What are the causes of bunion deformity? Bunions are a progressive deformity commonly thought of as just a bump. Bunions are so much more, bunions are actually complex tri planar deformities caused by an unstable joint that allows the first metatarsal to lean, elevate and rotate out of alignment. There are risk factors for development of bunion deformity, and these include family history or genetic predisposition for the structure and shape of a foot more likely to develop bunion deformity, wearing shoes that crowd the toes and inflammatory conditions such as rheumatoid arthritis. The presence of a bunion can make wearing certain shoes and performing activity painful and difficult due to the progressive nature of bunion deformities. Over time, additional symptoms may develop including arthritis, calluses, crossing over of the big toe or the second toe hammer, toes, bone spurs, and pain to the ball of the foot.