Attach prostheses directly to people’s skeletons, and they can actually hear vibrations in their implants, according to Swedish and Italian researchers.

The discovery provides a better understanding of osseoperception – the way that people with osseointegrated prostheses can “feel” mechanical stimulation of the device.

“Until now, the consensus was that the sense of touch played the primary role in osseoperception for patients with artificial limbs fixated into their skeletons,” said Max Ortiz Catalan, head of the Biomechatronics and Neurorehabilitation Laboratory at the Chalmers University of Technology in Sweden and supervisor of the research.

The understanding that both touch and hearing matter could provide better insights into the development of novel artificial limbs. The researchers – from the Chalmers University of Technology, Sahlgrenska University Hospital and University of Gothenburg in Sweden and Scuola Superiore Sant’Anna in Italy – recently published their findings in Nature Scientific Reports.

“Using 4 different psychophysical tests, we have demonstrated that even subtle sensory stimuli can travel through the body and be perceived as sound. This hearing increases the individual’s sensory awareness, even in patients with osseointegrated implants in their legs,” said Francesco Clemente, a visiting PhD student at Chalmers from the Biorobotics Institute of Scuola Superiore Sant’Anna.

Catalan added in a Chalmers news release: “In practice, the stimuli received by the patients are perceived more strongly and carry more information because they are composed of two modalities; touch and hearing. This is an important step forward in understanding the osseoperception phenomenon and, more generally, the tactile and auditory perception of humans. This discovery may offer a new starting point for implementing novel prostheses that provide enriched sensory feedback to the user.”These results show that osseointegration, which allows for stable mechanical attachment of robotic prostheses directly to the skeleton through a titanium implant, improves patients’ functionality, comfort, and ability to perceive the world around them.

The researchers tested twelve patients with various degrees of amputation, both upper and lower limb amputees. All tests indicated that patients could perceive mechanical vibrations applied to their titanium implants, through hearing as well as touch. In particular, and synchronously with the vibrations in their arms or legs, patients reported audible sound. During the experiments, the researchers found that subjects with osseointegrated prostheses could perceive very small stimuli and react more quickly to them due to additional perception by hearing.

“In practice, the stimuli received by the patients are perceived more strongly and carry more information because they are composed of two modalities; touch and hearing,” says Max Ortiz Catalan. “This is an important step forward in understanding the osseoperception phenomenon and, more generally, the tactile and auditory perception of humans. This discovery may offer a new starting point for implementing novel prostheses that provide enriched sensory feedback to the user.”

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