Adjacent Level Ossification Development Following Anterior Cervical Fusion: How Does it Affect the Next Level Disc?
Academic Article
Overview
abstract
STUDY DESIGN: Retrospective matched cohort analysis. OBJECTIVE: The aim of this study was to investigate the impact of adjacent level ossification development (ALOD) on the affected as well as the next-level discs with regards to range of motion (ROM) and degenerative changes. SUMMARY OF BACKGROUND DATA: Although ALOD is not a rare condition in patients who undergo anterior cervical fusion procedures, there has been little discussion to date about its clinical implications. METHODS: Patients who underwent anterior cervical instrumented fusion with a minimum 2-year follow-up were reviewed. Twelve patients with each respective ossification grade (totally 48 patients) were matched based on age, sex, and number of fusion levels. On the preoperative and final follow-up x-rays, disc height, osteophytes, ROM, and maximal listhesis were assessed at the segments which were one- (the adjacent segment) and two-level cranial (the next segment) to the uppermost fused disc. Then, the patients were divided into two groups according to ALOD degree: group 1 (grade 0-1, N = 24) versus group 2 (grade 2-3, N = 24). The changes of all variables were compared between the two groups. RESULTS: The mean ROM of the adjacent segment increased by 3.6 degree in group 1 and conversely decreased by 2.8 degree in group 2 (P = 0.002). The mean ROM increase of the next segment was significantly greater in group 2 than in group 1 (4.5 vs. 1.2 degree, P = 0.016). The osteophyte growth and the progression of listhesis at the next segment were significantly greater in group 2 (P < 0.05). Disc height of the next segment significantly decreased in group 2, but did not change in group 1. CONCLUSION: Severe ALOD (grade 2-3) following anterior cervical fusion significantly reduced ROM at the affected segment and conversely increased motion at the next segment. This increased motion probably accelerated the degeneration of the next-level disc. LEVEL OF EVIDENCE: 3.
