Long-term effects of finger amputation on stump skin sensibility and digital nerve conduction

Stability and selectivity of a chronic, multi-contact cuff electrode for sensory stimulation in human amputees

OBJECTIVE

Stability and selectivity are important when restoring long-term, functional sensory feedback in individuals with limb-loss. Our objective is to demonstrate a chronic, clinical neural stimulation system for providing selective sensory response in two upper-limb amputees.

APPROACH

Multi-contact cuff electrodes were implanted in the median, ulnar, and radial nerves of the upper-limb.

MAIN RESULTS

Nerve stimulation produced a selective sensory response on 19 of 20 contacts and 16 of 16 contacts in subjects 1 and 2, respectively. Stimulation elicited multiple, distinct percept areas on the phantom and residual limb. Consistent threshold, impedance, and percept areas have demonstrated that the neural interface is stable for the duration of this on-going, chronic study.

SIGNIFICANCE

We have achieved selective nerve response from multi-contact cuff electrodes by demonstrating characteristic percept areas and thresholds for each contact. Selective sensory response remains consistent in two upper-limb amputees for 1 and 2 years, the longest multi-contact sensory feedback system to date. Our approach demonstrates selectivity and stability can be achieved through an extraneural interface, which can provide sensory feedback to amputees.

Phantom finger phenomena and the effects of toe-to-finger transplantation

Phantom finger phenomena and the effects of toe-to-finger transplantation were studied in 76 patients who had had traumatic finger amputation. Phantom finger phenomena were observed in 48 (63%) patients with the presence of phantom finger only in 30, phantom finger with sensation in nine, and phantom finger with motion also in nine. After toe transplantation, phantom finger phenomena disappeared immediately in about half of the transplanted fingers that had phantom phenomena before toe transplantation, and also in about half of the amputated fingers without the surgery. Conversely, phantom toe phenomena occurred in 13 (17%) patients. Although some patients had mild-to-moderate unpleasant phantom sensations, none had severe or distressing phantom finger pain or phantom toe pain. It is concluded that phantom phenomena occurred in both finger and toe amputations, and that toe-to-finger transplantation appeared to facilitate the disappearance of phantom phenomena not only in the transplanted fingers but also in the amputated but untransplanted fingers. Possible mechanisms for these observations are discussed.