Journal of Rehabilitation Medicine 51-3 | Page 63
J Rehabil Med 2019; 51: 209–216
ORIGINAL REPORT
TOUCH ON PREDEFINED AREAS ON THE FOREARM CAN BE ASSOCIATED WITH
SPECIFIC FINGERS: TOWARDS A NEW PRINCIPLE FOR SENSORY FEEDBACK IN
HAND PROSTHESES
Ulrika WIJK, OT, MSc 1 *, Pamela SVENSSON, MSc 2 *, Christian ANTFOLK, PhD 2 , Ingela K CARLSSON, OT, PhD 1 , Anders
BJÖRKMAN, MD, PhD 1 and Birgitta ROSÉN, OT, PhD 1
From the 1 Department of Translational Medicine – Hand Surgery, Lund University and Skåne University Hospital, Malmö and 2 Department
of Biomedical Engineering, Faculty of Engineering, Lund University, Lund, Sweden
*These authors contributed equally to this article.
Objective: Currently available hand prostheses lack
sensory feedback. A “phantom hand map”, a referred
sensation, on the skin of the residual arm is a pos
sible target to provide amputees with non-invasive
somatotopically matched sensory feedback. How
ever, not all amputees experience a phantom hand
map. The aim of this study was to explore whether
touch on predefined areas on the forearm can be as
sociated with specific fingers.
Design: A longitudinal cohort study.
Subjects: A total of 31 able-bodied individuals.
Methods: A “tactile display” was developed consis
ting of 5 servo motors, which provided the user with
mechanotactile stimulus. Predefined pressure points
on the volar aspect of the forearm were stimulated
during a 2-week structured training period.
Results: Agreement between the stimulated areas
and the subjects’ ability to discriminate the stimula
tion was high, with a distinct improvement up to the
third training occasion, after which the kappa score
stabilized for the rest of the period.
Conclusion: It is possible to associate touch on in
tact skin on the forearm with specific fingers after a
structured training period, and the effect persisted
after 2 weeks. These results may be of importance
for the development of non-invasive sensory feed
back systems in hand prostheses.
Key words: artificial limbs; amputation stumps; sensory
feedback; upper extremity.
Accepted Dec 20, 2018; Epub ahead of print Feb 27, 2019
J Rehabil Med 2019; 51: 209–216
Correspondence address: Birgitta Rosén, Department of Hand Sur-
gery, Skåne University Hospital, SE-205 02 Malmö, Sweden. E-mail:
[email protected]
L
osing a hand is devastating to the individual, with
large physical and psychological consequences
(1). The loss of sensibility and motor functions is a
major problem for the affected individual. Advances
in engineering have made it possible to build more
advanced hand prostheses with improved grasping
alternatives and range of motion (2, 3), but there is no
hand prosthesis that is even close to replacing all of
the lost functions (1). Control of motor functions in the
hand is highly dependent on sensory feedback (4). One
LAY ABSTRACT
A drawback of currently available hand prostheses is the
lack of sensory feedback. Some amputees experience a
feeling of touch of the amputated hand when the resi-
dual limb is touched. This kind of referred sensation is
called “phantom hand map”. However, not all amputees
experience “phantom hand map”. Therefore, we exami-
ned whether touch on predefined areas on the forearm
can be associated with specific fingers in individuals with
an intact arm, using a tactile display during a 5-week
training period. In conclusion, it is possible to learn to
associate touch on predefined areas on the forearm with
specific fingers after a structured training period, and
the effect persisted after 2 weeks. These results may
be of importance for the development of non-invasive
sensory feedback systems in hand prostheses.
priority in prosthetic design that is desirable among
arm amputees is how to provide the user with sensory
feedback (2, 3, 5–9). It has been shown that sensory
feedback improves grasping control and performance
with myoelectric hand prostheses in inexperienced
users (10, 11). Both invasive and non-invasive sensory
feedback systems are under development (2, 9, 12–19).
Following an arm amputation, a phenomenon des-
cribed as referred sensation may occur. It is described
as an experience of touch of the phantom fingers when
touching the skin of the forearm and is herein called
a “phantom hand map” (PHM) (20, 21). The PHM is
unique for each individual and can differ from 1 or 2
diffusely located areas on the residual forearm with
referred sensations, to a very detailed map with several
specific areas where touch is experienced as touching
the lost hand (20, 21). Furthermore, when touching
specific areas in the PHM there is cortical activation
in the primary somatosensory cortex (S1), which
very closely resembles activation seen after touching
the different fingers in an able-bodied subject (22).
A non-invasive method for sensory feedback in hand
prostheses utilizing the PHM has been presented (23).
For non-invasive sensory feedback, a 3-fold process
is required; firstly, a registration of the tactile stimuli by
sensors is needed, secondly, actuators for transferring
the stimuli from the sensors to the user, and thirdly, a
process of relearning is necessary with adaptation in
This is an open access article under the CC BY-NC license. www.medicaljournals.se/jrm
Journal Compilation © 2019 Foundation of Rehabilitation Information. ISSN 1650-1977
doi: 10.2340/16501977-2518