Frequent causes of knee pain: 1, knee synovitis Refers to acute trauma or chronic strain on the knee joint, causing synovial injury or rupture, the function of the synovial membrane abnormalities will cause the normal production and absorption of joint fluid in the knee joint, resulting in a non-infectious inflammatory reaction disorder in the knee joint cavity blood or fluid accumulation. It can be divided into acute traumatic synovitis and chronic injury synovitis. Acute traumatic synovitis occurs in young people who love sports; chronic injury synovitis occurs in middle-aged and elderly people who are obese or who overuse the knee joint for weight bearing. In young people, knee synovitis is mainly caused by causes of knee trauma, such as meniscal injury, synovial injury, cruciate or collateral ligament injury, intra-articular fluid accumulation or sometimes blood accumulation, manifested as acute traumatic knee synovitis. Intra-articular injuries and dislocations can sometimes be due to simple synovial injuries of the knee, such as mild trauma, or long-term chronic knee strain. Synovitis of the knee in the elderly, these elderly people are years of knee pain, severe cartilage wear, bone deformation (rotundity), peripheral osteophytes, after strain and attacked by wind, cold, dampness, knee synovial edema, exudate and effusion, etc. 2. Meniscal injury is a sudden rotational injury to the knee joint during exercise in young people, and in the chronic degenerative process in the elderly. The main manifestations are obvious pain, swelling and effusion in the knee joint during the acute phase, and impaired joint flexion and extension activities. After the acute phase, the swelling and effusion may subside on their own, but there is still pain in the joint when moving, especially when going up and down stairs, going up and down slopes, squatting and standing, running and jumping, etc. In severe cases, there may be limping or dysfunction in flexion and extension, and in some patients, there is a jamming phenomenon in the knee joint and a popping sound when the knee joint is flexed and extended, and in time, there will be thigh muscle atrophy. It requires careful examination by experienced orthopedic surgeons. X-rays cannot show meniscal damage, but other bone and joint disorders can be ruled out. If meniscal damage is suspected, MRI is recommended, but it is expensive, so it is recommended not to be greedy for cheap and do MRI with too low a field strength, and you can choose more than 1.5T. 3, knee ligament injury Mainly medial collateral ligament injury, lateral collateral ligament (lateral ligament complex) injury; anterior and posterior cruciate ligament injury. 70% of the reasons are sports injuries, soccer and the opposing player’s foot in the occurrence of valgus injury, basketball with the ball over the man when the knee joint of the supporting leg occurs rapid twisting external rotation injury, after shooting a single leg landing sprain, skiing sports, high-speed decline when the skis inserted into the snow, the athlete was tripped and occurred. In skiing, the skateboard is inserted into the snow when sliding at high speed, and the athlete trips and falls and suffers an over-extension injury; tug of war, vaulting, box jumping, etc. are also prone to anterior fork ligament injuries; pedestrians in high-energy traffic accidents, falls on electric bicycles or some weak people fall accidentally, which may also lead to ligament injuries. Generally, after the injury, the knee joint has severe pain, swelling, subcutaneous petechiae, joint effusion and activity limitation, which seriously affects the work and life of patients. 4. Fat pad strain The fat pad fills the gap at the front of the knee joint, which has the effect of strengthening the joint stability and reducing friction. The cause of fat pad strain may be due to trauma or long-term friction that causes fat pad congestion, hypertrophy and inflammation, and adhesions with the patellar ligament, thus limiting knee joint activities. This injury occurs in people over 30 years of age who walk, hike or squat frequently. Patients may feel pain in the knee joint, which is worse when fully extended, but there is no restriction of joint movement. The symptoms are obvious after exertion. 5. N-fossa cysts are common, with discomfort or mild pain in the N-fossa, fullness of the N-fossa or a cystic mass is found, with no pressure or mild tenderness, and mobility is mostly unaffected, some are found unintentionally while bathing. Ultrasound or MRI examination can be performed. 6, goose foot bursitis goose foot bursa is located in the suture muscle, thin femoral muscle and semitendinosus muscle joint tendon stop in the proximal end of the tibia to form a joint stop, because the three tendons have a dense fibrous membrane connected, shaped like a goose foot and named. The etiology is that overuse or direct contusion can cause inflammation of the bursa of the goose foot, which is easily confused with the pain of medial collateral ligament injury or medial compartment osteoarthritis. Pain in the medial knee joint can be aggravated by repeated flexion and extension of the knee, and pressure pain below the medial joint line. 7. Osteoarthritis Osteoarthritis of the knee joint. This condition is mostly seen in middle-aged and elderly people, mostly women, aged more than 50 years. The pain is heavy at the beginning of the activity, pain when going up and down stairs, pain when squatting and standing, and can be relieved by rest. If left untreated, it can lead to joint deformity, and the knee joint often suffers from knee synovitis, ligament damage, meniscal damage, knee free body, N-fossa cyst, patellar tenderness, goose foot bursitis, etc., and inversion deformity (commonly known as “rotund leg”).