Prevalence and clinical implications of median nerve variants within the carpal tunnel: a systematic review and meta-analysis

• Median nerve variants within the carpal tunnel have a pooled prevalence of 12%. • Bifid median nerve is the most frequently reported morphological variant. • No consistent association was found between anatomical variants and carpal tunnel syndrome. • Coexisting vascular or muscular anomalies may influence surgical complexity. • Preoperative imaging may aid anatomical identification, although clinical benefit remains uncertain. Anatomical variants of the median nerve (MN) within the carpal tunnel are clinically relevant due to their potential impact on the development, diagnosis, and surgical management of carpal tunnel syndrome (CTS). Reported prevalence estimates vary considerably across populations and study designs. To systematically review the literature and estimate the pooled prevalence of morphological variants of the median nerve within the carpal tunnel, and to assess their laterality, geographic distribution, and reported clinical implications. A systematic review and meta-analysis were conducted in accordance with PRISMA 2020 guidelines. MEDLINE, Scopus, Web of Science, CINAHL, and LILACS were searched from inception to November 2024. Google Scholar was used for supplementary screening of gray literature. Observational studies reporting the prevalence of MN variants identified through imaging, surgical exploration, or anatomical dissection were included. Methodological quality was assessed using the Anatomical Quality Assessment (AQUA) tool. Pooled prevalence estimates were calculated using a random-effects model (DerSimonian–Laird) with Freeman–Tukey double arcsine transformation. Sixty-three studies met eligibility criteria for qualitative synthesis, and 19 studies (n = 9,045 subjects) were included in the primary meta-analysis. The pooled prevalence of MN variants within the carpal tunnel was 12% (95% CI: 9–15%), with substantial heterogeneity (I² = 87%). Subgroup analysis showed similar prevalence in imaging-based studies (12%, 95% CI: 9–15%; I² = 87.8%). No clear laterality predominance was observed (right: 46%, 95% CI: 40–52%; I² = 0.0%; left: 53%, 95% CI: 48–59%; I² = 0.0%), whereas bilateral presentation demonstrated greater variability (21%, 95% CI: 6–36%; I² = 90.6%). Geographic subgroup analysis showed pooled prevalence estimates of 22% in Asia (95% CI: 13–31%; I² = 92.6%), 20% in Europe (95% CI: 14–27%; I² = 79.2%), and 18% in America (95% CI: 16–20%; I² = 19.4%). Morphological variants of the median nerve within the carpal tunnel are relatively common anatomical findings. Current evidence does not support their role as independent risk factors for CTS; however, their coexistence with vascular or muscular anomalies may influence local anatomical relationships and surgical complexity. Preoperative imaging may facilitate anatomical identification and surgical planning, although its impact on clinical outcomes and intraoperative complications remains uncertain and requires further prospective investigation.