Leg Prosthesis With Somatosensory Feedback Reduces Phantom Limb Pain and Increases Functionality

Abstract

Phantom limb pain (PLP) develops in most patients with lower limb amputation. Changes in the peripheral and central nervous system (CNS) are hypothesized to contribute to PLP. Based on ideas to modify neural reorganization within the CNS, the aim of the study was to test, whether prostheses with somatosensory feedback might help to reduce PLP, and increase the functionality of movement with a prosthesis. We therefore equipped the prostheses of 14 lower leg amputees with a simple to use feedback system that provides electrocutaneous feedback to patients' thigh whenever the foot and toes of the prosthesis touch the ground. Two weeks of training with such a feedback prosthesis reduced PLP, increased the functional use of the prosthesis, and increased patients' satisfaction with prosthesis use. We found a significant overall reduction of PLP during the course of the training period. Most patients reported lower PLP intensities at the end of the day while before training they have usually experienced maximal PLP intensities. Furthermore, patients also reported larger walking distances and more stable walking and better posture control while walking on and across a bumpy or soft ground. After training, the majority of participants (9/14) preferred such a feedback system over no feedback. This study extends former observations of a similar training procedure with arm amputees who used a similar feedback training to improve the functionality of an arm prosthesis in manipulating and grasping objects.

Keywords: functionality; lower leg amputation; phantom limb pain; prosthesis; prosthesis training; somatosensory feedback.

Figures

Figure 1

Experimental design. Base—baseline assessment; Pre—assessment directly before first training session; and Post—assessment after last training session. Waiting period—patients used their own cosmetic prosthesis without feedback during everyday life. Training period—patients used their own prosthesis that was equipped with a somatosensory feedback system during 10 days of prosthesis training. Prosthesis functionality was assessed using questionnaires and walking tests, PLP—phantom limb pain characteristics, CPLP—retrospective change of PLP during past 2 weeks.

Figure 2

Scheme of the technical system. (a) Sensors at the prosthesis foot detect ground contact and send signal to lower leg module (LLM) (b); LLM (b) sends information to upper leg module (ULM) (c) via Bluetooth connection; ULM (c) generates electrocutaneous stimulation signals that are applied via stimulation electrodes (d) at the thigh; inset (a) bottom view of the prosthesis foot with three sensors.

Figure 3

Scheme showing relation between gait cycle phase, switch closure, and feedback. S1—switch at heel, S2—switch at middle foot, S3—switch at bunion, E1—upper electrode signaling closure of the switch at the middle foot, and E2—lower electrode signaling closure of the switch at bunion.

Figure 4

Adjusted mean values (±SE) of ratings of current phantom limb pain in numerical rating scale in pain diary (0 = no pain, 10 = strongest pain) separated for waiting and training period—mo, morning; mi, midday; and eve, evening. Asterisk indicates significant differences in post hoc tests.