Brachial plexus injuries can cause severe disabilities and often affect young adults and newborn children. When initial conservative treatment or nerve surgery fails, muscle/tendon transfers are the only current treatment options available to regain a functional arm. During this extensive surgery a healthy donor muscle is transposed to exert a different function. After long-term denervation the muscle is irreversibly changed. Muscle atrophy, fattening, fibrosis, decrease in capillary to muscle fiber ratio and decline in the number of satellite cells, which are responsible for post-natal muscle repair, is seen. For neuromuscular diseases, cell therapy aiming at rescuing muscle damage by delivery of cells that can differentiate into skeletal muscle, might be a promising approach. Safety questions remain whether stem cell injection results in non-muscle tissue formation like inflammatory cells or connective tissue formation in the transplanted muscles. Furthermore, it remains to be determined whether these stem cells undergo functional integration and enhance muscle function. The objective of this pilot study is to assess functional and morphological improvement of the m. biceps brachii after autologous bone marrow-derived mononuclear cell injection.