Objective: There is currently no consensus on whether adjacent-segment degeneration (ASD), loss of disc height (DH), and loss of sagittal segmental angle (SSA) are due to anterior cervical discectomy and fusion (ACDF). The purpose of the present study was to assess the grade of segmental degeneration after ACDF and to analyze if there is a difference with respect to clinical outcome, diagnosis, and number of operated levels.
Methods: A total of 102 patients who underwent ACDF with a minimum follow-up of 18 years were retrospectively identified. At final follow-up, the clinical outcome according to Odom's criteria, the Neck Disability Index (NDI), and reoperation for symptomatic ASD (sASD) was assessed. MRI was performed, and DH, SSA, and the segmental degeneration index (SDI, a 5-step grading system that includes disc signal intensity, anterior and posterior disc protrusion, narrowing of the disc space, and foraminal stenosis) were assessed for evaluation of the 2 adjacent and 4 adjoining segments to the ACDF. MRI findings were compared with respect to clinical outcome (NDI: 0%-20% vs > 20%; Odom's criteria: success vs no success), reoperation for sASD, initial diagnosis (cervical disc herniation [CDH] vs cervical spondylotic myelopathy [CSM] and spondylosis), and the number of operated levels (1 vs 2-4 levels).
Results: The mean follow-up was 25 years (range 18-45 years), and the diagnosis was CDH in 74.5% of patients and CSM/spondylosis in 25.5%. At follow-up, the mean NDI was 12.4% (range 0%-36%), the clinical success rate was 87.3%, and the reoperation rate for sASD was 15.7%. For SDI, no significant differences were seen with respect to NDI, Odom's criteria, and sASD. Patients diagnosed with CDH had significantly more degeneration at the adjacent segments (cranial, p = 0.015; caudal, p = 0.017). Patients with a 2- to 4-level procedure had less degeneration at the caudal adjacent (p = 0.011) and proximal adjoining (p = 0.019) segments. Aside from a significantly lower DH at the proximal cranial adjoining segment in cases of CSM/spondylosis and without clinical success, no further differences were noted. The degree of SSA was not significantly different with respect to clinical outcome.
Conclusions: No significant differences were seen in the SDI grade and SSA with respect to clinical outcome. The SDI is higher after single-level ACDF and with the diagnosis of CDH. The DH was negligibly different with respect to clinical outcome, diagnosis, and number of operated levels.
Keywords: ACDF; MRI; adjacent segment; anterior cervical discectomy and fusion; cervical spine; clinical outcome; degeneration; degenerative; long-term follow-up.