hi , then you need to check if any osteoarthritic changes are present after consulting your orthopaedician, he may tell you to undergo X RAY. Diffraction Enhanced X-Ray Imaging (DEI) is ANOTHER METHOD NOWADAYS USED FOR DIAGNOSING THE SAME WHEREIN WE CAN VISUALIZE BOTH SOFT TISSUES AND BONY STRUCTURES. There can other causes like ligament tears, or due to overuse of your knees due to some repetitive movements like squatting,et.} can too cause nagging pain . the best way to deal with this situation is to first apply ice cubes at the place to soothe any inflammation if present. If in recent past you have had any fall/ or trauma, You need to get some advice from your doctor and undergo the needful investigations so that the cause can be known.