Soreness on the inner side of the left leg joint when squatting may be caused by meniscus injury, knee synovitis, osteoarthritis and other diseases, which need to be treated with medication, surgery or other treatments. 1. Meniscus injury: the common symptoms are pain and swelling of the affected knee, and the pain will be aggravated when moving. Patients need to follow the medical advice to apply ibuprofen, aspirin and other non-steroidal anti-inflammatory drugs. If conservative treatment is not effective, patients need to consider meniscus repair, meniscectomy and other surgical treatments. 2. Knee synovitis: patients mainly manifested as knee joint swelling, pain, activity limitation. Patients need to follow the medical advice to apply indomethacin, acetaminophen and other non-steroidal anti-inflammatory drugs, if accompanied by bacterial infection, need to follow the medical advice to apply amoxicillin, azithromycin and other antibiotics. If accompanied by rheumatoid arthritis need to apply glucocorticoids, such as prednisone, dexamethasone and so on. If non-surgical treatment is ineffective for more than 2 months, surgical treatment such as lesion debridement or arthroscopic biopsy should be considered. Secondly, infrared ray, ultrasonic wave, ultrasonic wave, ion introduction method and other physical therapy can also be taken. 3. Osteoarthritis: Typical symptoms include joint soreness, distension, pain or pressure, joint stiffness and so on. Patients should follow the doctor’s instructions to apply non-steroidal anti-inflammatory drugs such as diclofenac and naproxen, as well as cartilage protectors such as glucosamine hydrochloride and bisacodyl, and glucocorticosteroids such as methylprednisolone and hydrocortisone. If medication is not effective, surgical treatment such as arthroscopic cleaning and joint fusion should be considered. Secondly, physical measures such as massage, acupuncture, hydrotherapy and heat therapy can also be used. There are many other causes of left leg pain when squatting, patients need to go to the hospital in time and cooperate with the doctor to actively treat the primary disease.