New Study Sheds Light on Effectiveness of Total Knee Replacement Surgery

Having reached the age at which some of my joints are likely to need replacement by artificial ones, all the more likely because of an old knee injury, I was interested to read a controlled trial recently published in the New England Journal of Medicine of total knee replacement compared with non-surgical treatment of osteoarthritis of the knee. About 670,000 knee replacements are undertaken annually in the United States, and no doubt a similar number in Europe, so it would be a good idea to know if they worked, or rather worked more than the alternative. You don’t need to know many people who have had a knee replaced to know that they work, but that is not the question.

The authors of the paper in which their trial is reported claim that, before theirs, there had never been a controlled trial of total knee replacement to establish whether the surgery is really beneficial by comparison with other types of treatment. The recommendation of surgeons to patients was previously based on their mere observation, almost certainly correct, that patients benefited from surgery.

The trial, conducted in Denmark, took a hundred patients who would normally have been eligible for total knee replacement according to the surgical criteria laid down for it and divided them at random into two groups of fifty, the first given surgery and the second a twelve-week program of treatment (that the surgical patients also had after their operation). This consisted of pharmacological pain relief, dietary advice to reduce weight (excess weight being understandably harmful for knees), exercise, the use of insoles, and education by physiotherapists. The results were assessed and compared after twelve months.

The average age of the patients was about 65 and their average Body Mass Index was 32. This meant that they were considered, on average, to be moderately obese, which suggests that obesity is a cause of, or at least an exacerbating factor for, osteoarthritis sufficiently severe to justify replacement surgery. Not only is the population aging, but it is getting fatter, so that more and more such surgery will become necessary.

The results at twelve months were, for once, very clear cut (they were assessed by people who did not know to which group, surgical or non-surgical, the patients belonged, to avoid bias in their assessments). On all measures used, the surgical patients did better than those who did not have surgery. They suffered considerably less pain, their general level of satisfaction with life was higher, and they were able to move better, for example as measured by something called the up-and-go test, which measures the time (in seconds) taken to rise from a chair, walk ten feet, return, and sit down again.

The authors acknowledge that the trial was not perfect because the patients who had the surgery knew that they had had it, of course, and those who did not have it knew that they had not. Ideally, it should have been a trial of real against sham surgery, because surgery itself can have a powerful placebo effect irrespective of any other benefit. Moreover, patients who did not have it may have been disappointed and thus had a nocebo effect (the placebo effect in reverse). This means that the beneficial effect of surgery might have been exaggerated in this trial, although the difference in results was too great to be plausibly accounted for in this fashion.

However, 24 of the patients with knee replacements experienced “serious adverse events” in the 12 months after treatment, compared with only 6 of the patients given non-surgical treatment, and most importantly only 13 of the latter patients went on to have total knee replacements within the 12 months. Perhaps, then, everyone eligible for total knee replacement ought to have a trial of non-surgical treatment first: with the important caveat that, since this trial did not include those who suffered the most severe pain from osteoarthritis, those in the severest pain ought to proceed directly to surgery.