(arteriosclerosis obliterana, ASO) is a chronic disease with clinical manifestations of limb ischemia caused by atherosclerotic changes in the arteries of the lower extremities due to arterial stenosis or occlusion, often as a manifestation of systemic atherosclerotic disease in the lower extremity. Etiology: hypertension, diabetes, hyperlipidemia, hyperuricemia, history of smoking, advanced age and other high-risk factors. Clinical symptoms: Early symptoms such as cold limbs and intermittent claudication are often easily overlooked. The symptoms of intermittent claudication then worsen (the distance is shortened from one or two stops to 50 meters away). Intermittent claudication is one of the main clinical manifestations of ASO of the lower extremities. It refers to fatigue, discomfort or pain confined to specific muscle groups of the lower extremities caused by ischemia and hypoxia in the extremities after walking, which can be relieved after stopping activities. The symptoms can be repeated after walking again. Ischemic rest pain (rest pain) is one of the main clinical manifestations of severe ischemia of the limb caused by ASO of the lower limb. When the ischemia is severe, the limb has persistent pain at rest at night. Further development of severe lower limb ischemia (Critical Limb Ischemia, or CLI) refers to the severe stage of lower limb ASO, with typical clinical manifestations including rest pain, ulceration, and gangrene. This stage is characterized by poor treatment outcome, high amputation rate and mortality (cardiovascular and cerebrovascular accidents). Patients with lower extremity atherosclerotic occlusive disease are advised to understand their condition and seek timely medical attention. Understanding the clinical classification and grading of lower extremity atherosclerotic occlusive disease helps to determine the clinical progression and severity as a reference for drug, interventional or surgical treatment. The Fontaine and Rutherford classifications are commonly used clinically. Fontaine classification of lower extremity ASO: Stage I: asymptomatic Stage IIa: mild intermittent claudication Stage IIb: moderate or severe intermittent claudication Stage III: resting pain Stage IV: tissue ulceration, gangrene Rutherford classification of lower extremity ASO: Grade 0: asymptomatic Grade 1: mild intermittent claudication Grade 2: moderate intermittent claudication Grade 3: severe intermittent claudication Grade 4: resting pain Grade 5: mild Tissue defects Grade 6: Tissue ulceration, gangrene