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Retrospective study.To evaluate the outcome of artificial cervical disk replacement (ACDR) for the treatment of adjacent segment disease (ASD) after anterior cervical decompression and fusion (ACDF).ACDF is the useful procedure for degenerative cervical diseases. However, studies have reported accelerated degeneration of functional spinal units adjacent to the fusion site after ACDF.Between January 2004 and January 2011, 32 inpatients (18 male, 14 female; age, 38–61 y; mean, 48 y) underwent ACDR for the treatment of ASD after previous ACDF (single-level: n=12; 2-level: n=15; 3-level: n=5). In 22 patients, ASD occurred above the fusion site, and in 10 it occurred below the site. After ACDR, the patients were followed up for 30–62 months (mean, 49 mo). Before and after ACDR, patients were evaluated using the pain visual analog scale (VAS), the Japanese Orthopedic Association (JOA) score, and neck disability index (NDI). In addition, the range of motion (ROM) of the replaced and adjacent unfused segments was measured by flexion/extension lateral radiography. Periprosthetic heterotopic ossification was detected using McAfee’s classification. Degeneration of the adjacent unfused segment was evaluated using Goffin scale.All patients had successful surgery. Before ACDR, neck VAS, upper-limb VAS, JOA score, and NDI were 7.2±1.8, 6.9±1.1, 9.8±2.5, and 40.5±4.8, respectively. At the last follow-up, they were 1.2±0.3, 0.9±0.3, 14.5±1.1, and 9.0±2.5, respectively. Compared with presurgery, the improvements in VAS, JOA score, and NDI at the final follow-up were statistically significant (all P<0.05). During follow-up, prosthesis positioning was satisfactory without migration or downward movement. Preoperatively, the ROMs of the replaced and adjacent segments were 8.7±2.6 and 7.6±3.0, respectively. At the last follow-up, they were 8.5±2.2 and 7.2±2.6, respectively (both P>0.05). At the last follow-up, 2 patients had grade II heterotopic ossification; 3 patients had aggravated degeneration (vs. preoperative status) of the adjacent unfused segment. However, the reduction in Goffin grade was not statistically significant.Our follow-up shows that ACDR is an effective treatment for post-ACDF ASD. It can maintain the ROMs of the replaced segment as well as the adjacent unfused segment.