A deformity in bone is the result of growth abnormalities, trauma, or previous surgery. This results in a crooked bone. 

deformity

The effect of such a deformity is that it causes abnormal loading of the joints in the affected limb, possibly resulting in osteoarthritis. The correction is usually achieved by making an osteotomy (bone cut) and then straightening the limb. The straightening is often achieved through the use of an external fixator device. The procedure is similar to a limb lengthening and the potential risks and recovery are very similar