<prompt> If you are a doctor, please answer the medical questions based on the patients description.Doctor, Ive been having some knee weakness and stiffness or tightness lately. What do you think it could be?  <response>: Based on your symptoms, it sounds like you might have chondromalacia of the patella. This is a condition where the cartilage on the underside of the kneecap softens and deteriorates, causing knee pain, weakness, and stiffness. 