The Power of the Placebo: Clinical Trial of Arthroscopy for Knee Osteoarthritis

A recent clinical trial published in the New England Journal of Medicine has posed more questions than it answers. The conclusion of the study was that arthroscopic surgery for osteoarthritis (OA) of the knee doesn’t work, but the study has turned up some fascinating information about the placebo effect.

The surgery that has been proposed by orthopaedic surgeons in the past is a result of the fact that no one really knows what causes the pain in OA. Some propose that lavage removes debris such as microscopic or macroscopic fragments of cartilage that may induce synovitis, a likely source of pain. Others propose that the roughened surfaces might be producing some of the pain and that debridement consisting of smoothing rough, fibrillated articular and meniscal surfaces, shaving tibial-spine osteophytes that interfere with the motion of the joint, and removing inflamed synovium would reduce the pain. Thus there were 2 schools of thought amongst surgeons: those who believed that if you washed out all the unwanted fluid and enzymes, they might feel better, or alternatively if you sanded off the rough surfaces then it might relieve the pain.

A total of 180 patients with OA of the knee were randomly assigned to receive arthroscopic debridement, arthroscopic lavage, or placebo surgery. One orthopaedist performed all the operations.

The patient’s who were to have placebo surgery received an intravenous valium-like drug and intravenous narcotics. Three 1cm skin incisions were made over the knee exactly like a patient who undergoes the normal procedure. Then, in case the patient may have woken up slightly during the procedure, the surgeon asked for all instruments to be present, and put the knee through all movement as if the procedure was done. In addition, in a regular procedure the large volume of fluid that is washed to the joint is caught in a basin and makes splashing noises. So they had someone sitting by the table splashing water so they would hear that. Patients were very unlikely to guess placebo in any of the groups.

The subjects were followed for up to 2 years and the result was that there was no benefit from the operations. In fact those who’d had the arthroscopic debridement tended to be worse off.

The investigators did find that the people who came out best of all were those who’d had the strongest belief that the procedure was going to help them. It is suggested that this was probably the result of an almost universal trait among orthopaedic surgeons – to have absolute, unshakeable confidence in their skills.

The investigators are now studying the placebo effect further. They are trying to determine what environment and what setting in the health care environment, and in the doctor-patient communication, or in the interchange between doctors and patients, that leads some patients to have beneficial outcomes. The investigators are looking at harnessing the placebo effect to develop an inexpensive, but very effective, low risk treatment that has about a 35% beneficial effect.

Placebos can be powerful agents for something that is supposed to be “biologically inert”. They can stop an asthmatic wheezing, cause pain or relieve it, and even make Parkinson’s patients walk again. Placebos can be pills, potions, procedures or people. Placebos are known to be more effective if the effect is subjective, such as a reduction in pain or depression. Injections have more placebo effect than tablets, while the best placebo is surgery.

Chiropractors and osteopaths have no doubt utilised the placebo effect for many years. Considering that our patients generally consult us because they are in pain, the evidence suggests that we are in good stead to decrease this pain no matter what we do – just tell them that they will feel better and they will! How much of our therapy is due to a real biological effect, and how much is due to placebo will be the subject of much scrutiny in this current environment of evidence-based health care.

Simon French

Source: Moseley JB, O’Malley K, Petersen NJ et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. NEJM 2002;347(2):81-8