A Pilot Trial to Assess Implantable Myoelectric Sensors (IMES) to Improve Prosthetic Function for Transhumeral Amputees with Targeted Muscle Reinnervation

Estimates place the prevalence of major upper limb amputation in the United States at 41,000 individuals, more than 80% of which have been the result of a trauma-related injury, including combat. While the past decade has yielded modest gains in prosthetic devices, abandonment rates remain high. The results of one recent survey looking at satisfaction and prosthetic-device use in Service members who suffered combat-related unilateral upper-limb amputation showed that 30% of Soldiers from Vietnam and 22% of Soldiers from Operation Iraqi Freedom/Operation Enduring Freedom (OIF/OEF) abandoned prosthesis use altogether, complaining of weight, discomfort, pain, lack of functionality, and poor fit. This rate was significantly higher for those with transhumeral and more proximal amputations, among whom prosthetic abandonment was found to be 40% (Vietnam) and 42% (OIF/OEF). Even the most advanced myoelectric upper limb prosthetics have high rejection rates; 23% by some accounts. The limited dexterity of control with these devices has often been cited as the primary reason for their abandonment. While the negative functional implications of abandoning of an upper limb prosthesis are obvious, individuals who rely on only one arm/hand for daily use are also at a much higher risk of developing overuse injuries and arthritis of their neck, upper back, and remaining limbs, further negatively influencing long-term morbidity and quality of life.

Current motorized upper limb prosthetics (myoelectric prosthetics) are controlled by surface electrodes that are placed on the skin of the individual's amputated limb. These electrodes record electrical activity generated by the contraction of muscles that remain within the residual limb. A significant limitation of using surface electrodes is their frequent loss of reliable signaling, especially during times when the residual limb begins to sweat or when the electrodes shift in location as the socket often moves during activities of heavy lifting or when manipulating objects while reaching overhead or below the waist. Other limitations include their ability to only pick up muscles close to the surface of the skin, rather than deeper muscles that allow more natural control. Furthermore, conventional surface sensing systems do not allow control of multiple degrees of freedom at one time (i.e., elbow, wrist, and hand motion). Therefore, one must first control the elbow, then the wrist, and then the hand in stepwise and sequential fashion rather than being able to manipulate all of these functions in a coordinated and intuitive manner to control the prosthesis in three-dimensional space. These issues make control inconsistent and unreliable, which can frustrate users.

This proposal aims to determine the feasibility of utilizing implantable myoelectric sensors (IMES) to control a transhumeral myoelectric prosthesis in patients who have already undergone targeted muscle reinnervation (TMR) in order to provide advanced user intent control of an upper-limb prosthesis. In over 75 patients to date, TMR has demonstrated that the remaining transected peripheral nerves in the residual limb can be successfully re-connected to residual limb muscles to create additional myoelectrical sites of control for a prosthesis. Despite its promise for restoring intuitive control to amputees, current TMR systems continue to be limited by control strategies that utilize surface recording electrodes. We believe that combining TMR with a better interface and control strategy will result in greater user performance, intuitive control, and increased functionality. IMES are self-contained electrodes that are inserted into residual limb muscles and are able to record and transmit muscle electrical activity wirelessly to control a prosthetic hand. In the first Food and Drug Administration-approved human feasibility study, currently being carried out by researchers at Walter Reed National Military Medical Center in collaboration with the Alfred Mann Foundation, preliminary results in the first human subject demonstrate that IMES can be used safely and effectively to control a transradial prosthesis with improved accuracy and function as compared to using surface electrodes.

The overall objective of this grant is to improve functional independence for individuals with transhumeral amputation by demonstrating successful simultaneous control of a three degree of freedom prosthetic arm, utilizing implantable myoelectric sensors IMES in individuals who have successfully undergone previous TMR surgery. The strength of this research proposal is twofold: (1) TMR surgery is a well-established, viable method for restoring intuitive control of a prosthetic devices for transhumeral amputees and (2) prior experience from our research team has demonstrated the successful implantation of the IMES system in a transradial amputee, which has provided superior function as compared to the existing problems with usi .......