Bunion before (left) and after (right) surgery, coloured X-rays. A bunion is a deformity of the big toe, often caused by pressure from ill-fitting shoes. In this bunion, the first metatarsal (the bone in the sole beneath the big toe) is compacted into the second metatarsal (to its left). Surgical treatment can correct this, as seen at right, where the bones are more evenly spaced. After surgery the foot must be immobilised for up to two months to allow the bones and muscles to set in their new position.