By: 18 February 2015

Engineers at Oregon State University (OSU) have developed and successfully demonstrated the value of a simple pulley mechanism to improve hand function after surgery

The device, tested in cadaver hands, is one of the first instruments created that could improve the transmission of mechanical forces and movement while implanted inside the body.

The technology may offer new options to people who have lost the use of their hands due to nerve trauma, and could ultimately be expanded to improve function of a wide range of damaged joints in the human body.

“This technology is definitely going to work, and it will merge artificial mechanisms with biological hand function,” said Ravi Balasubramanian, an expert in robotics, biomechanics and human control systems, and assistant professor in the OSU College of Engineering.

“We’ll still need a few years to develop biocompatible materials, coatings to prevent fibrosis, make other needed advances and then test the systems in animals and humans,” Balasubramanian said. “But working at first with hands – and then later with other damaged joints such as knees or ankles – we will help people recover the function they’ve lost due to illness or injury.”

Initially, the OSU research will offer a significant improvement on surgery now used to help restore the gripping capability of hands following nerve damage. Tendon-transfer surgery for high median-ulnar palsy essentially reattaches finger tendons to a muscle that still works. But the hand function remains significantly impaired, requiring a large amount of force, the stretching of tendons, and fingers that all move at the same time, instead of separately as is often needed to grasp an object.

The new mechanism developed at OSU is not really robotic since it has no sensory, electronic or motor capabilities, said Balasubramanian. Rather, it’s a passive technology using a basic pulley that will be implanted within a person’s hand to allow more natural grasping function with less use of muscle energy.

The new research showed, in cadavers, how the mechanism can produce more natural and adaptive flexion of the fingers in grasping. The force needed to close all four fingers around an object was reduced by 45 per cent, and the grasp improvement on an object reduced slippage by 52 per cent.

“There’s a lot we may be able to do,” said Balasubramanian, speaking about the long-term potential of such mechanised assistance. “Thousands of people now have knee replacements, for instance, but the knee is weaker after surgery. With mechanical assistance we may be able to strengthen and improve that joint.”


Mardula, K.L., Balasubramanian, R. & Allan, C.H. (2014) Implanted passive engineering mechanism improves hand function after tendon transfer surgery. Hand. DOI: 10.1007/s11552-014-9676-0