Introduction: We examine the propensity of adjacent segment disease (ASD) to occur above the level of an index anterior cervical discectomy and fusion (ACDF).

Methods: We report 888 consecutive patients who underwent ACDF for cervical spondylosis over a twenty-year period at a single institution. Of these patients, 108 had re-do surgery due to symptomatic ASD. Pre-operative, intra-operative, peri-operative, and post-operative data were collected via clinical notes and patient interviews. Patients were followed for an average of 92.4 ± 72.6 months after the index ACDF.

Results: In agreement with previous literature, we found the highest rates of cervical spinal degenerative disease requiring surgery at C5/C6, followed by C6/C7. Interestingly, neither the location of index ACDF, nor the length of instrumented fusion affected the propensity to develop ASD in a statistically significant fashion (p>0.05). However, patients were statistically more likely to develop ASD above the index fusion construct (p<0.01). This was also true for patients undergoing a second revision surgery due to recurrent ASD. Importantly, these findings are consistent with existing in vitro biomechanical data in cadaveric spines.

Conclusions: Although ACDF is a generally well-tolerated surgical treatment for cervical spondylosis, adjacent segment disease remains a poorly understood but highly morbid complication. In this study, neither the inherent location of index ACDF, nor the length of instrumented arthrodesis affected the propensity to develop ASD. However, patients were statistically more likely to develop ASD at the level above—compared to below—the index fusion construct. This was true even for patients experiencing recurrence of ASD after a second cervical fusion surgery. Importantly, our data are consistent with existing in vitro biomechanical studies in cadaveric spines. Our findings support the theory that iatrogenically introduced stress and instability at adjacent spinal segments may contribute to the pathogenesis of adjacent segment disease.

Patient Care: This abstract focuses on adjacent segment disease, a major cause of morbidity for patients. The focus of this abstract is the location of adjacent segment disease development after ACDF.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Discuss the impact of number of levels of fusion construct on the development of adjacent segment disease; 2) Identify the likelihood of adjacent segment disease to occur after ACDF.

References: 1. McAfee PC, Cunningham BW, Hayes V, Sidiqi F, Dabbah M, Sefter JC, et al: Biomechanical analysis of rotational motions after disc arthroplasty: implications for patients with adult deformities. Spine (Phila Pa 1976) 31:S152-160, 2006 2. Mummaneni PV, Burkus JK, Haid RW, Traynelis VC, Zdeblick TA: Clinical and radiographic analysis of cervical disc arthroplasty compared with allograft fusion: a randomized controlled clinical trial. J Neurosurg Spine 6:198-209, 2007 3. Murrey D, Janssen M, Delamarter R, Goldstein J, Zigler J, Tay B, et al: Results of the prospective, randomized, controlled multicenter Food and Drug Administration investigational device exemption study of the ProDisc-C total disc replacement versus anterior discectomy and fusion for the treatment of 1-level symptomatic cervical disc disease. Spine J 9:275-286, 2009 4. Nabhan A, Ishak B, Steudel WI, Ramadhan S, Steimer O: Assessment of adjacent-segment mobility after cervical disc replacement versus fusion: RCT with 1 year's results. Eur Spine J 20:934-941, 2011 5. Nunley PD, Jawahar A, Kerr EJ, 3rd, Gordon CJ, Cavanaugh DA, Birdsong EM, et al: Factors affecting the incidence of symptomatic adjacent-level disease in cervical spine after total disc arthroplasty: 2- to 4-year follow-up of 3 prospective randomized trials. Spine (Phila Pa 1976) 37:445-451, 2012 6. Park DH, Ramakrishnan P, Cho TH, Lorenz E, Eck JC, Humphreys SC, et al: Effect of lower two-level anterior cervical fusion on the superior adjacent level. J Neurosurg Spine 7:336-340, 2007