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Bone Foot & Ankle

First Metatarsal (Full)

os metatarsale primum

The first metatarsal is the primary weight-bearing metatarsal at toe-off, transmitting 40-60% of forefoot load through the sesamoid complex. Its base articulates with the medial cuneiform at the first TMT joint, the site of Lapidus arthrodesis. Its head is divided into medial and lateral grooves by the intersesamoid crest. The first metatarsal is shortened in Morton's foot and long in hallux rigidus.

Anatomical Data

Structure & Landmarks

Articulations
Landmarks
  • Medial eminence (hallux valgus bump, from medial head expansion)
  • Plantar sesamoid grooves
  • Base (Lapidus fusion site)
OssificationPrimary centre in the shaft at 9 weeks fetal. Distal epiphysis fuses at 18 years.
Clinical Relevance

Clinical Notes

Hallux valgus produces lateral deviation of the great toe and medial deviation of the first metatarsal (metatarsus primus varus). The intermetatarsal angle (between 1st and 2nd metatarsal shafts) and hallux valgus angle (between 1st metatarsal and proximal phalanx) guide surgical correction choice.

Pathology

Common Injuries & Conditions

Hallux Valgus (Bunion)

Medial deviation of the first metatarsal with lateral drift of the big toe, producing a painful medial prominence.

Hallux Rigidus

Osteoarthritis of the first MTP joint with a dorsal osteophyte on the metatarsal head, limiting toe extension.

First Metatarsal Fracture

Usually from direct crush; displaced fractures alter weight-bearing and often need fixation.

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