Changes to medical coding systems happen about every ten years, and the newest changes have to be implemented by October of 2013. The new set of codes are not simply an extension of the old ones, but go into more detail and specificity. One of the biggest changes with icd 9 and icd 10 is the coding that will allow medical staff to differentiate left from right when dealing with different parts of the body, and whether the issue is a first occurrence, or a subsequent occurrence.