A 15-year-old male reports dull pain in both knees. Sometimes one or both knees click, and the patient describes a catching sensation under the patella. In determining the causes of the knee pain, what additional history do you need? What categories can you use to differentiate knee pain? What are your specific differential diagnoses for knee pain? What physical examination will you perform? What anatomic structures are you assessing as part of the physical examination? What special maneuvers will you perform?