US Patent 6,004,323
United States Patent and Trademark Office
University of Iowa Research Foundation (Iowa City, IA, US)
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.
Park, Joon B.; Goel, Vijay K.; Pope, Malcolm H.; and Weinstein, James N. Surgically implantable fastening system. US Patent 6,004,323 filed February 04, 1997 and issued December 21, 1999. https://ir.uiowa.edu/patents/232