Accessory Bones of the Hand and Wrist

Description

The posteroanterior X-ray films of the index (A) and little fingers (B) both demonstrate two sesamoid bones (arrows) at the metacarpophalangeal (MCP) joints

Schematic illustration of dorsal aspect of the right hand, showing the accessory ossicles of the wrist. Palmar-located accessory ossicles are shown in broken outline. (1: Os trapezium secundarium, 2: Os paratrapezium, 3: Os praetrapezium, 4: Os epitrapezium, 5: Os trapezoideum secundarium, 6: Os styloideum, 7: Os capitatum secundarium, 8: Os centrale carpi, 9: Os hamuli proprium, 10: Os gruberi, 11: Os vesalianum manus, 12: Os radiale externum, 13: Os epilunatum, 14: Os hypolunatum, 15: Os hypotriquetrum, 16: Os epitriquetrum, 17: Os pisiforme secundarium, 18: Os ulnare externum, 19: Os triangulare, 20: Os ulnostyloideum)

Incidence of accessory ossicles

Sesamoid bones of the hand

Introduction

• Sesamoid bones are small, ovoid shaped bones that can vary in shape/size
  • First defined by Galen, who compared them to seeds
• Accessory ossicles are commonly seen on plain radiographs

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Sesamoid Bones

Thumb Sesamoids

• Two or three sesamoid bones are typically present in the thumb
• Two are always present at the metacarpophalangeal joint
• One is present at the interphalangeal joint in 60-80% of individuals

Sesamoids of Fingers 2-4

• Incidence at the Metacarpophalangeal Joints
  • II: 61%
  • III: 3.9%
  • IV: 1.3%
  • V: 59.5%
• Incidence at the Interphalangeal Joints
  • II: rare
  • III: rare
  • IV: rare
  • V: rare

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Accessory Ossicles of the Wrist

General

• Commonly seen on plain radiographs and cross sectional imaging
• More than 20 were originally described, however many exist

Common Ossicles

• Lunula: between TFCC, triquetrum
• Os Styloideum: on dorsal surface of 2nd or 3rd metacarpal bases, sometimes called carpal boss
• Os Triangulare: just distal to ulnar fovea
• Trapezium Secundarium: volar, medial to tubercle of trapezium
• Os Epilunate: dorsal to lunate
• Os Hamuli Proprium: at tip of hamate hook

Distal Row of Ossicles

• Os Vesalianum Carpi
• Os Ulnare Externum
• Os Hamuli Proprium
• Secondary Capitate
• Gruber Ossicle
• Os Styloideum
• Secondary Trapezoid
• Trapezium Secondarium
• Os Paratrapezium

Ossicles around the Scaphoid

• Paranavicular
• Os Radiostyloideum (persistent radial styloid)
• Os Radiale Externum
• Epitrapezium
• Os Centrale Carpi

Ossicles around the Lunate

• Os Hypolunatum
• Os Epilunatum
• Epipyramis
• Accessory bone between lunate and triquetrum
• Lunula
• Os Triangulare
• Persistent Ulnar Styloid
• Small bony element at the radioulnar joint

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Clinical Significance

• Needs to be updated

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See Also

• Hand And Wrist Anatomy
• Physical Exam Hand
• Hand Pain Main
• Wrist Pain Main
• Finger Pain Main
• Accessory Bones Main

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