Abstract: An expandable acetabular reaming system for use in hip replacement surgery comprises a reamer head having a convex forward surface attached to a base plate that defines an interior space therebetween. The forward surface includes a plurality of apertures therethrough. The base plate includes a central aperture over which a flexible bladder is mounted within the interior space. The reaming system further includes a plurality of cutting blades mounted to the bladder and positioned so as to correspond with respective apertures. An air cylinder is coupled to the underside of the base plate and includes an open top in communication with the bladder through the central aperture of the base plate. A threaded shaft extends through a threaded aperture in a bottom wall of the air cylinder and is coupled to a thimble-type knob. As a user turns the knob, the shaft rotates to force air through the base plate aperture so as to inflate the bladder.