Supraclavicular Foramina in Dry Clavicles: An Observational Study and Meta-Analysis of Prevalence and Laterality

Background/Objectives: The supraclavicular foramen (SCF) is a rare anatomical variant formed when a branch of the supraclavicular nerve traverses the clavicle through a complete transclavicular canal. Published studies differ substantially in study material, denominators, and reporting of side-specific and bilateral data, so bilateral anatomy is often synthesized as if pairing were irrelevant. This study aimed to describe SCF in a Greek osteological sample and to apply a meta-analytic framework distinguishing per-clavicle prevalence, marginal laterality, paired laterality, and separately observed bilateral prevalence. Methods: We examined 115 dry clavicles of Greek origin for SCF frequency, size, and topography. Measurements were obtained independently by two observers using stainless-steel wires and digital calipers, with inter-rater agreement assessed by intraclass correlation coefficients. A systematic review and meta-analysis were then conducted according to PRISMA 2020. Quantitative synthesis included pooled per-clavicle prevalence, conventional marginal left-versus-right comparison, and feasibility-based paired laterality analysis under explicit dependence assumptions when bilateral information was incomplete. Observed bilateral prevalence was analyzed separately using only studies with directly reported body-level bilateral counts. Study quality was assessed using AQUA and CATAM. Results: Complete transclavicular canals, identified by paired supraclavicular foramina representing entrance and exit openings, were present in 3/115 clavicles (2.4%), with a mean patency diameter of 1.5 ± 0.8 mm and a mean relative acromial position of 0.44 ± 0.12. Inter-rater reliability was excellent. Pooled per-clavicle prevalence was 2.2% (95% CI: 1.4–3.0%; I² = 71%). Conventional marginal laterality showed significant left-sided predominance (OR = 1.76, 95% CI: 1.16–2.66; I² = 0%), while feasibility-based paired laterality yielded a stronger effect (paired OR = 2.26, 95% CI: 1.30–3.94). The main observed bilateral-prevalence model yielded 0.95% (95% CI: 0.33–2.70%). Minor small-study effects were suggested by the Doi/LFK framework. Conclusions: SCF is an uncommon developmental variant with consistent left-sided predominance. Bilateral anatomical variants should not be synthesized as if all observations were unpaired; separating per-clavicle prevalence, marginal laterality, paired laterality, and observed bilateral prevalence provides a more transparent and biologically meaningful synthesis.