A colpotomy system includes a surgical instrument having a cutting element and a receiver at a distal end thereof and a uterine instrument. The uterine instrument has a handle (10) operably coupled to a shaft (45) having a balloon (40) at a distal end thereof, the shaft extending through a retaining member (60) to access a surgical site, the retaining member including a plurality of transmitters (430) for transmitting at least one signal. A distance between the cutting element of the surgical instrument and one end of the retaining member of the uterine instrument is calculated to determine whether the cutting element is within a predetermined operating zone.
