<p>A hemi-arthroplasty implant (11) joint replacement for the base of the first metacarpal of the CMC joint is created which can effectively restore and reestablish functional joint mechanics. The implant (11) has a unique head section (13) creating a particular interrelation between a spherical head articular surface (19), that is received in a surgically prepared cavity in the trapezium, wherein a supporting neck (21) in a re-entrant region joins the head to a flat, generally oblong collar (15).</p>
