A multimode instrument assembly (10, 11) configurable for performing a dermatotomy in a percutaneous procedure and further configurable for performing cuts in open surgery includes a pointed blade (68) and a hollow sheath body (18, 200) disposed to encapsulate the pointed blade (68) inside a longitudinal instrument cavity (32) to protect a user. The hollow sheath body (18, 200) is supported for longitudinal translation with respect to the blade (68). The hollow sheath (18) may be positioned and locked at a first position to completely encapsulate the blade (68) inside the instrument cavity (32) for safe handling. Otherwise the hollow sheath body (18, 200) is movable to second and third positions with different lengths of the blade extending out through a front face (23) of the hollow sheath body (18, 200). A compression spring biases the hollow sheath body (18) toward the first safety position. The multimode instrument is primarily intended for making a precise pierce cut with a consistent cut depth and cut length.
