PNS Motor Stimulation Study

Paralysis is one of the most disabling features of Spinal cord injury and stroke. In select cases, where the nerve is intact, stimulation can achieve meaningful muscle contraction e.g. to restore grip and release function. Previously, products to serve this purpose had been developed and successfully implanted (Freehand device). However, they had technical and cost limitations and have gone out of production. This concept of functional electrical stimulation has also been utilised with external orthoses, however the applicability has been limited both due to the precision required in applying the external device each time and the need of someone else to put this on, defeating the purpose.

We aim to investigate if a simple implantable and commercially available system could replicate the same function. Curonix (formerly StimWave) wireless PNS is one such system that is already CE marked and FDA approved for stimulation of peripheral nerves. It is currently used for stimulation of peripheral nerves for pain relief.

During programming for the same, to check for adequate placement, motor stimulation is routinely performed which elicits corresponding muscle twitch. Even though the parameters are approved for safety, it has not been used to generate a clinically meaningful sustained muscle contraction.

Patients implanted with a wireless peripheral nerve stimulation (PNS) system for chronic pain in the upper limb shall be identified and approached for consent. Surface electromyography (EMG, baseline and with active contraction) shall be performed to confirm intact motor nerves. Baseline MRC (Medical Research Council Scale for Muscle Strength) grade shall be assessed. PNS shall be programmed to produce muscle contraction (within FDA approved safe limits for the device) with the EMG monitoring. The muscle contraction shall be recorded on video for further evaluation. Strength of contraction shall be assessed on the MRC scale. Stimulation parameters shall be then re-adjusted to pain-relief setting. Neurological examination shall be performed and return to baseline EMG ascertained.

Data shall be analysed and the Study shall end when the data for the last participant shall be gathered.

If proven to be successful, the Curonix wireless PNS system has the potential capability for generating voice controlled coordinated contraction of 2-3 electrodes, all of which can be placed under local anaesthetic as day case. A system has also been developed in parallel to provide sensory feedback which will automatically adjust the strength of contraction so that the grip is adequate.

Inclusion criteria

• Male or Female, aged 18 years or above with implanted Curonix (formerly: Stimwave) PNS for radial, ulnar or median nerve;
• Functioning lower motor neuron (LMN) pathway determined by baseline EMG.

Exclusion criteria

• Age <18yr;
• Myopathy and other LMN disorders;
• Impaired LMN pathway determined by EMG.