Abstract: A joint replacement in situ gauge system enables a surgeon to measure the appropriate spacing between the two sides of a joint, a convex component and a concave component. A replacement in situ gauge system includes a gauge component to measure the pressure and/or displacement of one joint component with respect to the mating component. A gauge component utilizes a displacement device that displaces the convex or concave component to determine a proper spacing for an implant component. The displacement component may be a bladder that is inflated with a fluid and a gauge may measure the pressure of the bladder through a range of motion. A scale may be used to measure physical displacement. The gauge component may be configured in the convex and/or concave components of the system. The gauge component may be removed and then an implant component may be implanted.