Summer 2005

Articulated Robot Flexes Muscle

Deep in the bowels of San Francisco General Hospital (SFGH), a Motoman UP50 robot, designed to do factory work, is helping UCSF orthopaedic biomechanics researchers learn what happens to a human elbow when it bends at different angles.

Instead of riveting bolts or doing spot welds, the robot — called a six-axis robotic actuator — flexes a cadaver elbow joint as a graduate student under the supervision of Christian Puttlitz, Ph.D., director of the Orthopaedic Biomechanics Laboratory, makes a precise record of its movement.

The biomechanics lab focuses on the orthopaedics issues that appear in the only level 1 trauma center in San Francisco -- "big, difficult fractures," as Puttlitz puts it. "Once a week, I get a faculty member knocking on my door, suggesting an experiment on treating fractures." That is exactly the way it should be, according to Puttlitz.

"It's really a nice situation for performing very clinically relevant biomechanical studies," he says. "I like to look at the etiology, what causes these things to happen. We're starting up quite a few projects on ankle fractures, tibial fractures and pelvis fractures, which are very complicated to treat."

One of the overall themes for the lab is to determine how the mechanical environment of a fracture affects healing. The ends of broken bones generate soft tissue of bone-forming cells. If a fractured bone is stabilized immediately, it heals in one way. If stabilized later, it heals differently. It's possible that the bone-forming cells generated when a fracture is stabilized with an external brace or fixator result in a healed bone less strong than one without external support. Puttlitz and his colleagues are creating computer models to measure the different factors involved in healing under different conditions.

UCSF's biomechanical research at SFGH has had a checkered history. The lab very nearly died when its previous director left in 1999 and the space was turned to other functions. Puttlitz was appointed to restart the lab in late 2002.

Since then, the lab has acquired cellular and molecular biologist Ralph Marcuccio, who is co-director of the SFGH Orthopaedic Research Laboratories, two postdoctoral students, doctoral and master's degree students, medical students and summer undergraduate interns. While the lab has been building a staff and a facility, it also has developed a reputation in industrial and scientific circles.

A recent study published in the "Journal of Bone and Joint Surgery" compared two different screw systems for surgically stabilizing the joint between the spine and the skull. The results made it much easier for surgeons to match each screw system to the surgical needs of individual patients.

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