A patient support apparatus for supporting a patient in a prone position during a surgical procedure is provided, including an open fixed frame suspended above a floor and a pair of spaced opposed radially sliding joints cooperating with the frame, each joint including a virtual pivot point and an arc of motion spaced from the virtual pivot point, the joints being movable along the arc providing a pivot ship mechanism for a pair of pelvic pads attached to the joints. A base for supporting and suspending a patient support structure above the floor, for supporting a patient during a surgical procedure, the base including a pair of spaced opposed vertical translation subassemblies reversibly attachable to a patient support structure, a cross-bar, and a rotation subassembly having two degrees of rotational freedom; wherein a location of each vertical translation subassembly is substantially constant during operation of the patient support structure.