A surgical instrument apparatus (10) includes an elongated alignment rod (11) that can enable a surgeon to define alignment with a patient's long bone. An instrument block body (16) can slide upon the alignment rod (11) between its end portions (12, 13). A locking member forms a connection with the rod at a selected position along the rod. The locking member includes a cam locking arrangement (25) that rotates about a pivot (24) on the instrument body. The cam has a handle portion or arm (28) that enables a user to rotate the cam and its locking tab about its pivot. Part of the locking cam includes a locking tab having a slot (37) that extends circumferentially about ninety degrees around the pivot of the cam. The slot is positioned radially in between the pivot and the periphery of the locking member at a locking member bearing surface. The open end portion (40) of the slot communicates with the locking member periphery.
