Review Question - QID 219580

Placement of the anterior cervical plate in ACDF constructs less than 5mm from the supra-adjacent disc space is a risk factor for adjacent segment ossification (Answer 3).

Numerous factors can influence the development of adjacent segment ossification (ASO). For instance, a start point of the proximal screws near the inferior end plate of the most proximal vertebral body in the fusion construct can act to mitigate cranially-based plate placement within 5mm of the supra-adjacent disc and decrease the risk of ASO.

Huang et al. completed a retrospective case-control study investigating ASO rates in ACDF patients with and without anterior cervical plates. Results show a higher ASO rate in the plate group (29%) compared to standalone (2.8%), with plate-to-disc distance (PDD) <5 mm significantly associated with ASO. Ultimately, they concluded that utilizing standalone cages or plates with >5 mm distance from adjacent discs may minimize ALOD risk.

Kim et al. completed a systematic review of 5 studies assessing the risk of adjacent-level ossification development (ALOD) after ACDF. They found that the incidence of ALOD status post ACDF ranged from 41% to 64%, whereas with total disc replacement, it ranged from 6% to 24%. ALOD was twice as likely to develop at the cranial adjacent segment. Key risk factors included instrumentation use and plate-to-disc distance, with surgical procedure type (corpectomy vs. discectomy and fusion) showing near significance.

Yang et al. performed a retrospective case-control study analyzing the association between PDD, ALOD, and adjacent segment degeneration (ASD). They found that ossification occurred in 61% of cranial adjacent disc spaces and 24% of caudal adjacent disc spaces (P < 0.01). Mean cranial PDD was shorter than caudal PDD (P < 0.01). No significant differences in symptomatic and asymptomatic adjacent segment degeneration were observed among the groups.

Figure A: Demonstrates AP and lateral radiograph status post C4-C6 ACDF with PEEK interbodies.

Incorrect Answers:
Answer 1: Utilization of PEEK interbody devices with cancellous allograft has not been associated with the development of ASO.
Answer 2: The screw start point about the inferior end-plate of the most proximal vertebral body within the ACDF construct is actually associated with lower chances of developing ASO as this positions the plate >5mm from the supra-adjacent disc space.
Answer 4: Positioning the anterior cervical plate >5mm from the adjacent disc space is associated with lower rates of ASO. Also, ASO is less likely to occur at the caudal aspect of the construct.
Answer 5: Coronal malalignment has not been associated with the development of ASO.