Permanent magnets are implanted in bone to unload compressive forces at joints using the repulsive force therebetween. A porous metal container is implanted first and becomes fixed in place by bone growth. The permanent magnet is then inserted in the container and retained in place. A magnet prescription system includes a display and input device which enables a user to alter parameters such as magnet size, strength and placement and calculate and display the repulsive force that will result.