Weakness of the left knee going up stairs needs to be treated according to the cause of the disease, generally there are rest, physical therapy, drug therapy and surgical treatment and other methods. 1. Excessive fatigue: due to excessive fatigue caused by lower limb muscle strain, local lactic acid metabolites can not be absorbed in time, the patient may appear left knee weakness. Treatment mainly takes rest, most of the patients can be significantly relieved after sufficient rest. 2. Trauma: due to trauma caused by knee fractures, muscle and other soft tissue injuries, patients can appear left knee weakness, pain, swelling and other symptoms. Conservative treatment can be used when the injury is mild, such as local plaster or brace fixation, rest, early cold compresses and other physical therapy, the use of non-steroidal painkillers such as celecoxib. Surgery can be used when the injury is serious. 3. Lumbar spine disease: commonly caused by lumbar spine degeneration sciatic nerve compression, causing lower limb weakness, numbness and other symptoms, patients may appear left knee weakness to go up the stairs. Treatment is based on conservative treatment, such as bed rest, localized hot compresses, baked electricity and other physiotherapy, Loxoprofen anti-inflammatory drugs, if necessary, surgical treatment. 4. Knee joint lesions: such as knee rheumatism, rheumatoid arthritis, osteoarthritis and other diseases, patients can appear left knee weakness upstairs. Treatment is mainly conservative treatment, such as local hot compress physiotherapy, celecoxib and other anti-inflammatory drugs, if necessary, surgical treatment. Weakness of the left knee is recommended to consult a doctor in time, with the help of the doctor to clarify the cause of the disease, and to carry out targeted treatment or treatment.