Cortical excitability of the biceps muscle after intercostal-to-musculocutaneous nerve transfer.

OBJECTIVE: Restoration of volitional control over elbow flexion has been demonstrated in patients who have undergone intercostal-to-musculocutaneous nerve transfer. We investigated the cortical area involved in the control over elbow flexion after intercostal-to-musculocutaneous nerve transfer.
METHODS: Maps of magnetically excitable cortical areas of the affected arms of five patients were compared with maps of their healthy arms and maps of both arms of four healthy control subjects. The intercostal cortical area was also studied, requiring needle electromyography mapping (n = 1).
RESULTS: The cortical areas of affected arms were smaller and less excitable than those of healthy arms. The locations of these areas could not be distinguished from that of the normal cortical biceps area but seemed to differ from that of the intercostal cortical area.
CONCLUSION: The existence of a biceps-like cortical area related to the reinnervated muscle can be explained in two ways. Interneurons from the original biceps area might excite the cortical neurons controlling the intercostal muscles. Alternatively, corticospinal neurons of the original biceps area may project directly onto spinal intercostal motor neurons. Cerebral plasticity does occur in intercostal-to-musculocutaneous nerve transfers and may be crucial for their clinical success.