Knee arthroscopy has been a very popular operation for treating painful knees for more than 30 years. Unfortunately it doesn’t always work. Over the last few years a lot of research has been looking at which patients it works well in and which it doesn’t. From this we have figured out that there are two groups of patients with painful knees who get little or no benefit from knee arthroscopy. The first group is patients with osteoarthritis and the second group are atraumatic meniscal tears. I’ll go over both groups.