In general, the size of the surgery can be interpreted in the following ways: first, it is difficult to do and takes a long time to complete, more than 3 or 4 hours relative to an experienced attending surgeon, such as the removal of a chronic osteomyelitis lesion for a one-phase anastomotic vascularized fibular graft, a hip revision that requires reconstruction of the acetabulum and simultaneous femoral compression and implantation; and second, it is dangerous, with a relatively high rate of surgical complications, such as atlanto-atlantoaxial in the cervical spine Surgery. At present, the country is still mainly to do the initial knee replacement, for experienced knee surgeons, it usually takes only an hour or so, the chance of surgical complications is not high, so the initial total knee replacement surgery is not considered a major surgery.