We've seen a number of robotic prosthetic hands intended for amputees, but what about those that still have their hands but have lost function through nerve damage? Researchers at Oregon State University (OSU) have tackled the problem and come up with an implant consisting of a simple pulley system that would more effectively transfer mechanical forces and allow more natural grasping function with less effort.

Unlike the nerve transfer technique we looked at a couple of years ago that reroutes nerves in the upper arms of patients with spinal cord injury at the C7 vertebra to restore some hand function, the technique developed at OSU connects multiple finger tendons to a single muscle via a passive hierarchical artificial pulley system.

This differs from surgical approaches currently used to restore gripping capabilities in hands following nerve damage that involve directly attaching finger tendons to a still-functioning muscle. The downside of such tendon-transfer surgery is that hand function remains significantly impaired, with large amounts of force needing to be exerted and all fingers moving at the same time, rather than separately.

The OSU team has tested their pulley system, which has no sensory, electronic or motor capabilities, in cadaver hands. They found that the passive system can produce more natural and adaptive flexion of the fingers in grasping, with the amount of force needed to close all four fingers around an object reduced by 45 percent and slippage when grasping an object reduced by 52 percent.

"This technology is definitely going to work, and it will merge artificial mechanisms with biological hand function," said Ravi Balasubramanian, an assistant professor in the OSU College of Engineering.

Although they have only tested the system in hands, the researchers say it has the potential to improve function in a wide range of damaged joints.

"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."

But Balasubramanian goes further, suggesting such mechanized assistance systems could be used to develop joints or limbs that mechanically function better than they did before an injury.

"There’s a lot we may be able to do," he said. "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."

The team from OSU and the University of Washington's School of Medicine reported their findings in the journal Hand.