US Patent 7090677 Surgical milling instrument for shaping a bone cavity

A mill guide instrument for guiding a tissue cutting tool is provided that is made up of subassemblies of a guide body and a mill guide. The guide body has a distal section dimensioned to fit into a bore in bone and a removable template with a guide surface unique to a proposed cavity shape. The mill guide is connected to the guide body and provides for controlled relative motion between the mill and the guide body. The mill guide has an attached stylus that follows the guide surface of the template. The stylus follows the template guide surface so as to constrain the path of the mill to a preferred milling path.