Project Description
Neopraxis Pty. Ltd. (Lane Cove, NSW, Australia) is manufacturing the first
implantable FES system to provide multiple benefits to suitable users with
paraplegia: Functional Upright Mobility, Lower Extremity Exercise, Pressure
Relief and Bladder Control. The 22
channel implant achieves these functions through epineural stimulation of
nerves in the lower limbs, lumbar region, sacrum and conus medullaris (Figure
1).
Figure 1
A body-worn controller, the Navigator, transcutaneously powers and controls the
implanted FES24-B stimulator via a magnetically held transmit coil (Figure 2).
Figure 2
Current pulses produced by the implanted stimulator are transferred to the appropriate electrodes via stretchable, insulated leads. The available stimulation parameters are 0-8mA, 25-500msec pulse width and a pulse frequency up to 500Hz per channel. Sensor packs attached externally to each thigh, shank and the trunk enable closed loop control of stimulation to the lower extremities (Figure 3).
Preliminary Results:
In January 2002, a male with T3 ASIA A paraplegia was implanted with the Praxis FES System at Shriners Hospitals for Children, Philadelphia. During stage one, the FES24-B stimulator was implanted and two channels connected bilaterally to the femoral nerves for stimulation of vastus lateralis, intermedius and medialis. In the second stage of surgery, 3 channels were connected to electrodes placed bilaterally in the sacral foramina at S2-4. Stimulation of the sacral nerve roots will assist with voiding of urine, bowel emptying and erection. It is anticipated that a channel connected to an epidural electrode (Medtronic Pisces Quad) at the conus medullaris will allow neuromodulation of bladder hyperreflexia without posterior rhizotomy. A third stage of surgery is to implant the remaining channels to psoas and the gluteal and sciatic nerves.
Clinical Trial
The purpose of the trial is to evaluate the safety and effectiveness of the Praxis FES System, initially in 10 subjects. The trial commenced January 2002, with sites in the US and Australia.
Subjects will undergo an initial assessment to determine suitability for the trial. Primary selection criteria are complete thoracic spinal injury, skeletal maturity and intact efferent nerves to muscles in the lower extremities and bladder. Post-operative treatment involves 4 weeks of muscle conditioning, followed by 8 weeks of training in FES standing, transfers and stepping. Home-based training will be included prior to discharge with the system to enable spontaneous use. Subjects will be assessed at 3, 6, 9 and 12 months post-implant (Figure 4).
Figure 4
Outcome Measures
Clinical utility of the Praxis FES
System will be determined using quantitative functional evaluations. Subject success requires achievement of
minimum significant results for both primary outcomes - Functional Upright
Mobility (Sit-stand-sit; 10 min stance; 6 meter walk; 6 min walk; and toilet
access FIM score of ³
5) and Bladder Control (< 60mls residual volume; FIM score of ³ 4 on
incontinence diary). Secondary outcomes
include the SF-36 to measure quality of life and the
Timed ‘Up and Go’ test to address home/community use. Data will also be collected during the pre- and post implantation
phases to investigate cost effectiveness of the system.
Conclusion
In the developing field of FES and implantable neuroprostheses, the need for safe and reliable multi-channel systems is being pursued. The Praxis FES system aims to provide such a system with multiple benefits to individuals with paraplegia.