent degenerative arthritis. Through almost a decade of careful animal studies, he has been proving that, contrary to long-standing medical belief, cartilage can regenerate. The key is motion-in fact, "continuous passive motion," a completely new concept. He has discovered that if joints are moved continuously for at least one week after an operation, defects in cartilage heal with new cartilage and subsequent arthritis is unlikely. Some day, due to Salter's work, the maxim that tissues must be at rest to heal may be as outmoded as blood-letting, and at least some types of degenerative arthritis may be understood as unavoidable, rather than inevitable, consequence of joint damage.
Robert Salter has throughout his career questioned empiricism and dogma. He describes his attitude as what Voltaire called "the spirit of constructive discontent". Today his concepts carry weight, with the credibility of 25 years as an internationally respected researcher, clinician and teacher behind him. A Fellow of the Royal Society of Canada, Companion of the Order of Canada, past president of the Royal College of Physicians and Surgeons of Canada and a winner of numerous honours including a Gairdner International Award for Medical Science, Salter is perhaps best known to Orthopedic colleagues for the operation he designed in 1957 to correct congenital hip dislocations, which was promptly designated (by others) "the Salter operation".
When I arrive at his office at the Hospital for Sick Children for an interview, Salter is still in surgery, so I find a seat outside in the Orthopedic clinic waiting area. Soon a tanned, grey haired figure in OR greens and white coat strides through rapidly, followed by a retinue of young men in white coats-and wearing ties-who are struggling to keep up with him. He flings open the office door; they all go into a huddle inside; the door shuts. A few minutes later it opens gently and the senior of the three secretaries ushers me in.
Salter looks as vigorous standing still as in motion. The eyes behind the professorial glasses appraise me steadily and warmly; the hand that grasps mine is firm. He exudes confidence and authority.
"How," I ask, when we have settled ourselves in his inner office, did you conceive the idea of continuous motion? Isn't it a pretty radical thing to do-to move injured joints continuously?"
"Radical, yes," he repeats, picking up his pipe and beginning the mesmerizing rituals of tapping, filling and drawing, "but innovative and perhaps imaginative too, because it goes against the time honoured concepts of how to manage injured joints."
After his description of current methods of joint treatment, I launch into the topic that is uppermost in my mind: "Are you getting cartilage to regenerate in humans yet?"
"Everybody wants to know that," he replies with an understanding smile.
"They don't want to know about all the research that went on before-just where to push the buttons for clinical applications of the concept."
I laugh with him. He leans back in his swivel chair and pauses effectively. "In answer to your question-yes, we have started applying continuous passive motion to human patients."
Even as a medical student, Salter was, as he puts it, "a mover rather than a rester" and a challenger of the conventional wisdom. Against his team doctor's recommendations, he treated his own three football injuries (torn ligaments in both ankles and a dislocated collarbone) not by plaster casts and rest but by taping them and continuing to play end for the U of T's medicine team. "I simply felt that joints were meant to move," he recalls, "and besides, I wasn't keen on sitting out the rest of the season." Although Salter might not recommend such strenuous activity for his patients today, his own experiences made him curious.
" I began thinking of motion as a spectrum," he continues. "At one end is complete immobilization-a cast. In the middle of the spectrum is intermittent motion-either everyday activity (active motion) or passive movement of joints by a physiotherapist. At the other end of the spectrum is continuous motion." Other researchers had been investigating intermittent motion-in animals by cage activity and in clinical studies by getting patients up and about soon after surgery-and the results were somewhat encouraging. But no one had tried continuous motion. To investigate that extreme, a mechanical device was needed because muscles tire. Hence the concept of "continuous passive motion".
Salter had a hunch that continuous motion would not be painful. His own joint injuries had taught him what arthritis sufferers know: that a joint is stiff and painful in the morning, after it has been at rest for several hours, but the stiffness and pain gradually disappear as it is moved. If, he speculated, a joint could be set in motion immediately after surgery, it might prevent pain and stimulate better healing.
Using a machine for rabbits he had designed and bioengineers at the hospital had built, he first ensured that continuous motion itself would do no harm. He suspended healthy rabbits in slings and simply moved their knees mechanically in slow revolutions (one complete cycle about every 45 seconds) for several weeks. The animals ate, drank and slept as usual, and appeared comfortable. "The younger rabbits continued to gain weight and the adults maintained their weight," says Salter. "That's a good indication of the animal's health, because if a rabbit is sick or uncomfortable it won't eat. We watched the animals very, very closely because we didn't want to cause them harm."
Next, he set out to determine what kind of tissue forms in injured cartilage with different types of treatment. He drilled narrow holes in the cartilage and bone of the right knee joints of 120 rabbits. One-third of the rabbits were then treated by plaster casts (immobilization); one-third were put into cages (intermittent motion); and the remaining third were placed in the machine before their anesthetic had worn off (continuous passive motion). When the rabbits from each group were sacrificed weeks and months later, their joints were examined through a dissecting microscope, light microscope and electron microscope, and new tissues were analyzed biochemically. Subsequent experiments followed the same model of three groups of rabbits; most important for clinical application was the study of joint fractures.
The results of the experiments show a strong correlation between motion and healing. The rabbits that were treated by casts fared the worst. None, when examined six months later, had formed new cartilage. If the fractures had closed at all, they had done so with scar tissue and already there were many signs of arthritis. The rabbits left to hop in their cages were somewhat better off. They also had scar tissue adhesions and signs of arthritis, but 20 percent had formed new cartilage. The rabbits treated by continuous passive motion, however, had no scar adhesions, significantly fewer signs of degenerative arthritis, and 80 percent of them had developed new cartilage.
