Targeted Muscle Reinnervation for the Upper and Lower Extremity

Abstract

Myoelectric devices are controlled by electromyographic signals generated by contraction of residual muscles, which thus serve as biological amplifiers of neural control signals. Although nerves severed by amputation continue to carry motor control information intended for the missing limb, loss of muscle effectors due to amputation prevents access to this important control information. Targeted Muscle Reinnervation (TMR) was developed as a novel strategy to improve control of myoelectric upper limb prostheses. Severed motor nerves are surgically transferred to the motor points of denervated target muscles, which, after reinnervation, contract in response to neural control signals for the missing limb. TMR creates additional control sites, eliminating the need to switch the prosthesis between different control modes. In addition, contraction of target muscles, and operation of the prosthesis, occurs in reponse to attempts to move the missing limb, making control easier and more intuitive. TMR has been performed extensively in individuals with high-level upper limb amputations and has been shown to improve functional prosthesis control. The benefits of TMR are being studied in individuals with transradial amputations and lower limb amputations. TMR is also being investigated in an ongoing clinical trial as a method to prevent or treat painful amputation neuromas.

Figure 1

Coaptation of large donor nerve (blue arrow) to small motor point (green arrow)

Figure 2

Diagram of residual limb (ventral view) after transhumeral amputation showing muscles innervated by transferred nerves (blue) and intact native nerves (green) and, in parentheses, prosthetic function controlled by each muscle

Figure 3

Dissection showing adipofascial flap and segments of pectoralis major in individual with shoulder disarticulation amputation.

Figure 4

Typical nerve transfers in shoulder disarticulation patient.

Figure 5

Median nerve transfer to motor branch (Br) of FDS for transradial TMR.