A bunion is a thickened lump at the base of the big toe. It is the result of the movement of the base of the big toe away from the smaller toes. At the same time, the top of the big toe moves toward the smaller toes. This instability creates metatarsophalangeal (MTP) joint inflammation and bursitis at the base of the big toe.

Bunion
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The exact cause of bunions is unknown, but it is likely a combination of genetics and environmental factors.