Establishing a relationship using CT between facet distraction and clinical outcomes after ACDF.

Background Context: Anterior cervical discectomy and fusion (ACDF), the gold standard treatment for radiculopathy and myelopathy, has the potential risk of inducing facet-mediated pain through over-distraction. However, the relationship between the clinical outcomes and facet distraction after ACDF remains unclear.

Purpose: To measure facet distraction using computed tomography (CT) and compare the results with the clinical outcomes after ACDF.

Study Design: Retrospective cohort study.

Patient Sample: A consecutive series of patients (n = 144) who underwent a single-level ACDF were included.

Outcome Measures: Interfacet distance on preoperative and postoperative lateral cervical radiographs and CT. Visual analog scale for neck pain (VASn), and arm pain (VASa), neck disability index (NDI), the Short Form 36-item health survey (SF-36) were used for clinical outcomes.

Methods: Each patient underwent plain radiography of the lateral cervical spine preoperatively, immediately and two years postsurgery. CT was performed preoperatively, and at 3 days and 1-year postsurgery. The inter-facet distance was measured at each time point, and changes in values from the preoperative distance were noted and used for study. Patient-reported outcome measures were obtained preoperatively and at 2-year follow-up. Receiver operating characteristic (ROC) curves were generated to derive the critical facet distraction point.

Results: The 3 weeks postoperative VASn score was the most severe and showed a tendency to decrease during the follow-up period. There was a significant positive correlation between the change value of facet distraction measured using CT and 3 weeks postoperative VASn score. ROC curve analysis showed that the cut-off value of Δ facet distraction was 1.8 mm. The over-distraction group (Δ facet distraction ≥1.8 mm, n = 75) showed significantly worse clinical outcomes than the control group (Δ facet distraction <1.8 mm, n = 69), including neck and arm pain VAS scores at all time points until the final 2-year follow-up.

Conclusion: The change value of facet distraction measured using CT rather than plain radiography correlated better with neck pain, and over-distraction contributed to adverse long-term outcomes, including neck and arm pain after ACDF. Additionally, an over-distraction of ≥1.8 mm may cause radiculopathy of adjacent segments along with facet-mediated axial pain; therefore, cage height should be carefully determined to avoid over-distraction during ACDF.