What exactly is computer assisted surgery (CAS)?  Most people are aware of, if not currently using, GPS in their cars.  It tells the driver where he is now and how to get to where he wants to go.  CAS is very similar in concept.  It is a system that tells the surgeon where his hands are in relation to the hip or knee.  It is a tool that aids the surgeon in making more accurate cuts and positioning the implants in the optimal position.  Long term studies will determine whether CAS improves clinical outcomes, and at this time, the data is supportive.