The vertebral artery loops: a systematic review and meta-analysis.

purposeVertebral artery loops (VALs) are focal deviations of the vertebral artery course that may produce pulsatile nerve-root compression and substantially increase the risk of iatrogenic vascular injury during cervical spine procedures. Although individually uncommon, they are a recognised "hidden danger" whose recognition changes preoperative planning. We aimed to estimate the pooled prevalence of VALs, to explain the wide variation in reported figures, and to translate these data into a practical framework for preoperative decision-making in cervical spine surgery.

methodsA PRISMA-guided systematic search of PubMed, Web of Science, and Google Scholar identified 58 publications for qualitative synthesis. Ten primary studies reporting the number of examined vertebral arteries (VAs) and identified loops were pooled in a meta-analysis of proportions. A DerSimonian-Laird random-effects model was applied to raw proportions; a Freeman-Tukey double arcsine (DAS) transformation was used as a variance-stabilising sensitivity analysis. Heterogeneity was assessed with Cochran's Q and I², and explored with a pre-specified subgroup analysis by study methodology (radiological imaging cohorts vs. anatomical/morphometric series).

resultsTen studies comprising 7,475 VAs and 126 loops were pooled. The random-effects prevalence of VALs was 1.71% (95% CI 0.87%-2.55%), with substantial heterogeneity (I² = 93.4%; Q = 136.9; p < 0.0001). Subgroup analysis showed that this heterogeneity is largely methodological: radiological imaging cohorts pooled at 1.09% (95% CI 0.60%-1.58%; I² = 82%), whereas the two small anatomical/morphometric series - which were also the two statistical outliers - pooled at approximately 39%. After removing these two studies, the raw-proportion (1.09%) and Freeman-Tukey (1.19%) estimates converged, confirming a robust prevalence of roughly 1-2% in unselected radiological populations. Clinically relevant loops were most often located in the V2 segment at mid-cervical levels (C4-C6); medial loops were associated with vertebral body scalloping and enlargement of the foramen transversarium, and lateral/foraminal loops with cervical radiculopathy.

conclusionVALs are uncommon but disproportionately dangerous. The pooled prevalence is best understood not as a population statistic but as a baseline pre-test probability that indirect osseous signs sharply raise. When vertebral body scalloping, an enlarged foramen transversarium, or anomalous (non-C6) entry is seen - or when complex anterior decompression or craniovertebral instrumentation is planned - preoperative CTA/MRA and a deliberate modification of the operative corridor are warranted.