A high-riding vertebral artery (HRVA) is defined as C2 isthmus height ≤ 5 mm or/and internal height ≤ 2 mm measured 3 mm lateral to the border of the spinal canal. Its reported prevalence varies widely. If overlooked approaching craniocervical fusion, injury to vertebral arteries may follow affecting the outcome. The present meta-analysis aims to provide pooled prevalence (PP) of HRVA.
Comprehensive database search was conducted by three researchers. Peer-reviewed studies following strict definition of the HRVA and reporting its prevalence were included. Risk of bias was assessed by means of AQUA tool. PRISMA guidelines were followed. PP was calculated using random-effects model.
20 studies with a total of 3126 subjects (7496 sides) were analyzed. Overall PP of at least one HRVA was 25,3% (95% CI 19,6-31,5). Prevalence in subjects without the most important confounding factor, rheumatoid arthritis (RA), was 20,9% (95% CI 16,5-25,8). Patients with RA had prevalence of 42,9% (95% CI 23,8-63,1). Difference between non-RA and RA was significant (p < 0,001, test of homogeneity, chi-square). No geographical differences were noted (p = 0,20, test of homogeneity, chi-square). Among subjects with HRVA, unilateral HRVA was present in 70,3% (95% CI 65,2-75,2) and bilateral in 29,7% (95% CI 24,8-34,8). There was no left or right side predilection (50,8% [95% CI 33,8-67,6] and 49,2% [95% CI 32,4-66,2], respectively) CONCLUSIONS: Craniocervical fusion should be preceded by examination of vertebral arteries at the level of C2 as HRVA is common and might preclude safe insertion of transarticular or transpedicular screws.

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