Pain in the medial side of the foot can be caused by localized injury, degenerative disease of the foot structure and abnormal development of the medial side of the foot. 1. Local injuries: If the patient has strenuous exercise or stands and walks for a long period of time, it may lead to damage of the local muscles or tissues, which may lead to the phenomenon of medial plantar facet pain. 2. Degenerative lesions of the foot structure: If the patient has degenerative lesions of the foot structure, aseptic inflammation may occur after mild activities, leading to pain in the inner side of the foot. For example, plantar fasciitis is more common in clinical practice. 3. Abnormal development of the medial side of the foot: If the patient has abnormal development of the foot such as flatfoot syndrome and valgus deformity, it may also lead to pain in the medial side of the foot after a certain amount of activity. Therefore, it is recommended that patients go to the hospital in time to consult the doctor, after clarifying the cause of the disease, follow the guidance of professional doctors and actively carry out treatment.