A method and a device are for determining the compatibility between an adapter, which is to be inserted into a third-party joint ball type to be replaced, and an outer cone of a prosthesis shaft of a modular joint prosthesis, which is inserted in the femur during revision surgery. A test body of a set of test bodies having various inner cones, comprising a marker and a length measuring scale, is fitted onto the outer cone of the shaft of the joint prosthesis and, subsequently, the adapter fitting on the outer cone of the joint prosthesis is determined by successively testing the inner cones for compliance with an admissible minimum distance between the front faces of the outer cone of the shaft of the joint prosthesis and the inner cone and for compliance with an admissible predefined insertion depth of the outer cone of the shaft of the joint prosthesis in the inner cone of the test body.
