Injury zone denervation in traumatic quadriplegia in humans

In order to obtain an electrophysiological characterization of the injury zone in traumatic quadriplegia, we performed electromyography and nerve conduction studies on the upper limbs of 15 patients with cervical cord trauma. Evidence of significant axonal loss was found in multiple myotomes of all patients. In most cases, the level of the most severe denervation, as determined by the absence or diminution of the compound motor action potential and the density of fibrillation potentials, was 2-5 spinal segments below the clinically and radiologically defined injury levels. In patients with injuries, the rostral extent of which is at C5 or higher, the most obvious clinical and electromyographic denervation was seen in the intrinsic hand muscles (C8/T1), with complete loss of C8/T1 motor axons in a subset of these patients. Our results document that spinal cord trauma can cause loss of motor axons in regions several segments caudal to the rostral level of injury. This finding may have implications for the pathophysiology of secondary injury, for recovery potential, and for the design of rehabilitation strategies.