December 4, 2007

by Anthony J. Brown, MD

NEW YORK (Reuters Health) – Transferring the remaining arm nerves of upper extremity amputees to residual chest muscles can allow these patients to feel touch sensation in the missing limb, which may someday lead to the ability to feel sensations in a prosthetic arm, according to a report in the November 26th Early Edition of the Proceedings of the National Academy of Sciences.

At present, the usefulness of artificial hands is limited by the inability of the patient to feel any touch sensation, note co-author Dr. Paul Marasco from the Rehabilitation Institute of Chicago and associates. The nerve rerouting technique, however, may one day change that.

In the current study, the researchers describe the outcomes of two patients treated with the nerve transfer method: a 54-year-old man with bilateral amputations at the shoulder due to electric burns and a 24-year-old woman with a left upper amputation caused by a motor vehicle collision.

The researchers note that transfer of the arm nerves to the chest muscles led to the innervation of overlying chest skin with sensory nerves from the amputated limb. When the patients were touched on the chest, they perceived that they had been touched in the missing limb.

Further testing showed that the touch thresholds on the reinnervated chest skin were near normal, suggesting that regeneration of large-fiber afferents had occurred.

Since the sensory nerves of the chest skin were not destroyed during the procedure, there was often overlap between native-chest sensation and new referred-hand sensation. Still, according to the report, the patients were able to clearly distinguish between the two simultaneously occurring sensations.

"Probably the biggest finding was that the new limb sensation and the native chest sensation appear to intermingle and have coexisted together, for an extended period, in the skin of the chest," Dr. Marasco told Reuters Health. "This finding was somewhat surprising in light of evidence that suggests that the new hand sensation might be incorporated into the sensation of the chest and eventually be perceived as chest."

"Our results illustrate a method for creating a portal to the sensory pathways of a lost limb. This work offers the possibility that an amputee may one day be able to feel with an artificial limb as though it was his own," the authors conclude.

Future research "will be involved in examining many of the physiological mechanisms of the reinnervation itself," Dr. Marasco said. "We are currently conducting studies to assess the amputee’s ability to sense differences in applied pressure, to sense their ability to resolve tactile and spatial input and to investigate their ability to sense vibratory input."

Proc Natl Acad Sci USA 2007.