Rerouting for Hand Function
Life-enhancing function may result from nerve transfers after spinal-cord injury.
Periodically, this Healing Options series has discussed peripheral-nerve transfers or rerouting, a procedure that has considerable potential for restoring some function after SCI (PN April 2002, December 2005, and October 2010).
Basically with such transfers, peripheral nerves emanating from the cord above the injury site are surgically redirected and connected to paralysis-affected nerves below the injury site. This establishes a functional neuronal connection from the brain to previously dormant muscles. Because only a specific muscle or muscle group is restored, it is not a cure-all for paralysis; nevertheless, substantial life-enhancing function may accrue.
Easy to Understand
In spite of daunting neuroanatomical terminology, these procedures are conceptually easy to understand. For example, visualize a house in which the power to the back bedroom has been lost (i.e., area below the injury) due to a burned-out master cable (i.e., the spinal-cord injury).
Instead of fixing the master cable, you split the wire that controls the still-functioning living-room television. One segment keeps powering the TV, while the other is connected to the bedroom, totally circumventing the master cable’s damaged section.
Although some of the pioneering work was done in this country more than 50 years ago, unfortunately the procedures faded into obscurity here. The preponderance of clinical experience with them was gained in China, a country possessing one-eighth of the world’s SCI population, including many people injured in massive natural disasters. For example, nerve-rerouting was used after the 1976 Tangshan City earthquake that killed nearly a quarter million and injured 400,000 people.
A decade ago, I was invited to China to observe firsthand these surgical procedures and the stunning return of function that often resulted. My April 2002 PN article was one of the first to reintroduce the concepts to Western audiences and piqued the interest of several scientists, including Dr. Justin Brown, currently at the University of California–San Diego.
At the time a relatively junior neurosurgeon trained at some of the country’s leading medical schools, Brown was receptive to learning about innovative approaches for treating SCI, including those not well appreciated in the U.S. He open-mindedly sought the opinion of my Chinese colleagues, traveling to China to learn more.
With the understandings and insights he gained from these and other international collaborations, Brown started developing his own rerouting methodology. Although the benefits are still to be determined, his efforts are especially important because it helps to bring back to America a focus on a forgotten, function-restoring surgical approach that has benefited many Chinese.
As discussed in a 2011 issue of Surgical Neurology International, Brown has focused his initial efforts on creating new connections between still-functioning upper-arm nerves and paralysis-affected nerves servicing the lower arm and hand. Basically, his overall goal is to generate additional hand function for people with cervical injuries.
Although Brown has now rerouted nerves in several individuals, his article focuses on the procedures used with the first subject, a 28-year-old male with a C5-level injury sustained 13 years earlier from a football accident. Due to this injury, arm function was limited to the shoulders and biceps.
Four years after injury, the patient started using the “Freehand” functional-electrical-stimulation (FES) device, which allows the user to artificially pinch and grip through a system of embedded electrodes controlled by a movement-sensitive device placed on the opposite shoulder.
However, because the patient believed (1) the resulting hand control was limited, (2) the device was cumbersome, and (3) wires leading to electrodes caused discomfort, he chose to have the system removed and consider other options.
To reestablish voluntary control of various muscles involved in hand function, Brown had to create several new nerve connections. Although the procedures sound relatively straightforward in principle, they required considerable surgical sophistication and ability to identify nerves serving specific muscles.
The first new connection was created to restore wrist and finger flexion (i.e., bending). Specifically, segments (called fascicles) of the musculocutaneous nerve, which controlled the still-functioning biceps and related muscles, were connected to a segment of the median nerve, leading to paralyzed forearm and hand muscles. Because only a portion of the musculocutaneous nerve was redirected, function in the bicep-related muscles already served by this nerve was not sacrificed.
Illustration A shows the presurgery situation involving the musculocutaneous and median nerves and the muscles they serve. Muscles under voluntary control are colored red, while paralysis-affected muscles are highlighted in gray. Illustration B shows the location of the newly created musculocutaneous-median nerve connection and, as can be seen by the expanded red coloring, the additional key muscles that should come under volitional control as a result of the connection.
The next rerouting involved the axillary nerve, which serviced the patient’s still-functioning deltoid muscles.
Specifically, an axillary-nerve segment was connected to a segment of paralysis-affected radial nerve that leads to the triceps (see Illustration C inset) reestablishing a functional connection to this important muscle. Another axillary-nerve segment was connected to a radial-nerve segment that leads to wrist- and finger-extension muscles. The remaining axillary segments will continue to serve the deltoids.
After the rerouted nerves have the opportunity to regenerate to their new target muscles, the axillary nerve under the individual’s volitional control will provide functional connections to not one but several muscles.
Illustration C shows the axillary and radial nerves and the muscles they lead to before the intervention. As before, functional and paralysis-affected muscles are colored red and gray, respectively. Illustration D shows the newly created nerve connections between the axillary and radial nerves, as well as the additional muscles that should become functional due to these connections. As can be seen, the red highlighting of volitional muscle control has greatly expanded.
Although these illustrations are technical, the take-home message can be obtained by merely blurring your eyes and noting how much paralysis-affected gray areas have shifted into red areas of volitional control.
Preliminary results appear promising with the tentative return of new function, but it’s too early to report definitive outcomes in any of the patients because it takes time for the nerves to regenerate to the target muscles.
In theory, however, the patient, who before the procedure only had elbow-flexion and shoulder function, should recover the ability to reach, grasp, and release. It is important to note such recovery will be obtained without sacrificing existing functions, which is often the case with the more commonly used tendon-transfer procedures (a hand surgery in which a functioning tendon is shifted from its original attachment to a new one to restore the action lost due to paralysis).
Although Brown’s nerve-transfer procedures are restricted in anatomical focus, for people with quadriplegia, recovering even limited hand function can often have profound quality-of-life implications by greatly increasing personal independence. As such, his work eventually may have important implications for many Americans with SCI.
Rerouting for Hand Function
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