An easily assembled provisional orthopaedic implant having first and second components. The first component may include a stem which can be inserted into an intramedullary canal and may be a femoral component of a knee joint prosthesis. The second component has a body and a sliding retention member. The retention member can be manually engaged with a groove on the stem of the first component to lock the two components together. The second component may form of an intercondylar box and have a projecting tab engageable with a recess on the femoral component to properly orient the two components when they are placed in registry with each other.