New England J Medicine 2002 (Jul 11); 347 (2): 81–88 ~ FULL TEXT
J. Bruce Moseley, M.D., Kimberly O'Malley, Ph.D., Nancy J. Petersen, Ph.D.,
Terri J. Menke, Ph.D., Baruch A. Brody, Ph.D., David H. Kuykendall, Ph.D.,
John C. Hollingsworth, Dr.P.H., Carol M. Ashton, M.D., M.P.H., and
Nelda P. Wray, M.D., M.P.H.
Houston Veterans Affairs Medical Center,
Baylor College of Medicine,
Houston, TX 77030, USA
BACKGROUND: Many patients report symptomatic relief after undergoing arthroscopy of the knee for osteoarthritis, but it is unclear how the procedure achieves this result. We conducted a randomized, placebo-controlled trial to evaluate the efficacy of arthroscopy for osteoarthritis of the knee.
METHODS: A total of 180 patients with osteoarthritis of the knee were randomly assigned to receive arthroscopic débridement, arthroscopic lavage, or placebo surgery. Patients in the placebo group received skin incisions and underwent a simulated débridement without insertion of the arthroscope. Patients and assessors of outcome were blinded to the treatment-group assignment. Outcomes were assessed at multiple points over a 24-month period with the use of five self-reported scores — three on scales for pain and two on scales for function — and one objective test of walking and stair climbing. A total of 165 patients completed the trial.
RESULTS: At no point did either of the intervention groups report less pain or better function than the placebo group. For example, mean (±SD) scores on the Knee-Specific Pain Scale (range, 0 to 100, with higher scores indicating more severe pain) were similar in the placebo, lavage, and débridement groups: 48.9±21.9, 54.8±19.8, and 51.7±22.4, respectively, at one year (P=0.14 for the comparison between placebo and lavage; P=0.51 for the comparison between placebo and débridement) and 51.6±23.7, 53.7±23.7, and 51.4±23.2, respectively, at two years (P=0.64 and P=0.96, respectively). Furthermore, the 95 percent confidence intervals for the differences between the placebo group and the intervention groups exclude any clinically meaningful difference.
CONCLUSIONS: In this controlled trial involving patients with osteoarthritis of the knee, the outcomes after arthroscopic lavage or arthroscopic débridement were no better than those after a placebo procedure.
From the FULL TEXT Article:
When medical therapy fails to relieve the pain of osteoarthritis of the knee, arthroscopic lavage or débridement is often recommended. More than 650,000 such procedures are performed each year  at a cost of roughly $5,000 each. In uncontrolled studies of knee arthroscopy for osteoarthritis, about half the patients report relief from pain. [2–16] However, the physiological basis for the pain relief is unclear. There is no evidence that arthroscopy cures or arrests the osteoarthritis. Therefore, we conducted a randomized, placebo-controlled trial to assess the efficacy of arthroscopic surgery of the knee in relieving pain and improving function in patients with osteoarthritis. Both patients and assessors of outcome were blinded to the treatment assignments.
This study provides strong evidence that arthroscopic lavage with or without débridement is not better than and appears to be equivalent to a placebo procedure in improving knee pain and self-reported function. Indeed, at some points during follow-up, objective function was significantly worse in the débridement group than in the placebo group.
Arthroscopy is the most commonly performed type of orthopedic surgery, and the knee is by far the most common joint on which it is performed.  Numerous uncontrolled, retrospective case series have reported substantial pain relief after arthroscopic lavage or arthroscopic débridement for osteoarthritis of the knee. [2–16] In the only previous double-blind, randomized, controlled trial of knee arthroscopy of which we are aware,  patients with minimal osteoarthritis as assessed by radiography were assigned to undergo arthroscopic lavage with either 3000 ml of fluid (treatment) or 250 ml of fluid (control) and were followed for one year. Both the treatment and the control groups reported improvement in function at 12 months, and although the report interprets the study as having proved the efficacy of lavage, there was no statistically significant difference between the groups in terms of the primary outcome at any point during follow-up.
To explain the improvement that has been reported after these procedures, some have proposed that the fluid that is flushed through the knee during arthroscopy cleanses the knee of painful debris and inflammatory enzymes. [4, 6, 9, 15, 16, 34] Others have suggested that the improvement is due to the removal of flaps of articular cartilage, torn meniscal fragments, hypertrophied synovium, and loose debris. [2–14] However, our study found that outcomes after arthroscopic treatment are no better than those after a placebo procedure. This lack of difference suggests that the improvement is not due to any intrinsic efficacy of the procedures. Although patients in the placebo groups of randomized trials frequently have improvement, it may be attributable to either the natural history of the condition or some independent effect of the placebo.
Because we found no evidence that lavage or débridement is superior to a placebo procedure, the question arises whether these arthroscopic procedures could have small but clinically important benefits that we missed because of our limited sample size. To evaluate this possibility, we determined the size of the clinical benefit that the trial was able to rule out, using the minimal important difference for each of our scales. Because estimates of minimal important differences based on different samples and different methods do not yield the same values, we used the midpoint of the range of available minimal important differences in order to test our hypothesis about the equivalence of the three procedures. For the great majority of comparisons, the 95 percent confidence intervals did not contain the minimal important difference, indicating that there was not a clinically important improvement that the study had simply failed to detect.
One surgeon performed all the procedures in this study. Consequently, his technical proficiency is critical to the generalizability of our findings. Our study surgeon is board-certified, is fellowship-trained in arthroscopy and sports medicine, and has been in practice for 10 years in an academic medical center. He is currently the orthopedic surgeon for a National Basketball Association team and was the physician for the men's and women's U.S. Olympic basketball teams in 1996.
The principal limitation of this study is that our participants may not be representative of all candidates for arthroscopic treatment of osteoarthritis of the knee. Almost all participants were men, because the study was conducted at a Veterans Affairs medical center. We do not know whether our findings may be generalized to women, although uncontrolled studies do not indicate that there are differences between the sexes in responses to arthroscopic procedures. [8, 10, 13] A selection bias might have been introduced by the fact that 44 percent of the eligible patients declined to participate in the study. We believe this high rate of refusal to participate resulted from the fact that all patients knew they had a one-in-three chance of undergoing a placebo procedure. Patients who agreed to participate might have been so sure that an arthroscopic procedure would help that they were willing to take a one-in-three chance of undergoing the placebo procedure. Such patients might have had higher expectations of benefit or been more susceptible to a placebo effect than those who chose not to participate.
If the efficacy of arthroscopic lavage or débridement in patients with osteoarthritis of the knee is no greater than that of placebo surgery, the billions of dollars spent on such procedures annually might be put to better use. This study has also shown the great potential for a placebo effect with surgery, although it is unclear whether this effect is due solely to the natural history of the condition or whether there is some independent effect. Researchers should reconsider the best ways of testing the efficacy of surgical procedures performed purely for the improvement of symptoms. In the debate about placebo-controlled trials of surgery, the critical ethical considerations surround the choice of the placebo. Finally, health care researchers should not underestimate the placebo effect, regardless of its mechanism.