Unicompartmental replacement instrument and method

The disclosures herein relate generally to surgical instruments and more particularly to an instrument providing for a less invasive unicompartmental replacement procedure. A surgical instrument for establishing and verifying cutting depth and alignment includes a distal saw drill guide, a rod adaptor removably mounted on the distal saw drill guide and a modular alignment rod removably mounted on the rod adaptor. The distal saw drill guide includes pin apertures for receiving a plurality of pins for locating the distal saw drill guide on the distal end of a femur. A distal saw block is mounted on the pins in replacement of the distal saw drill guide the rod adaptor and the alignment rod. A stylus is adjustably attached to a stylus block which is movably mounted on the distal saw block. The rod adaptor and modular alignment rod are movably mounted on the distal saw block in replacement of the stylus and stylus block.