Lumbar adjacent segment degeneration is defined as degenerative changes cranial or caudal to surgical segments.Some patients developed corresponding clinical symptoms in addition to radiological degeneration,which is called adjacent segment disease.Although many new surgical techniques emerged in recent years,the problem of adjacent segment degeneration has not really been resolved.MEDLINE/PubMed,Cochrane Controlled Trials Registry and EMBASE were comprehensively searched.All randomized or nonrandomized clinical studies of lumbar degenerative diseases treated by fusion/fixation,decompression-alone or artificial lumbar disc replacement were included.The number of cases enrolled in these studies was greater than or equal to 20 cases and the minimum age of the patients was 18 years old.Case reports,reviews or meta-analyses,papers with unobtainable text and abstract,and studies of trauma,infection,oncology and inflammatory disease were all excluded.The diagnostic criteria of adjacent segment degeneration,as well as the incidence and risk factors of adjacent segment degeneration and reoperation were reviewed.The concepts of adjacent segment degeneration in different literatures were very confusing,and radiological degeneration was often mixed in use with symptomatic degeneration.It was therefore difficult to make any conclusion due to lack of a standard.In addition,the previous studies did not fully understand the pathogenesis and risk factors of the disease,especially the effect of the index level on adjacent segments.Moreover,most of the current studies were retrospective,therefore,convincing conclusions can hardly be drawn due to lack of high-level evidence.The main reason for reoperation after lumbar fusion is adjacent segment degeneration.Therefore,the most important way to reduce the rate of reoperation is to reduce the incidence of adjacent segment degeneration.In the future,the diagnostic criteria for adjacent segment degeneration should be unified first.And it is extremely important to thoroughly understand the mechanism and risk factors of adjacent segment degeneration by comprehensive studies and clarify them through high-level evidence.