Improved myoelectric prosthesis control accomplished using multiple nerve transfers.
BACKGROUND
The control of shoulder-level disarticulation prostheses is significantly more difficult than that of prostheses for more distal amputations. Amputees have significant difficulties coordinating the separate functions of prosthetic shoulder, elbow, wrist, and hand/hook components. The user must lock one joint at a particular position in space before subsequently moving a different joint.


METHODS
A patient with bilateral humeral disarticulations after an electrical injury underwent a novel nerve transfer procedure designed to improve the control of a myoelectric prosthesis. The median, radial, ulnar, and musculocutaneous nerves were transferred to the nerves of segments of the pectoralis major and minor muscles. Those muscles then act as bioamplifiers of peripheral nerve signals when the normal upper extremity nerves are activated by the patient's brain. Therefore, when the patient thinks "flex elbow," the transferred musculocutaneous nerve fires, and a segment of the pectoralis major contracts. An electromyographic signal is then detected transcutaneously and causes the prosthetic elbow to flex.


RESULTS
Three of the four nerve transfers were successful. One of the nerve transfers unexpectedly yielded two separate controllable muscle segments. Standardized testing using a "box-and-blocks" apparatus was performed with the patient's previous myoelectric device and the current device after nerve transfers. The patient's performance improved by 246 percent.


CONCLUSIONS
Nerve transfers to small muscle segments are capable of creating a novel neural interface for improved control of a myoelectric prosthesis. This is done using standard techniques of nerve and flap surgery, and without any implantable devices.
Hijjawi
John B
JB
Chicago, Ill. From the Department of Surgery, Division of Plastic Surgery, and Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, and the Neural Engineering Center for Artificial Limbs, Rehabilitation Institute of Chicago.
Kuiken
Todd A
TA
Lipschutz
Robert D
RD
Miller
Laura A
LA
Stubblefield
Kathy A
KA
Dumanian
Gregory A
GA
D001132:Arm; D001186:Artificial Limbs; D004594:Electrophysiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology / Q000601:surgery; D016067:Nerve Transfer / Q000379:methods*; D011474:Prosthesis Design