Accessory carpal bones - Scoping review with meta-analysis: Accessory bones around the scaphoid

Accessory carpal bones around the scaphoid are uncommon anatomical variants that may mimic fractures, non-unions, or other pathological entities on wrist imaging. Despite more than a century of published reports, the literature remains limited by inconsistent terminology, unclear anatomical definitions, and variable reporting quality. This review aimed to synthesize the available evidence on accessory bones around the scaphoid and to clarify their prevalence, anatomical characteristics, imaging features, clinical presentation, and management.

We performed a combined systematic review, prevalence meta-analysis, and scoping review. PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar were searched without date or language restrictions. For the meta-analytic component, original prevalence studies were included; for the scoping component, case reports and case series were additionally evaluated to map anatomy, terminology, imaging findings, symptoms, and treatment.

Eleven studies comprising 27,681 examined limbs were included in the prevalence synthesis, and 60 case reports describing 71 subjects were included in the scoping review. Reported accessory bones around the scaphoid included os centrale carpi, os scaphoideum bipartitum, os radiale externum, os radiostyloideum, os epitrapezium, os scaphocapitatum anterius, and the poorly defined os parascaphoideum. Pooled prevalence estimates for individual entities were uniformly low, generally below 0.1%, with substantial heterogeneity and important methodological limitations related to inconsistent terminology and unclear anatomical criteria. Case reports showed that these variants are usually incidental but may occasionally present with pain, restricted motion, edema, fracture, or diagnostic confusion after trauma. Across the literature, reporting quality was generally low, and anatomical definitions were often insufficient.

Accessory bones around the scaphoid are rare and remain poorly characterized in the literature. A standardized anatomical definition and diagnostic criteria based on standardized imaging are needed to improve future research.