For some amputees, local stimulation such as static or dynamic pressure, vibration and electrical stimulation applied to specific areas of the skin can modulate the phantom sensations. Global stimulation arising from more generalised contact with the prosthetic socket that joins the residual limb to the prosthesis can also influence these sensations.
Dr Jozina de Graaf of Aix-Marseille University in France believes that global and local stimulation can be utilised to provide somatosensory feedback and thus facilitate walking in amputees. Working with colleagues, she sought to modify the phantom sensations experienced by a lower limb amputee by manipulating the interface used for the prosthesis.
An individual aged 48 years who had undergone traumatic transfemoral amputation of his left leg 5 years ago was studied. He wore a prosthesis every day, which comprised an adherent semi-rigid socket without a sleeve, and he could already walk long distances.
In the first phase, Dr de Graaf and her colleagues obtained a detailed description of the participant’s non-painful and painful phantom sensations as well as the factors influencing them. In the second stage, they explored the areas of the participant’s residual limb where stimulations would induce or modify the phantom sensations. The participant reported experiencing phantom sensations during pressure.
Based on this, in the third phase, the researchers designed and applied a patch within the socket of the prosthesis to administer pressure on the participant’s skin areas and induce phantom sensations that could potentially be useful for walking. They did this under four different prosthetic interface conditions: a rigid and a semi-rigid socket, each one with and without a focal pressure increase on a specific area of the residual limb.
The phantom sensations reported by the participant during walking differed according to the four interface conditions, confirming the effectiveness of the overall approach. In addition, the different types of interfaces had different effects, both on the participant’s sensations of tingling in the foot, perceptions of the calf and on his gait pattern. Overall, the participant expressed a preference for the semi-rigid socket with a patch – which he even asked to keep at the end of the study.
This preliminary but important study provides strong support for considering non-painful phantom sensations experienced by lower limb amputees in the early rehabilitation stage, and in particular for adopting a personalised approach to prosthesis design, in order to maximise patient outcomes. Dr de Graaf and her colleagues are continuing this critical work in their ongoing research.
