A surgical drill bit and retrograde reamer bit perform antegrade and retrograde drilling of a stepped diameter surgical tunnel employing a detachable reamer bit of a different diameter than the entry (antegrade) bit. The entry drill bit employs a cannulated shaft having a bore adapted to receive a guidewire and fluted cutting edges on an outer circumference of the shaft to define the surgical tunnel. A transverse receptacle across a diameter of the shaft extends substantially orthogonal to an axis of the bore is adapted to receive a reamer bit having a wider diameter for antegrade drilling the larger of the stepped diameters by withdrawing the reamer bit in the opposed direction from entry. The transverse receptacle is shaped for receiving the reamer bit and is adapted to secure the bit for retrograde cutting by intersecting with the bore for securing the reamer bit via engagement of a guidewire.
