Modification of chronic phantom limb pain by using leg prostheses with sensory feedback

Status:

completed 06/2017

Aims:

Based on considerations concerning the cortical reorganization of the primary somatosensory cortex S1, we had several primary aims for this project:

• to develop a prosthesis with somatosensory feedback from the foot of the prosthesis;
• to prove whether a training with such a prosthesis with somatosensory feedback reduces phantom limb pain and increases the functionality of the prosthesis; and
• to prove whether a somatosensory discrimination training reduces phantom limb pain.

Additionally, we tried to investigate how the training with somatosensory feedback and the discrimination training will affect the cortical organization of S1.

Activities/Methods:

At the beginning, we developed different prototypes of prosthesis with somatosensory feedback. 17 patients with amputation of the lower leg performed a training with such a prosthesis with somatosensory feedback for two weeks. We recorded phantom limb pain and functionality of the prosthesis during the training period as well as during a two-week baseline period. A follow-up period and additional examinations of the anatomical and functional cerebral changes by MRI, fMRI, and MEG supplemented the investigations. The paradigm and the methods were identical for both, the training with a prosthesis with somatosensory feedback and the discrimination training.

Results:

Aim 1): The development of the prosthesis with somatosensory feedback was much more complex than expected. We started with the development of a prosthesis with complex somatosensory feedback in analogy to a previously developed system for patients with lower-arm amputation. It reveals that this feedback was too complex to be integrated into patients’ behavior. Therefore, we developed several prototypes of prosthesis with somatosensory feedback. It reveals that a technically challenging, but rather simple system with respect to information processing was the prototype preferred by the patients. This system was used for the following examination of aim 2.

Aim 2): The training with a prosthesis that provides somatosensory feedback at the stump during walking and standing increases the functionality with the prosthesis as well as the consumer satisfaction of patients. Patients reported on a more stable, better controlled walking, especially on bumpy and soft grounds, but also on larger walking distances. We found that the gait was more symmetrical. Additionally, we found a reduction of phantom limb pain during the training period as compared to baseline. This effect resulted primarily from lower pain at the end of the day, i.e. the time, where patients usually report on highest pain during the day. Similarly, most patients reported retrospectively on a reduction of phantom limb pain. Both results, higher functionality and less pain, point to important findings taking into account the rather frustrating results to treat phantom limb pain. We see an important advantage of our system as it can be used in every-day life by the patients (and is already constantly used by a part of patients who trained with us). In principle, the system and results can be transferred into praxis immediately. Moreover, the physiotherapist previously working in the project will try to use the system in a private praxis. Finally, investigating the cortical organization of SI, we found that knowledge of standard textbooks has to be changed concerning detailed representation of the lower limb in SI: it is rather organized dermatologically instead of being organized like a homunculus. Moreover, the mechanoreceptive representation of the foot itself remains in place. We expect further interesting results concerning somatosensory representation as part of the results are not yet analyzed.

Aim 3): We showed that somatosensory discrimination training reduces phantom limb pain. For this training, the reduction of phantom limb pain correlated with the performance of discrimination. This property allows for an independent contribution of discrimination training to the reduction of phantom limb pain compared to the relatively simple discrimination used in the prosthesis with somatosensory feedback. We conclude that somatosensory discrimination training and the training with a prosthesis with somatosensory feedback might represent two rather independent treatments, which might complement each in reducing phantom limb pain.

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