Historically, scientists have believed that the placebo effect didn’t have any role in surgery. It has been long thought that the placebo was a suggestion more related to mental effect than otherwise. But things changed with a study  carried out in Australia that was surprising. It was about to validate the arthroscopic surgery in patients with oesteartritis.
They made three groups, one simply subjected to arthroscopic lavage in which the joint was washed with at least 10 liters of fluid to remove any particles. In this case no mechanical instrument was used to remove tissue (only in case of a tear in the meniscus this tear was removed and smoothed); another group with lavage and debridement, in which they eliminated any part of degenerate meniscus; and the third group was the control group with sham surgery. The patients in this group underwent arthroscopic incisions and were subjected to sham surgery during which the surgeon simulated operation. The surgeons thought the sham surgery would have no effect. All operations were performed by the same surgeon.
It was surprising that the results showed no significant difference in pain reduction between the control group and placebo or sham surgery . No significant differences between the actual surgery group and the sham surgery were found in terms of the ability to walk and bend the knee after one and two years . The degree of confidence to exclude any clinically significant difference in these parameters between the placebo group and the other was 95 %.
 A Controlled Trial of Arthroscopic Surgery for Osteoarthritis of the Knee. 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.