Evaluation of bony fusion after anterior cervical discectomy: a systematic literature review and meta-analysis

Significant variability exists in reported fusion rates in the cervical spine after anterior discectomy. Here we review fusion assessment methods, timing of fusion with various intervertebral devices, and examine correlations with clinical outcomes. PubMed, Medline, Embase, Web of Science, Cochrane Library, and Emcare were searched on December 9 2024 for studies involving 1- or 2-level anterior cervical discectomy with quantitative fusion assessment via CT or X-ray. A meta-analysis was conducted using a random-effects model to pool fusion rates and their 95% confidence intervals (CIs) at different follow-up points, for different cage types and different cut-off values evaluating fusion. Sixty-four included studies evaluated 5633 patients. Pooled fusion rates increased over time: 55.6% (95% CI: 43.5%, 67.2%) of patients demonstrated fusion at three months, 74.4% (67.6%, 80.1%) at six months, 88.1% at 12 months (85.1%, 90.6%), and 91.8% (89.1%, 93.9%) at 24 months. Subgroup analysis revealed variation in fusion rates depending on cage type, with titanium cages yielding slightly higher rates at all follow-up times. Sensitivity analysis with fusion criteria showed that a cut-off value < 2 mm for interspinous distance yielded lower fusion rates than the cut-off < 2° for Cobb angle at 6 (70% vs. 77.3%), 12 (83.9% vs. 91.1%) and 24 months (89.5% vs. 91.7%). Results on the correlation between fusion and clinical outcomes were inconsistent. Fusion rates improved over time, approaching 56% at 3 months and 90% at 12 months. Notably, to alleviate heterogeneity across studies, there is a dire need to harmonize reporting guidelines in future research.