Is the F wave elicited in a select group of motoneurons?

The F wave represents only a small percentage of the motoneuron pool invaded antidromically by any single impulse. We studied 22 median nerves from 11 healthy subjects to determine whether the recurrent discharges are preferentially generated in a select group of motoneurons with certain physiologic characteristics. Partial excitation of the nerve elicited the F wave with no consistent bias toward either the lower or higher threshold motor fibers. When the fast conducting axons were progressively blocked using a collision technique, the F wave continued to appear in the remaining slow conducting axons which escaped the collision. We conclude that the recurrent discharges occur in approximately 1% of antidromically activated motoneurons irrespective of their peripheral excitability or conduction characteristics.

Muscle spindle contributions to the stretch-evoked electromyogram: nerve block studies

Application of external torque to cause joint rotation evokes electromyogram (EMG) activity in the stretched muscles. These responses were studied in the tibialis anterior (TA) and flexor carpi ulnaris (FCU) muscles of normal human subjects in conjunction with a nerve block procedure by a local anesthetic agent. In both muscles, differences were observed between the myotatic and postmyotatic portions of the evoked EMG response. During recovery from a complete nerve block, the late components of the EMG (postmyotatic and stabilizing responses) recovered to the preblock magnitude faster than the early components (myotatic and late myotatic responses). Following partial nerve block, the late EMG components were diminished to a lesser extent and recovered faster than the early EMG components. This study suggests that peripheral afferent inputs are obligatory for the myotatic and late myotatic EMG responses. The effects of peripheral afferent inputs on postmyotatic responses are to modulate these later responses. However, the absence of peripheral afferent inputs will not prevent or even delay postmyotatic responses.

Neuropathy after bupivacaine (Marcaine) wrist and metacarpal nerve blocks

A series of 49 wrist and metacarpal blocks were done with the use of 0.25% or 0.5% bupivacaine in 44 patients for surgical and therapeutic purposes. Seven patients developed hypesthesia in the blocked nerve distribution lasting from 1 week to 4 months. One patient had pain and a positive Tinel sign in a dorsal branch of a digital nerve lasting 2 1/2 months. Since no neuropathies were reported in large series of nerve blocks with bupivacaine in other anatomic areas, it is postulated that bupivacaine in anatomically confined areas can cause a transient neuropathy possibly caused by a large local dose of the drug.

Electrical stimulation at the wrist as an aid for the profoundly deaf

The development and evaluation of a sensory electrical substitution aid for the profoundly deaf is described. The aid is a small wrist-worn device which converts sound into an electrical stimulus at the wrist. The initial aim was to give profoundly deaf people useful information from ambient sounds. Evaluation of the Mark 1 aid on 15 hearing and five profoundly deaf people indicated that such a device might be of use to some deaf people. Investigation of the sensitivity of the peripheral nervous system to electrical pulse stimulation showed that information could be transmitted in a more efficient manner so a Mark 2 aid was developed which incorporated circuitry to transmit pitch information, potentially useful in lipreading. The Mark 2 aid was shown to give improved results over the Mark 1 aid in transmitting voice intonation, but gave no help in an isolated word lipreading test. A portable Mark 2 aid was developed to enable clinical trials to be carried out on profoundly deaf people.

Peripheral projections of nerve fibres in the human median nerve

Elementary sensations of definable quality were evoked by intraneural electrical stimulation of sensory units through tungsten microelectrodes inserted in the median nerve of awake human subjects. The most commonly reported sensations were tapping, pressure, dull pain and sharp pain, which correlated with recording from RA units, SA I units, C nociceptors and A delta nociceptors, respectively. All sensations were projected more often to the fingertips than to the palm. The multifocal projections of sensations recruited by excitation of small groups of neighbouring nerve fibres were significantly more scattered in space than anticipated if these fibres had preserved an orderly intraneural map, implying lack of somatotopy in the nerve. Mean projected field sizes were 3.4 mm2 for sharp pain, 9.2 mm2 for tapping/vibration, 29.3 mm2 for pressure and 35.4 mm2 for dull pain, and in addition the latter two showed a rising size gradient from fingertip to palm. Consideration of projected field size as a variable in discriminative touch suggests that input from RA units and A delta nociceptors may be of importance in stimulus localization, while SA I units may play an additional role in two point discrimination.

Somatosensory evoked potentials from musculocutaneous nerve in the diagnosis of brachial plexus injuries

A technique for recording somatosensory evoked potentials using stimulation of musculocutaneous sensory nerve fibers proximal to the wrist has been used in 10 normal subjects and in 8 patients with traumatic lesions of proximal parts of the brachial plexus. The technique gave satisfactory evoked potentials in all normal subjects and provided useful information in patients with avulsion of the 5th and 6th cervical roots. The results were similar to those obtained by radial nerve stimulation. The results in 3 patients with upper trunk injuries and in 1 patient with avulsion of the 5th cervical root were unhelpful. In 2 patients with multiple cervical root avulsions the evoked potentials from cervical cord and contralateral scalp were absent and were attenuated at Erb's point. This is the first report where musculocutaneous nerve evoked potentials have been applied to a group of patients.

Anatomic localization of sympathetic nerves in the hand

The microscopic anatomical localization of the sympathetic nerves within the peripheral nerves and their relationship to the end arteries in the hand has not been fully evaluated. A preliminary study is presented that outlines a method of microscopic identification of sympathetic nerves in the hand. Fresh human tissue consisting of median and ulnar nerves and their arterial supply were used in the study. Sections of these were taken at multiple levels in the forearm, wrist, and hand after the tissue was frozen. The sections were then immersed in a glyoxylic acid solution in order to excite catecholamine fluorescence. Dark-field fluorescence microscopy was then used to view the sections. Light microscopy was also used to examine adjacent sections from the same specimens. The sympathetics are more plentiful in the median nerve as compared to the ulnar nerve at the wrist. They are mostly located, in clusters, in the peripheral aspect of the nerve. Control material consisting of motor nerve, sympathetic chain, and adrenal gland was used to standardize the fluorescence. Histofluorescence was then used as a method to define the anatomy of the sympathetic nerves in the hand.

