A bone fixation plate assembly includes a proximal plate having a proximal body with a first arm projecting therefrom, the first arm having an elongated expansion slot extending through a portion thereof and a threaded bore formed thereon so as to communicate with the expansion slot. A set screw is received within the threaded bore and has a top surface with a driver engaging feature formed thereon and an encircling perimeter edge. A distal plate has a distal body with a first sleeve projecting therefrom. The first sleeve bounds a socket with the first arm received therein. An access opening is formed on the first sleeve and is configured so that the driver engaging feature of the set screw is accessible through the access opening while at least a portion of the perimeter edge of the set screw is covered by the first sleeve.