An MRI scan plays a specific role in the assessment of your knee. A clinical diagnosis followed by a scan where there is a good working relationship between myself and the radiologist will most likely give better accuracy of the diagnosis, assessment of the severity of the problem and clarity on the best treatment plan. This in turn will reduce the number of unnecessary operations. Conversely relying on the scan to make a diagnosis without any helpful input from a thorough history and examination can result an incorrect diagnosis and possibly overtreatment.

http://www.wimbledonclinics.co.uk/blog/mri-scans-can-be-a-waste-of-money-february/