How often is adjacent segment disease reported? A systematic review of prospective studies comparing total disc arthoplasty versus ACDF

After a systematic review, six prospective studies comparing TDR versus ACDF were selected. These studies had between 2-5 years follow-up and reported revisions due to adjacent segment disease. The concern for adjacent segment disease (ASD) has led to the development of motion-preserving technologies such as total disc arthoplasty (TDA). However, numerous studies comparing ACDF versus TDA do not report the number of patients who develop symptoms attributable to an adjacent level or the number of revisions that occur at an adjacent level. Often the follow-up period is limited as well. A systematic review of IDE and non-IDE trials was performed using PubMed and Cochrane Libraries. These databases were thoroughly searched for prospective randomized studies comparing ACDF and TDR. Specifically, studies reporting clinical outcomes and symptomatic ASD with at least 2 years of follow-up were selected. Six studies met the inclusion criteria and are discussed in the review. Pooling data from six prospective studies, the overall sample size at baseline was 1586 (ACDF = 777, TDA = 809) and at final follow-up was 1110, giving an overall follow-up of 70%. Of 1586 surgically treated patients, 51 (3.2%, ACDF = 30, TDA = 21) required revision surgery at an adjacent level at 2-5 years of follow-up. There was no data available on the incidence of ASD or the number of patients with ASD treated non-operatively. There has not been a study to date that has demonstrated a difference in the rate of ASD for ACDF versus TDR. There is a paucity of data from prospective studies regarding the incidence of ASD and the proportion of patients who go on to require further surgical intervention. Prospective studies should continue to focus on excellent patient follow-up and accurate assessment of patient symptoms as ASD has been under reported in prospective studies.