A deformity is a part of someone's body which is not the normal shape because of injury or illness, or because they were born this way. An osteotomy is a surgical operation whereby a bone is cut to shorten or lengthen it or to change its alignment. It is sometimes performed to correct a hallux valgus or to straighten a bone that has healed crookedly following a fracture. It is also used to correct a coxa vera, genu valgus, and genu varum. The operation is done under a general anaesthetic.