A bunion is a thickened lump at the base of the big toe. It causes the big toe to move toward the smaller toes. It can make walking difficult.

Bunion
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Bunions are caused by a deformity of the metatarsophalangeal (MTP) joint at the base of the big toe. This causes instability of the joint.

Deformity can be caused by:

  • Flat feet, which transfer too much weight to the MTP joint
  • Narrow-toed shoes and high heels
  • Certain neuromuscular diseases, such as cerebral palsy or multiple sclerosis
  • Marfan syndrome
  • Activities that put undue stress on the feet, such as ballet