The following causes of knee pain are common: First, severe synovitis and osteoarthritis of the knee joint can lead to a large amount of joint fluid, which can protrude into the posterior popliteal fossa, forming a local popliteal cyst that can compress the surrounding nerves and cause painful symptoms in the knee bend, accompanied by swelling and limited movement of the knee joint, and an MRI or ultrasound can reveal obvious local lesions. Second, damage to the meniscus of the knee will also cause pain in the bend of the knee, which will be significantly worse when the patient flexes the knee. MRI and physical examination at the same time can confirm the diagnosis of meniscal damage to the knee, and the diagnosis rate is higher if arthroscopy is used. Early diagnosis and treatment of pain in the knee bend can lead to relief of clinical symptoms and, if necessary, minimally invasive arthroscopic surgery. Patients should usually strengthen knee joint protection, enhance knee joint stability and prevent knee joint disease.