A method of preparing an interpositional implant suitable for a knee. The method includes determining a three-dimensional shape of a tibial surface of the knee. An implant is produced having a superior surface and an inferior surface, with the superior surface adapted to be positioned against a femoral condyle of the knee, and the inferior surface adapted to be positioned upon the tibial surface of the knee. The inferior surface conforms to the three-dimensional shape of the tibial surface. The implant may be inserted into the knee without making surgical cuts on the tibial surface. The tibial surface may include cartilage, or cartilage and bone.