Is screw position a greater contributor to adjacent segment disease than plate-to-disc distance following anterior cervical discectomy and fusion?

BACKGROUND

To investigate the risk factors for radiographic adjacent segment disease (RASD), with a focus on the impact of screw position, following anterior cervical discectomy and fusion with plate fixation (ACDF-P).

METHODS

We conducted a comprehensive analysis on 126 patients who underwent ACDF-P for degenerative cervical spinal disease, evaluating various factors such as demographics, cervical sagittal parameters, the number of fused segments, sagittal screw angle, plate to disc distance (PDD), and screw position score (SPS). Based on MRI findings, we classified patients into ASD and Non-ASD groups. Logistic regression analysis was used to evaluate risk factors, and the model's discrimination was assessed using the receiver operating characteristic (ROC) curve. Additionally, we evaluated the predictive value of SPS for RASD using ROC curves. To further investigate the relationship between screw position and RASD, we reanalyzed the data of patients with PDD of less than 5 mm to eliminate the effect of PDD.

RESULTS

Among the 126 patients, 57 developed RASD after a minimum follow-up period of 5 years. No significant differences were observed in demographics, cervical sagittal parameters, number of fused segments, or sagittal screw angle between the two groups (p > 0.05). However, PDD and SPS showed significant differences between the two groups (p < 0.05). Multivariate binary logistic models revealed that PDD (OR: 3.238; 95% CI:1.191-8.807; p < 0.021) and SPS (OR: 1.309 95% CI: 1.092-1.568; p = 0.004) were risk factor for RASD. The models exhibited excellent discrimination and calibration. The area under the curve (AUC) for RASD identified by SPS were 0.674. Among patients with PDD less than 5 mm, SPS was significantly higher in the ASD group compared to the Non-ASD group (p < 0.05). After grouping by screw position, it was determined that both the incidence of RASD (70.5% vs. 34.6%, p < 0.05) and the percentage of long-segment fusion (3-4 levels) (38.6% vs. 7.7%, p < 0.05) were significantly higher in the group with a score greater than 6 compared to the group with a score of 6 or lower.

CONCLUSIONS

Our findings indicate that a PDD of less than 5 mm and a higher SPS are related with RASD following ACDF-P. Secondary analysis indicates that screw position, as indicated by the SPS, may be a primary contributor to ASD, rather than PDD.

CLINICAL TRIAL NUMBER

Not applicable.