Parents will notice a bony hard swelling near the knee joint or at the back near the wing bone. There may be associated deformity in the legs or hand. It arises from the growing part of the bone. Normal cells instead of growing along the length of the bone start behaving abnormally and cause a localised swelling, the swelling will continue to grow till the child is growing. The swelling is benign in nature and does not grow very fast. It needs to be removed if it is big or causing difficulty in moving or using a limb.