Salter describes these results with scientific understatement, referring to the new cartilage as "tissue comparable to hyaline cartilage". ("Hyaline" refers to the translucent, glass-like appearance of joint cartilage.) To an observer, however, the new tissue is the real thing. The joints treated by continuous motion are as smooth and shiny as normal joints while those from the other groups are grossly deformed. Through the microscope the new cartilage is indistinguishable from the surrounding cartilage while the other groups show striated scar tissue, deformities and gaps. In histochemical tests, too, the new tissue reacts with the staining patterns characteristic of hyaline cartilage.
Although the biochemical and cellular details of cartilage regeneration are not yet fully understood, Salter has discovered that underlying bone as well as cartilage must be affected if new cartilage is to form. Certain embryonic-like cells located in bone appear to be capable of differentiating into bone, scar tissue, or cartilage, depending on the stimulus. And for some reason motion encourages these cells to form bone where bone should be and cartilage where cartilage should be. Lack of motion, on the other hand, only causes rampant growth of scar tissue.
When Salter was certain of the value of continuous passive motion in the laboratory, he asked Professor David James and John Saringer of the University's Department of Mechanical Engineering to build a device that would provide continuous passive motion for the human knee joint.
The first patient to try the new machine was 16-year-old Michelle who had been born with a condition that caused her knee caps to dislocate easily. In July 1978 she had fallen down a flight of stairs, severely injuring her left knee. Extensive repair work, after which her lower limb was done by a surgeon in her hometown in southern Ontario. However, the knee only seemed to get worse. When Michelle was admitted to Sick Kids, in July 1979, she couldn't support any weight on her left leg. She had not attended school since January and had been on crutches for a year. Her knee was swollen, red and painful and the muscles attached to it had atrophied. She was unable to straighten her leg and could bend her knee only 25 degrees of the normal 150-degree range of motion. Although she was not the ideal patient for what was essentially a clinical trial of a new method of treatment, Salter felt that Michelle needed something more than conventional methods.
He operated, removing the abnormal bony spurs and massive scar adhesions that had built up since the previous operation, and rebuilt her joint using her own tissues. Then, as with the rabbits, before Michelle's anesthetic had worn off, he attached her left foot to the pedal of the machine, which began moving her lightly bandaged knee passively in the slow revolutions that continued night and day for almost three weeks.
When I phoned Michelle, she was eager to talk about her unusual experience at Sick Kids. "I was scared when Dr. Salter told me what he was planning to do," she admits. "I remembered the pain when I woke up from my other operation and I thought, 'Oh wow, this is going to be twice as bad because the knee will be bending too!'."
But what sounded like a torture device actually turned out to be pleasant. "When I woke up, the first thing I saw was my knee bending and I was almost crying because it didn't hurt at all! I never had to ask for needles for pain because I didn't have any. I just couldn't get over it! It felt so good to get it bending again."
Michelle fell asleep easily, lulled by the slow, regular motion; she became so used to the machine that she even had to be weaned off it gradually when it came time to go home. "My life has changed so much since then," Michelle says. "It's just a normal knee now."
Although Salter's face lights up as he recalls the details of Michelle's treatment, he is cautious about making long range claims. But since she still has no pain or stiffness in her knee more than a year after her operation, and since her X-rays are perfectly normal, he admits the chances are good that she, like the many continuous-passive-motion rabbits before her, has developed new hyaline cartilage and that she will continue to have excellent function in her knee for the rest of her life.
Increasingly, patients recovering from other types of surgery are encouraged to move about early but Orthopaedic practice still includes putting joints in casts for several weeks or months. "Heart muscle moves continuously after open heart surgery," Salter observes, "and the incision heals. Same thing with the lung and bowel. The trouble is, it's been done for centuries." Convincing other surgeons to change old habits, Salter realizes, will require good results with many human patients. His clinical applications are just beginning. U of T engineers have built two new machines, one for the elbow and one for the finger, and so far three patients since Michelle have been treated by continuous passive motion.
Meanwhile, Salter's laboratory work is taking new turns within arthritis research. He has just completed studies on septic arthritis and torn ligaments and is confident that patients with these problems can be treated successfully by continuous passive motion. In addition, Salter and his research fellows are currently trying to simulate rheumatoid arthritis in rabbits, in order to study the effect of motion on this condition.
Unlike his rabbits and patients, Salter himself seems to thrive on continuous active motion. Although his research is a high priority and he hopes to devote himself to it full-time when he retires in 10 years, at present he also has teaching responsibilities, administrative duties, frequent visiting professorships and scientific meetings and a demanding clinical practice-and still includes time for his wife Robina, an author, and their five children, David, Nancy, Jane, Stephen and Luke. He jokes about his tight schedule, even seems proud of living on one meal a day and five hours of sleep per night and getting up to read or write at 4:30 every morning (except Sundays, when he sleeps in till seven). Two rare indulgences in this life-long marathon seem to be his hobby of heraldry and his 30-year-old sports car, a snazzy topless Allard, which he drives to work year round regardless of the weather.
As for Michelle, she's content to have a normal knee. After swimming, cycling, roller-skating, and playing tennis all summer, she's looking forward to winter so she can try out her new ski!