April 7, 2017

Hearing, Touch Transmit Sensations Via Osseointegrated Prostheses

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Driving is an example of when the patients benefit from osseoperception. Photograph by Susanne Lindholm, courtesy of Chalmers.

A team of researchers from Italy and Sweden have found that people with an osseointegrated prosthesis can hear by means of vibrations in their implants. This sound transmission through bones is a part of osseoperception—a sensory awareness arising from the mechanical stimulation of an osseointegrated prosthesis—and may help people with upper- and lower-limb amputations get back tactile sensations and perceive natural sensations while grasping an object or walking on uneven terrain. By shedding new light on the tactile and auditory perception of humans, this discovery can be used to develop improved prostheses.

The investigation was a collaborative effort between researchers with Scuola Superiore Sant’Anna (SSSA), Pisa, Italy, and researchers with Chalmers University of Technology, Sahlgrenska University Hospital, and the University of Gothenburg, all in Gothenburg, Sweden. The study describing their work was published March 28 in Scientific Reports.

The transmission of sound through skull bones is a well-known phenomenon; however, it was not clear whether this also occurs through bones in the arms and legs and thus contribute to osseoperception. Until now, the consensus was that the sense of touch and the improved mechanical stability of the prosthesis were the cause of the phenomenon.

“Using four 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 doctoral student from the SSSA Biorobotics Institute. He conducted the experiments at the Chalmers Biomechatronics and Neurorehabilitation Laboratory (BNL).

The researchers carried out tests on 12 patients with different levels of upper- and lower-limb amputations. 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,” said Max Ortiz Catalan, PhD, head of the BNL and supervisor of the research. “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.”

Editor’s note: This story was adapted from materials provided by SSSA and Chalmers.

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