A UC Davis student's invention that models human joints with unprecedented precision will be highlighted Tuesday, Nov. 18, at the annual meeting of the American Society of Mechanical Engineers in Dallas.Doctoral student Tammy Haut set out to improve the computer models used by sports-medicine specialists to study how joint injuries occur and how best to repair them."The existing methods for generating models of the knee, shoulder and hip, such as MRI and CT scans, are either inaccurate or very difficult to set up and use," Haut says. They need to be accurate to within 20 microns -- about half the thickness of a piece of paper -- but none comes closer than 90 microns.With her faculty adviser, UC Davis engineering professor Maury Hull, and a military orthopedic surgeon, Stephen Howell of Travis Air Force Base, Haut devised a new approach.Called a three-dimensional coordinate digitizing system, it uses a non-destructive laser, a computer-controlled tabletop and a commercial software program to map the surface of a cadaver joint. The 3-D computer images it produces meet the 20-micron goal, Haut says.Haut and five other finalists will present their work Tuesday morning in a national student competition held by the engineering society's bioengineering division. In 1995, Haut won honorable mention in a similar contest for bachelor's-degree students.