Soreness and swelling of the inner side of the knee may be caused by knee injury, osteoarthritis of the knee, acute synovitis of the knee and so on. 1. Knee joint injury: In the process of running and jumping and other sports, the knee joint is easy to be strained, or beyond the capacity of the knee joint, resulting in injury to the knee joint, and in the early stage will show the symptoms of soreness and swelling of the inner side of the knee. 2. Osteoarthritis of the knee: it may be related to heredity, patient’s age, obesity, inflammation, trauma and other factors, etc. Osteoarthritis is triggered by a variety of factors, and its symptoms such as soreness and swelling of the inner side of the knee will appear in the early stage after being cold, exertion or minor trauma. 3. Acute knee synovitis: It may be caused by trauma that ruptures and congests the synovial membrane, produces a large amount of fluid and bleeding, and leads to obstruction of the lymphatic circulation that triggers acute knee synovitis. There is often a history of trauma to the knee or short-term overuse of the knee, and symptoms such as soreness and pain on the inner side of the knee may occur during an attack. There may be other reasons for the soreness on the inner side of the knee. It is recommended to go to a regular hospital in time, complete the relevant examinations, clarify the cause of the disease, and then carry out targeted treatment or therapy under the guidance of the doctor.