[Neuralgia of the dorsal interosseous nerve]

The Author refer about a pain syndrome of the wrist, characterized by nerve interosseous radial compression at carpal. A surgical enervation gives in all patients treated, a total remissione of pain.

Carpal tunnel syndrome: use of palmar stimulation of sensory fibers

In early or mild carpal tunnel syndrome (CTS), where the segment of median nerve sensory fibers is neurapraxic, stimulation of the nerve distal to the carpal ligament elicits a normal response in comparison to the segment of nerve across the carpal tunnel. In 100 hands of 50 normal adults, palmar stimulation of the median sensory fibers at 7 cm was compared to that at the wrist (14cm). Mean values for latency, amplitude, and duration were obtained, and palm/wrist ratios were calculated. Fifteen patients with CTS and 6 with underlying peripheral neuropathy were studied. This technique is useful for diagnosing early CTS and also for identifying an underlying mild peripheral neuropathy, eg, in diabetes mellitus.

Central somatosensory conduction after head injury

In 94 patients with head injuries, conduction between the lower brainstem and the cerebral cortex was studied by recording evoked potentials from the scalp and neck following stimulation of the median nerves. A conduction time 3 SD or more above the normal mean (5.74 +/- 0.46 msec) or the absence of an evoked potential over one or both hemispheres was considered abnormal. During successive periods in the first 35 days after injury, the evoked potentials correlated with the outcome (classified as good or not good) in 75 to 84% of patients. Within 3 1/2 days the outcome was correctly predicted in 38 of 49 patients (78%). Six of the 7 surviving patients with persistent asymmetries of the cerebral evoked potentials remained hemiplegic. Serial studies over one year showed that both conduction time and amplitude recovered exponentially over many months, but differences persisted between the patients who made a good recovery and those who remained disabled.

Comparison of orthodromic and antidromic sensory nerve conduction velocity measurements in the carpal tunnel syndrome

Orthodromic and antidromic nerve conduction velocities were determined in sensory median nerve fibres from digit to palm and from palm to wrist in patients with the carpal tunnel syndrome. In a large number of subjects the carpal tunnel syndrome could be detected only when the palm-to-wrist segment was investigated. Comparison of the results of the corresponding orthodromic and antidromic nerve conduction velocity measurements along the different segments revealed no significant disadvantages for the antidromic method. This technique should be given preference to the orthodromic method since it is easier.

The results of nerve grafting in the wrist and hand

To evaluate the usefulness of nerve grafting we studied 38 patients having 11 median, 7 ulnar, and 33 digital nerve grafts. Group funicular (interfascicular) grafting using magnification was performed in all patients. We followed 12 patients with 8 median and 5 ulnar nerve grafts for at least one year and 18 patients with 27 digital nerve grafts for at least six months. Medical Research Council criteria were used for evaluation of nerve function. Results in our patients and in previously reported patients having nerve grafting or repair were compared. Sensory function following ulnar nerve grafting was significantly better than that following nerve repair. Sensory function following median and digital nerve grafting was as good as that following nerve repair. Motor function following ulnar nerve grafting was as good as that following nerve repair. Previously reported patients having median nerve repairs or grafts had significantly better motor function than our patients.

Myelinated fibers of the deep branch of the ulnar nerve at the wrist in bonnet monkeys (Macaca radiata) and some of its branches to the hand

In order to estimate the peripheral nervous correlates concerning the motor performance of the hand, the myelinated fibers of the deep ulnar nerve and some of its branches to the intrinsic muscles of the monkey (Macaca radiata) hand have been enumerated and their caliber spectra plotted. The content of the myelinated sensory fibers in the deep ulnar nerve was found to be 70% of the total. This high figure is attributable to the fact that 25-50% of the myelinated fibers in the deep ulnar nerve are destined to innervate the joints of the hand. Approximately 50% of the myelinated fibers in nerves to the intrinsic muscles of the hand were sensory.

Ratio between the amplitude of sensory evoked potentials at the wrist in both hands of left-handed subjects

Maximum sensory conduction velocity, duration and amplitude of the sensory evoked potentials at the wrist on stimulating digits 1, 2, 3 and 5, were determined bilaterally in 21 left-handed subjects with an age range from 6 to 47 years. The amplitude of the sensory evoked potential at the wrist was larger in the right hand. This asymmetry is the reverse of the one previously observed in right-handed infants and adults. It could be physiological and suggests a difference in density of sensory innervation between the two hands. Asymmetry of sensory innervation can be helpful in the study of hand dominance.

Funicular orientation by electrical stimulation and internal neurolysis in peripheral nerve suture

Eleven peripheral nerve lacerations around the wrists of ten patients were treated with funicular suture or nerve graft. In three freshly lacerated nerves funicular orientation could be made only by electrical stimulation to both cut ends. The electrophysiological method was also utilised to obtain funicular orientation of a proximal stump in eight old nerve lacerations. However, funicular orientation of the distal stump of old lacerations, which was not responsive to electrical stimulation, was performed anatomically by internal neurolysis from a terminal branching area up to a distal stump. By six months after the operation, motor and sensory functions of the patients with funicular suture had recovered to an excellent degree with rapid reinnervation.