Also called scaphoid. Irregular short bone, anterior to head of the talus.
Posterior surface is concave (for articulation of head of talus); anterior surface has 3 triangular areas (separated by 2 faint ridges) for articulation with 3 cuneiforms.
Plantar surface is narrow and rough – for attachment of ligaments and muscles
Medial tuberosity is principal attachment of the tibialis posterior tendon.
Os navicularis or accessory navicular or os tibiale occurs in up to 10% - many variations in shape and position.
Ossification: - usually from one primary centre – appears at 3 yrs
- may have secondary centre at tuberosity – may fuse or remain as secondary bone (accessory navicular or os tibiale externum) (do not confuse with sesamoid bone in tendon)