Abstract—We have developed a multi-channel electrogmyography sensor system capable of receiving and processing signals from up to thirty-two Implanted MyoElectric Sensors (IMES). The appeal of implanted sensors for myoelectric control is that EMG signals can be measured at their source providing relatively cross-talk free signals that can be treated as independent control sites. An external telemetry controller receives telemetry sent over a transcutaneous magnetic link by the implanted electrodes. The same link provides power and commands to the implanted electrodes. Wireless telemetry of EMG signals from sensors implanted in the residual musculature eliminates the problems associated with percutaneous wires such as infection, breakage and marsupialization. Implants are designed for permanent long-term implantation with no servicing requirements. We have a fully operational system. The system has been tested in animals. Implants have been chronically implanted in the legs of 3 cats and are still completely operational 12 months after implantation. The recordings are stable and reliable over the chronic recording period.

I. INTRODUCTION ERSONS with recent hand amputations expect modern hand prostheses to function like intact hands.

Unfortunately, current state-of-the-art electric prosthetic hands are generally single degree-of-freedom (opening and closing) devices that function and are controlled very differently than the natural hand. Prosthetic arms that allow multi-degree-of-freedom (DOF) movements require sequential control of these multiple motions, using locking mechanisms and/or special switch signals to change control from one degree-of-freedom to the next, which is slow and counter intuitive, and results in the device being under-utilized or rejected [1] Consideration of both current and experimental control approaches drove the system requirements for our Implantable Myoelectric Sensor (IMES) system. The major factor limiting the development of more sophisticated hand/arm prostheses is not hand/arm mechanisms themselves but rather the difficulty in finding sufficient control sources to control the many DOFs required to replace a physiological hand and/or arm. Development of an Implantable MyoElectric Sensor (IMES) system that uses information from implanted sensors telemetered over a transcutaneous (no wires) magnetic link allows multiple control sources to be created by recording myoelectric signals at their source from each of the residual muscles in

Manuscript received 16 July, 2008. This work was supported in part by the NIH under Grant 1 R01 EB01672-01.

J. F. Schorsch is with the Rehabilitation Institute of Chicago, Chicago, IL, 60611 (phone: 312-238-1570 email: j-schorsch@northwestern.edu)

R. F. ff. Weir is with the Rehabilitation Institute of Chicago, Chicago, IL, 6061

the amputated limb. The IMES system can be viewed as a platform technology

for making long-term intramuscular recordings. We have demonstrated the functionality and reliability of the system on the bench and we have fully operational systems that have been tested both acutely and chronically in animals. Benchtop reliability has been assessed by comparision to commercially available EMG acquisition systems (Noraxon TeleMyo 2400, Noraxon AZ). Chronic reliability is being evaluated by examination of statistical markers found in the frequency spectrum [2]. Implants have been chronically implanted in the legs of 3 cats and all implants are completely operational 1 year post-implantation.

ACKNOWLEDGMENT R. F. ff. Weir and J. F. Schorsch would like to thank Dr.

C. J. Heckman, Michael Johnson, and Jack Miller for their expertise and assistance as well as the staff of the Northwestern Center for Comparative Medicine for their advice and assistance.

REFERENCES

[1] D. Atkins, D. C. Y. Heard, and W. H. Donovan, “Epidemiologic overview of individuals with upper-limb loss and their reported research priorities,” Journal of Prosthetics and Orthotics, vol. 8, no. 1, pp. 2-11, 1996.

[2] M. Bilodeau, A. B. Arsenault, D. Gravel et al., “EMG power spectrum of elbow extensors: a reliability study,” Electromyogr Clin Neurophysiol, vol. 34, no. 3, pp. 149-58, Apr-May, 1994.

Jack F. Schorsch and Richard F. ff. Weir, Member IEEE

Reliability of Implantable MyoElectric Sensors (IMES)

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Fig.1. Normalized power spectrum densities from chronic cat #70609. Data from lateral gastrocnemius during self selected walking. Filtered with 3rd order butterworth bandpass filter with 25hz-1000hz corner frequencies to remove low-band 3hz gait information. Power spectrum calculated via non-overlapped 512 point Blackman window over length of walking event (50kSamples).

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