Walking pain in the lower corner of the medial side of the left knee may be due to meniscus injury or other causes, such as popliteal cyst and synovitis. 1. Meniscus injury: there are two kinds of meniscus injury, one is violent trauma when the knee joint is twisted, and the other is injury caused by long-term weight bearing, which will cause different degrees of pain, usually accompanied by swelling, joint popping, joint interlocking and other symptoms. 2.Other injuries (1) Popliteal cyst: popliteal cyst is often accompanied by inflammatory disease of the knee, when the pressure in the joint cavity is abnormally high the joint fluid will flow out through the gap, so that the bursa will be enlarged, which will form a popliteal cyst, and the symptom of pain in walking on the medial lower corner of the left knee can occur. (2) synovitis: synovitis is a variety of causes of synovial inflammatory changes, due to inflammation stimulation of the patient, there will be redness, swelling, burning, pain and other symptoms around the joints, and there will also be a significant limitation of joint activity, there will also be a walking pain in the lower corner of the inner side of the left knee. Left knee medial lower foot walking pain may also have other factors caused by the patient is recommended to go to the hospital in time for a detailed examination, to clarify the cause for targeted treatment.