Inclusion Criteria:  For patients undergoing revision surgery in adjacent segments due to S-ASD, the revision surgery is at least half a year from the first operation; X-ray, CT and MRI examination data of the anterior and lateral extension of the lumbar spine were available within 1 month before surgery and at the last follow-up; Follow-up for at least 2 years after revision;  Exclusion Criteria:  Patients with history of congenital spinal deformity, spinal tumor, spinal tuberculosis.