Upper and lower motor neuron lesions in tetraplegia: implications for surgical nerve transfer to restore hand function.

Nerve transfers (neurotizations) performed under optimal conditions can restore some voluntary control in muscles of the upper extremities in patients with tetraplegia. However, the type of motoneuron lesions in target muscles for nerve transfers influences the functional outcome. Using standardized maps of motor point topography, surface electrical stimulation reliably defines the kind and extent of motoneuron lesion in the selected muscles. In a muscle with an intact lower motor motoneuron, nerve transfers can often successfully reinnervate the chosen key muscle. Conversely, in a lower motoneuron lesion, the nerve transfer outcome is less predictable. However, direct muscle stimulation appears to ameliorate the morphological precondition, a finding that necessitates new preoperative approaches to optimize reinnervation in denervated/partially denervated muscles. Therefore, understanding the impact of electrical stimulation in diagnostics, prognostics, and treatments of upper limbs in tetraplegia is critical for neurotization procedures.