Upper limb amputation causes a devastating disability. In the United States, an estimated 41,000 people live with arm amputation at or above the wrist (Ziegler-Graham et al. 2008); worldwide, this number is in the millions. The majority of unilateral and bilateral arm amputations are caused by trauma, such as industrial accidents, motor vehicle collisions, and-quite poignantly in this day and age-battlefield injuries. The next most common cause of arm amputation is dysvascular disease (Dillingham et al. 2002). Arm amputation can also be necessary in order to remove cancer, although improvements in cancer treatments and limb-sparing surgical techniques have made this less common. Finally, congenital limb deficiency, which occurs in 0.02% to 0.07% of live births (Ephraim et al. 2003), affects the upper limb in more than 50% of cases (Dillingham et al. 2002). Since trauma is the primary mechanism of upper limb amputation, the average age at which amputation occurs is quite young. Thus these individuals must live for decades with the consequences of losing a limb.