Bunion after surgery. Coloured X-ray of the foot of a 68-year-old patient showing alignment pins (thin, light) inserted in the toes to correct the deformation caused by a bunion (hallux valgus). A bunion is a swelling of the joint between the big toe and the first metatarsal bone. It causes the base of the big toe to project outwards and the tip of it to point inwards and in extreme cases (as here) can cause the whole foot to become deformed. Bunions are caused by the rubbing of ill-fitting shoes.