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

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.To measure facet distraction using computed tomography (CT) and compare the results with the clinical outcomes after ACDF.Retrospective cohort study.A consecutive series of patients (n = 144) who underwent a single-level ACDF were included.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.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.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.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.