1. Fat pad strain The fat pad fills the gap at the front of the knee joint and has the function 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 movement. 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. 2, meniscal injury Meniscal injury is a common injury in athletes. When the lower limb is weighted, the foot is fixed, and the knee is slightly flexed, a sudden excessive internal rotation of the knee extension or external rotation of the knee extension (for example, in volleyball, the player suddenly turns and fishes to save the ball while defending) may cause a meniscal tear. A meniscal injury can be characterized by a distinct tearing sensation in the knee, followed by joint pain, limited motion, and a walking limp. The joint exhibits swelling and slipping sensations and pops when the joint is moved. 3.Knee traumatic synovitis Knee traumatic synovitis knee synovium is one of the main structures that make up the knee joint. Synovial cells secrete synovial fluid, which can keep the cartilage surface of the joint slippery and increase the range of motion of the joint. Injury to the synovial membrane due to trauma or overexertion can produce a large amount of fluid, which increases the pressure in the joint and, if not eliminated in time, can easily cause joint adhesions and affect normal activities. Patients will feel pain, swelling and pressure in the knee joint, and the synovial membrane has a frictional sound. The most obvious feature of the pain is that when the knee joint is actively and extremely extended, especially when there is a certain resistance to do the knee extension movement, the pain in the lower part of the patella will be increased, and the pain is also significantly increased when it is passively and extremely flexed. 4, osteoarthritis of the knee joint Osteoarthritis of the knee joint is a condition seen in middle-aged and elderly people, mostly women. Overload is the main cause of the disease. The knee joint will be swollen and painful, and sometimes there will be friction sounds when moving the joint. The knee may have an inversion deformity and be accompanied by medial pain. 5. Knee ligament injury Knee ligament injury is relatively less stable when the knee is slightly flexed. If a sudden external force causes valgus or inversion at this time, it may cause medial or lateral collateral ligament injury. Medial collateral ligament injuries account for the majority of clinical cases. In this injury, for example, the patient will have a clear history of trauma, pain and pressure on the medial side of the knee, increased pain with passive abduction of the lower leg, and swelling on the medial side of the knee, with petechiae appearing after a few days. Knee movement will be limited. 6, inadequate warm-up before exercise Many people exercise, often first do leg stretching exercises, not knowing that leg stretching exercises are the main cause of knee injury prone. When exercising, the knee has to withstand enormous pressure, so it must be properly warmed up to avoid injury. Exercise without warming up is the same as not giving the joints natural lubrication, and the knee joint certainly does not run smoothly. In addition, cold, tense muscles are also detrimental to the smooth functioning of the joint. Suddenly start or end the movement, will tear the muscles around the joint, causing or exacerbating overuse injuries. 7, over-exercise Over-exercise is often counterproductive and not only reduces physical fitness, but is also a factor in knee injuries. If you feel discomfort in your knee while exercising, that is acceptable; if you feel pain after doing exercise, or the next day, the situation is not good. Prolonged pain, limping and swelling around the knee are all warning signs of a knee injury and should be seen by a doctor immediately.