Accessory Epiphysis (Pseudoepiphysis)

A pseudoepiphysis is an accessory epiphysis that does not significantly contribute to the longitudinal growth of a tubular bone. One or more can occur in the same patient as normal variants, but they have also been associated with Down syndrome and hypothyroidism (~80% of patients with Down syndrome have pseudoepiphyses).

When found incidentally in patients without chromosomal and metabolic abnormalities, they they are most common in the distal thumb metacarpal followed by the proximal index finger metacarpal. In patients with Down syndrome, they are more common in the proximal index finger metacarpal followed by the distal thumb metacarpal (i.e., the order of the two most common sites is reversed).

References

• Freyschmidt J, Brossmann J, Wiens J, Sternberg A. The Hand-General Aspects. In Freyschmidt's Köhler and Zimmer: Borderlands of normal and early pathologic findings in skeletal radiography. Fifth revised edition. Thieme (2003). Pp 23-24.
• Kozin SH and Waters PM. Fractures and dislocations of the hand and carpus in children. In Rockwood and Wilkins' Fractures in Children. Seventh edition. Wolters Kluwer (2010). P 227.
• Ogden JA, Ganey TM, Light TR, Belsole RJ, Greene TL. Ossification and pseudoepiphysis formation in the "nonepiphyseal" end of bones of the hands and feet. Skeletal Radiol. 1994 Jan;23(1):3-13.