Abstract
BACKGROUND: Trapezium typically maintains consistent morphology, and its anatomical variants are rare. We present the first known familial cases of multiple accessory carpal bones, including bipartite trapezium, and a previously undescribed volar accessory carpal bone located between the scaphoid and capitate. CASE PRESENTATION: A 69-year-old woman was evaluated for a distal radius fracture. Further X-ray and CT imaging revealed a bilateral bipartite trapezium, bilateral os styloideum, os hamuli proprium all having smooth margins and regular cortico-medullar ratio. Cystic changes in the capitate, alongside abnormal morphology of the scaphoid and capitate were also present. Conservative treatment led to full recovery. Upon follow-up, the patient's daughter, reporting wrist clicking but no pain, underwent X-ray and CT imaging, which showed bilateral bipartite trapezium and a right os styloideum. Notably, a novel accessory bone was identified volarly between the scaphoid and capitate in the left wrist. Both cases were congenital and asymptomatic apart from mechanical clicking. None of the patients had associated anomalies. CONCLUSION: These cases represent the first familial report of a bipartite trapezium and introduce a previously unreported volar accessory carpal bone, for which we propose the term os scaphocapitatum anterius. Awareness of such variants is crucial for accurate radiological interpretation and appropriate surgical planning, particularly in cases of trauma or CMC joint pathology, when such variants might be confused with fracture. Advanced imaging modalities such as CT are recommended to confirm morphology and distinguish congenital variants from post-traumatic changes.