the power of placebo is strong in this one

A little while ago, when I wrote a post on homeopathy, I mentioned the placebo effect. All the science-based commentaries I’ve read on homeopathy indicate that it achieves its apparent results via placebo: the patient expects to get better, & in some cases they do (eg report fewer symptoms, less pain, & so on). Now, the placebo effect could well be effective in cases where a friendly discussion of their problems & a homeopathic remedy contribute to a feeling of well-being, but what about something like surgery? Surely the placebo effect wouldn’t be operating there as well?

The answer is – yes, yes it could.

A few years ago now I heard about a case where surgeons compared the effects of actual keyhole surgery for pain due to arthritis in the knee joint, and placebo treatment. I’ve mentioned it in lectures before now, but I thought it might be useful to find the original paper (Mosely et al. 2002) & find out the details of what went on.

Osteoarthritis in the knee joint can be extremely painful & can significantly reduce a sufferer’s mobility. In the US, according to Moseley & his co-workers (2002), doctors in the US performed more than 650,000 keyhole surgery operations each year to wash out the joint (lavage) & in many cases surgically remove torn or damaged cartilage (debridement). However, while up to 50% of patients apparently report that this surgery relieved their pain, the authors comment that the physiological basis for the pain relief is unclear [and] there is no evidence that arthroscopy cures or arrests the osteoarthritis. So, to test the effectiveness of this surgery, the research team designed a randomised, placebo-controlled trial. All their participants (N = 180) reported moderate to severe knee pain that wasn’t relieved by normal medical treatments, & had not recently had an operaton to relieve that pain. The patients were randomly assigned to one of 3 treatments, so this was what’s called a blinded study. (Obviously the surgeons couldn’t be blinded, but they didn’t find out the treatment until the paitient was actually in the operating room.) This is the experimental method:

Participants were randomly assigned to arthroscopic debridement, arthroscopic lavage alone, or the placebo procedure. One [surgeon] performed all the operations. Patients in the debridement group or the lavage group received standard general anaesthesia with endotracheal intubation (that thing where a ttracheal tube delivers a mix of oxygen & anaesthetic gases to the lungs)Patients in the placebo group received a short-acting intravenous tranquiliser and an opioid and simultaneously breathed oxygen-enriched air. In addition, while the first 2 groups had the actual operation, the placebo patients had the same keyhole incisions made in their knee, & the surgeon spoke & acted as if the actual operation was being performed – this was in case the patients turned out to have some recall of what went on despite the anaesthesia, so they wouldn’t realise that they were in the placebo group. And they received exactly the same pre- & post-operative care as the ‘real’ patients.

The outcome? There was no difference in reported knee pain between the placebo group & those who’d had the actual treatments, when they were surveyed one year after the operation & again a year after that. And tellingly, at no time point did either arthroscopic-intervention group have significantly greater improvement in function than the placebo group. The team concluded that arthroscopic lavage with or without debridement is not better than and appears to be equivalent to a placebo procedure in improving knee pain and self-reported function (Moseley et al. 2002).

In other words, the placebo effect can be extremely powerful – if patients expect to feel better, they may, even if nothing substantive has actually been done or given to them. This is an important thing to remember when assessing claims for the efficacy of a particular treatment, whether it be mainstream medicine or something more ‘alternative’.

And for another example of this, read Orac’s comments on vertebroplasty.

J.B.Moseley, K.O’Malley, N.J.Petersen, T.J.Menke, B.A.Brody, D.H.Kuykendall, J.C.Hollingsworth, C.M.Ashton & N.P.Wray (2002) A controlled trial of arthroscopic surgery for osteoarthritis of the knee. New England Journal of Medicine 347(2): 81-88  

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