Myoelectric Signal Transmission from Implanted Epimysial Electrodes Using a Bone-Anchor as a Conduit

Introduction Current Upper-limb myoelectric prostheses rely on only 2 control signals from surface electrodes, placed over antagonistic muscles in the amputation stump, for limb control. While this has benefits over the traditional body-powered control, there are disadvantages; electrode lift-off, impedance variation, cross-talk, reliability, and limitations in intuitive control. To address these problems, electrodes can be implanted directly on individual muscles responsible for specific actions. Not only does this address skin-related issues, it reduces cross-talk and greatly increases the number of control channels for multi degrees of freedom intuitive control. Bone-anchored devices can be used to overcome problems with prosthetic attachment and additionally used to transfer control signals from these implantable electrodes to the prosthesis. [1] In above-elbow amputees, targeted muscle reinnervation (TMR) enables more signal generation by redirecting nerves previously controlling the amputated muscles in the forearm, to surrogate muscles in the torso (e.g. pectoralis major). [2] We describe in vivo model using implantable electrodes to record myoelectric signals (MES) in normal muscles and following TMR, utilizing a bone-anchor as a conduit to carry signals across the skin barrier. Materials and Methods An in vivo n=6 ovine model was used. A bone-anchor was placed trans-tibially and bipolar electrodes sutured to M. Peroneus Tertius (PT). In a further n=1, motor nerve to PT was divided and coapted with a motor branch from peroneal nerve. MES were recorded over a 12-week period. Functional recovery in the TMR model was assessed by MES and force-plate analysis (FPA). Results In the n=6 group, there was a positive correlation between signal to noise ratio (SNR) and time since implantation (p < 0.005), with a mean SNR of 7 by week 12. In the TMR model, functional recovery was observed after 6 weeks. Difference between legs returned to normal (pre-op: left 4.7 N/kg, right 4.8 N/kg; 80 days post-op: left 4.1 N/kg, right 4.3 N/kg). Recorded MES from TMR muscle compared favourably with healthy muscle. Conclusions We have demonstrated that a bone-anchor is a reliable and robust conduit for transmitting MES over a period of 12 weeks. The combination of implanted electrodes & direct skeletal fixation offers clear advantages over current systems for prosthetic attachment & control. This system forms the basis of a complete solution for prosthetic rehabilitation, which can also be used in the context of TMR. References 1. Al Ajam et. al., 2013. PMID: 23358938 2. Kuiken et. al., 2004. PMID: 15658637