The present invention discloses a nut to be used in a spinal screw and plate assembly to affix the screw and plate assembly to the spinal bone. The nut has a polymer insert that when contacted with a screw allows a bone plate and screw structure to relax over time....http://www.google.fr/patents/US6004323?utm_source=gb-gplus-shareBrevet US6004323 - Surgically implantable fastening system
