Does Two-level Hybrid Surgery Promote Early Fusion Compared with Two-level Anterior Cervical Discectomy and Fusion?

Background context: Hybrid surgery (HS), which involves both anterior cervical discectomy and fusion (ACDF) and cervical disc replacement (ACDR), is increasingly used to treat multilevel cervical disc degenerative disease, yielding satisfactory clinical outcomes. Early fusion is critical after anterior cervical fusion surgeries, but there are no studies comparing the rate of early fusion of HS with that of ACDF.

Purpose: The purpose of this study was to compare the rate of early fusion (3-6 months postoperatively) of two-level HS with that of two-level ACDF surgery.

Study design: The fusion statuses of consecutive patients who underwent two-level ACDF were compared with those of consecutive patients who underwent HS, which involves both ACDF and ACDR.

Patient sample: The study included 860 patients who underwent two-level ACDF or HS for CDDD. After the patients who did not meet the study criteria were excluded, 376 patients were included (165 males, 211 females).

Outcome measures: Radiographic measures included fusion rate of the ACDF level. Self-report measures included visual analog scale (VAS) neck, VAS arm, neck disability index (NDI), satisfaction with the surgery and other symptoms reported by patients during the follow-ups.

Methods: Eight hundred sixty patients who underwent two-level ACDF or HS for cervical disc degenerative disease between January 2015 and January 2023 at our hospital were screened. After excluding the patients who did not meet the study criteria, 376 patients were included (165 males, 211 females). The patients who underwent dual-segment ACDF were categorized into the ACDF-ACDF (FF) group (n=205), while those who underwent dual-segment HS were divided into the ACDF-ACDR (FR) group (n=82) and the ACDR-ACDF (RF) group (n=89) on the basis of the relative positions of the segments selected for ACDF and ACDR. The fusion rates of the segments subjected to ACDF and the clinical outcomes, including the neck VAS score, arm VAS score, NDI score, and other complications, were compared among the three groups at 3 months, 6 months, and 1 year postoperatively. Fusion was defined as the formation of a continuous bone bridge in the target fusion area, as observed on three-dimensional computed tomography (CT) images.

Results: The average age of the patients in the FF group was higher than that of the patients in the FR and RF groups (p<0.001). At 3 months postoperatively, the fusion rate was 70.7% (58/82) in the FR group, 39.5% (162/410) in the FF group, and 42.7% (78/89)in the RF group (P<0.001). At 6 months postoperatively, the fusion rate was 74.6% (306/410) in the FF group, 91.5% (75/82) in the FR group, and 87.6% (78/89) in the RF group (P<0.001). At 1 year postoperatively, the fusion rate was 91.9% (377/410) in the FF group, 98.8% (81/82) in the FR group, and 100% (89/89) in the RF group (P=0.002). At 3 months postoperatively, the fusion rate was higher in the FR group than in the FF group (70.7% vs. 45.4%) (P<0.001). At 6 months postoperatively, the fusion rate of the distal segment was higher in the RF group than in the FF group (87.6% vs. 66.3%). In the FF group, the fusion rate in the proximal segment was higher than that in the distal segment at 3, 6, and 12 months postoperatively. One year after surgery, 15 segments-3 proximal and 12 distal-in the FF group developed pseudoarthrosis. Compared with the other two groups, the FR group had lower neck VAS scores at 3 months postoperatively and a lower rate of dizziness complaints during the 1-year follow-up period. There were no statistically significant differences in the remaining clinical outcomes.

Conclusions: The early fusion rate after two-level HS was higher than that after two-level ACDF. The early fusion rate of two-level HS was higher in the FR group than in the RF group. For two-level ACDF, the early fusion rate was higher in the proximal segment than in the distal segment. Additional biomechanical studies are needed to explore the biomechanical differences in fusion levels between HS and multilevel ACDF.