Reducing pain in phantom limbs
Michael J. Lander
Many individuals who have undergone amputation of an arm or leg experience pain in the missing limb — a phenomenon referred to as phantom limb pain. The sensations can seem as real as aches and pains in the rest of their body. To help people deal with this condition, the mirror box was developed more than 10 years ago. The device enables users to interpret motion of their functioning limb as movement of their phantom one, but only within the mirror’s limited field of view.
Craig D. Murray, Stephen Pettifer and colleagues at the University of Manchester and at South Manchester University Hospitals, both in the UK, have assembled a system that operates on the same concept but that re-creates motion of the phantom limb through virtual reality. As a result, the setup permits users to perform a wider range of activities than with the mirror box.
Screen shots from a virtual reality device show activities completed by individuals with phantom limb pain. In one exercise, participants attempt to push away a ball that is moving toward them in space. Once they complete this task successfully, the ball disappears into a wall and another one replaces it.
The researchers combined a virtual reality head-mounted display from Virtual Research Systems Inc. with sensors and a data glove from 5th Dimension Technologies for attachment to the functional limb. A Polhemus motion tracking device measured movements of the head, arms and legs. Together, the components gave participants the illusion that they were in a room and that they possessed an intact arm or leg in place of their phantom limb.
Over a course of 10 weeks, participants completed seven to 10 sessions with the system. Three individuals had undergone an arm amputation and two had suffered from phantom pain in the leg. During each 30-minute period, they completed four tasks, including placing their phantom limb on colored tiles that lit up in a particular sequence, hitting or kicking a virtual ball, tracking the motion of a moving virtual stimulus and directing a stimulus toward a target.
In another activity, users place their foot on illuminated squares that light up in sequence (top). Participants also can attempt to kick a slowly moving ball (middle). An additional task includes moving a ball toward a target, in this case, a lit circle. All of the tasks are designed to encourage phantom limb movement (bottom).
The researchers collected qualitative data through interviews after each session. Throughout the investigation, the participants also kept a journal in which they described their experience. After each session, as well as after completion of the study, they completed additional questionnaires and tests to assess therapeutic effects and pain levels.
Analysis of the data seemed to indicate that the therapy brought temporary relief to individuals who had recently undergone amputation, especially to those with phantom arms or legs that felt paralyzed. For some participants, however, reports were contradictory. In all cases, the long-term effectiveness of the technique remains unknown.
Currently, to obtain more statistical evidence, the researchers are setting up trials that include more participants. They believe that future studies must incorporate a variety of training regimens as well as an investigation of any placebo effects of the system caused by the novelty of the tasks. Such analyses could help researchers understand which individuals would benefit most from the therapy.
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