Bunions may be caused by foot mechanics that result in too much pressure on the big toe (metatarsophalangeal joint). An abnormal foot motion called excessive pronation, having certain foot shapes such as flatfoot, and wearing shoes that squeeze the toes together or shift weight to the toes (such as high-heeled shoes) may all contribute to the pressure. Over time, the constant pressure forces the big toe out of alignment, gradually bending it toward the other toes (displacement).
A bunionette, or tailor's bunion, is one that develops at the base of the little toe. When the long bone that connects to the toe (metatarsal) bends away from the foot, the little toe bends inward and the joint swells or enlarges.
Other factors that can lead to a bunion include:
- Loose ligaments in the foot.
- Previous injury to the foot.
- Hammer toe or removal (amputation) of the second toe. When the joint of the second toe rises, as in hammer toe or the second toe is missing, it becomes easier for the big toe to drift toward the other toes.
- Abnormal development of the foot.