CliniCal artiCle J neurosurg Spine 25:556–565, 2016 abbreviationS ACDF = anterior cervical discectomy and fusion; AE = adverse event; AP = anteroposterior; ASD = adjacent-segment disease; BMI = body mass index; COI = conflict of interest; COR = center of rotation; cTDR = cervical total disc replacement; FJD = facet joint degeneration; HO = heterotopic ossification; NDI = Neck Dis- ability Index; RCT = randomized controlled trial; ROM = range of motion; VAS = visual analog scale. SUbMitteD July 9, 2015. aCCePteD March 3, 2016. inClUDe when Citing Published online June 3, 2016; DOI: 10.3171/2016.3.SPINE15810. Four-year results of a prospective single-arm study on 200 semi-constrained total cervical disc prostheses: clinical and radiographic outcome hans-Jörg Meisel, MD, PhD, 1 lubomír Jurák, MD, 2 Jussi antinheimo, MD, 3 ricardo arregui, MD, 4 bernhard bruchmann, MD, 5 Mario Čabraja, MD, 6 Fabrizio Caroli, MD, 7 Stefan Kroppenstedt, MD, 8 Jan Kryl, MD, 9 Juha Pohjola, MD, 3 ian Shackleford, MD, 10 Steffen Sola, MD, 11 Peter Stosberg, MD, 1 Jan Stulik, MD, 9 Christian woiciechowsky, MD, 12 and Petr Suchomel, MD 2 1 Department of Neurosurgery, BG Clinic Bergmannstrost, Halle, Germany; 2 Neurocentre, Regional Hospital Liberec, Czech Republic; 3 Department of Neurosurgery, University of Helsinki, Finland; 4 Neurosurgical Department, Hospital Maz, Zaragoza, Spain; 5 Spinal Surgery, Katholisches Klinikum Koblenz, Germany; 6 Zentrum für Wirbelsäulenchirurgie, Vivantes Auguste- Viktoria-Klinikum, Berlin, Germany; 7 Neurosurgery, “Regina Elena” National Cancer Institute, Rome, Italy; 8 Abteilung für Wirbelsäulenchirurgie, Sana Kliniken Sommerfeld, Kremmen, Germany; 9 Center for Spine Surgery, Motol University Hospital, Prague, Czech Republic; 10 Spinal Surgery, Warrington District General Hospital, Warrington, United Kingdom; and 11 Department of Neurosurgery, University of Rostock, Germany; and 12 Neurosurgery and Spine Surgery, Spine Center Berlin, Germany obJeCtive Recent studies have described encouraging outcomes after cervical total disc replacement (cTDR), but there are also critical debates regarding the long-term effects of heterotopic ossifcation (HO) and the prevalence of adjacent-level degeneration. The aim in this paper was to provide 4-year clinical and radiographic outcome results on the activ C disc prosthesis. MethoDS A total of 200 subjects underwent single-level activ C (Aesculap AG) implantation between C-3 and C-7 for the treatment of symptomatic degenerative disc disease. Clinical and radiographic assessments were performed preoperatively, intraoperatively, at discharge, and again at 6 weeks, 6 months, 1 year, 2 years, and 4 years. Radiographic evaluations were done by an independent core laboratory using a specifc software for quantitative motion analysis. reSUltS Neck Disability Index (NDI) and visual analog scale (VAS) score for neck and arm pain decreased signif- cantly from baseline to the 4-year follow-up. The mean improvement for NDI was 20, for VAS severity and frequency of neck pain 26.4 and 28, and for VAS severity and frequency of arm pain 30.7 and 35.1, respectively. The neurological situation improved for the majority of patients (86.4%); 76.1% of cases were asymptomatic. Subsequent surgical interven- tions were reported in 7% of the cases, including device removals in 3%. In 2.5% a subsidence greater than 3 mm was recorded; 1 of these cases also had a migration greater than 3 mm. No device displacement, expulsion, disassembly, loose or fractured device, osteolysis, or facet joint degeneration at the index level was observed. Segmental lordotic alignment changed from - 2.4° preoperatively to -6.2° at 4 years, and postoperative height was maintained during the follow-up. Advanced HO (Grade III and IV) was present in 27.1% of the cases; 82.4% showed segmental mobility. A pro- gression of radiographic adjacent-segment degeneration occurred in 28.2%, but only 4.5% required surgical treatment. ConClUSionS The activ C is a safe and effective device for cervical disc replacement confrming the encouraging results after cTDR. Clinical trial registration no.: NCT02492724 (clinicaltrials.gov) http://thejns.org/doi/abs/10.3171/2016.3.SPINE15810 Key worDS cervical spine; total disc replacement; degenerative disc disease; activ C; clinical outcome; long-term results; Neck Disability Index; visual analog scale; heterotopic ossification; range of motion; adjacent-segment degeneration ©AANS, 2016 J neurosurg Spine Volume 25 • November 2016 556