Some doctors have asked this very question. Yet it's hard to beat the safeness and accuracy of knee arthroscopy. Other diagnostic procedures, such as MRI, tend to be more costly and less accurate. And in some clinics, patients have to wait longer to get them. For these reasons, knee arthroscopy remains the most popular way to look for the source of knee pain.
Even "normal" knee arthroscopy results--or finding no abnormality--may benefit the patient. A recent study found that patients with these results were doing much better a few years later. It's possible that, after learning there were no abnormalities, patients learned to live with their symptoms. Or there could be some benefit from the procedure itself. In any case, a high percentage of "normal" knee arthroscopies may not be such a bad thing, after all.