Bunion operation cast. Close-up of a foot with a plaster cast around it after an operation to remove a bunion. Bunions are painful, fluid filled pads at the base of the big toe. They are generally caused by a hallux valgus, a deformity in which the big toe joint projects out from the foot, and the toe itself points inwards. This is commonly caused by wearing shoes which are too tight, or more rarely by an inherited weakness of the joint. Small bunions can be corrected with well-fitted shoes and a special pad, but large bunions must be surgically removed. In severe cases, an osteotomy is performed, where the bones of the toe joint are cut and repositioned.