Evaluation of the lower motor neuron integrity of upper extremity muscles in high level spinal cord injury

PURPOSE

To evaluate the lower motor neuron (LMN) integrity of upper extremity muscles of persons with high tetraplegia (C1-C4) in order to determine muscles available for stimulation.

METHODS

Fourteen subjects (23 arms) were evaluated for LMN integrity. Muscles that elicited a functional response (grade 3 or better) to surface electrical stimulation were considered to have intact LMN and good candidates for FES. Strength-duration (S-D) curves were generated on muscles that showed weak (less than grade 3) or no response to surface stimulation. Muscles were considered denervated if S-D curves were discontinuous or depicted steep, increasing amplitude for pulse durations greater than 1 m.

RESULTS

Muscles for grasp and release had intact LMN in 19 of 23 (83%) arms. The wrist extensors and flexors and pronator were excitable in 17 (74%), 20 (87%) and 19 (83%) arms, respectively. The supinator demonstrated LMN lesion in 80% of the arms. Over 90% of the biceps muscles were unresponsive to electrical stimulation and 85% and 87% of the deltoid and supraspinatus muscles, respectively, were not electrically excitable. The latissimus dorsi and triceps muscles were typically innervated (78% and 91%, respectively) and slightly more than half (52%) of the pectoralis major muscles were excitable.

CONCLUSION

These data suggest that application of FES in high tetraplegia for hand and arm function would require augmentation because of the inability to stimulate the elbow flexors, deltoid and rotator cuff muscles. These data also show that several paralyzed proximal muscles with intact LMN that have been historically transferred to address shoulder paralysis in other patient populations are available for transfer and stimulation in the population with high level spinal injuries.

Patterned ballistic movements triggered by a startle in healthy humans

1. The reaction time to a visual stimulus shortens significantly when an unexpected acoustic startle is delivered together with the 'go' signal in healthy human subjects. In this paper we have investigated the physiological mechanisms underlying this effect. If the commands for the startle and the voluntary reaction were superimposed at some level in the CNS, then we would expect to see alterations in the configuration of the voluntary response. Conversely, if the circuit activated by the startling stimulus is somehow involved in the execution of voluntary movements, then reaction time would be sped up but the configuration of the motor programme would be preserved. 2. Fourteen healthy male and female volunteers were instructed to react as fast as possible to a visual 'go' signal by flexing or extending their wrist, or rising onto tiptoe from a standing position. These movements generated consistent and characteristic patterns of EMG activation. In random trials, the 'go' signal was accompanied by a very loud acoustic stimulus. This stimulus was sufficient to produce a startle reflex when given unexpectedly on its own. 3. The startling stimulus almost halved the latency of the voluntary response but did not change the configuration of the EMG pattern in either the arm or the leg. In some subjects the reaction times were shorter than the calculated minimum time for processing of sensory information at the cerebral cortex. Most subjects reported that the very rapid responses were produced by something other than their own will. 4. We conclude that the very short reaction times were not produced by an early startle reflex adding on to a later voluntary response. This would have changed the form of the EMG pattern associated with the voluntary response. Instead, we suggest that such rapid reactions were triggered entirely by activity at subcortical levels, probably involving the startle circuit. 5. The implication is that instructions for voluntary movement can in some circumstances be stored and released from subcortical structures.

[Compression of the palmar cutaneous branch of the median nerve at the wrist]

OBJECTIVE

To study the compression factor and clinical manifestation of the compression of the palmar cutaneous branch of the median nerve.

METHODS

Anatomic study was done on both sides of 2 cadavers and 6 cases of hand injury in the debridement, the origin, course, branch of the palmar cutaneous branch of the median nerve were observed. From 1995 to 1998, 12 patients of compression of the palmar cutaneous branch were treated by local blockade injection. Among them, there were 8 males and 4 females, aged from 23 to 65 years and the course of disease ranged 3 to 12 months.

RESULTS

The palmar cutaneous branch of the median nerve was (1.3 +/- 0.1) mm in diameter, it could be pulled when the wrist dorsi-extension. All cases showed good recovery of hand function and no recurrence after 4 to 12 months follow-up.

CONCLUSION

The palmar cutaneous branch compression syndrome is closely related to the local anatomy. The diagnosis is definite according to the clinical symptoms and signs, and local blocking is effective on the most patients.

Intraneural synovial sarcoma of the median nerve

Intraneural synovial sarcomas are extremely rare in the main nerve trunks of the upper limb. We report on a 16-year-old youth who presented with a painless mass on the flexor aspect of the wrist with the clinical appearance of a ganglion. At operation there was a tumour of the median nerve that was shown on histology to be an intraneural synovial sarcoma.

Conduction block in carpal tunnel syndrome

Wrist extension was performed in six healthy subjects to establish, first, whether it would be sufficient to produce conduction block and, secondly, whether the excitability changes associated with this manoeuvre are similar to those produced by focal nerve compression. During maintained wrist extension to 90 degrees, all subjects developed conduction block in cutaneous afferents distal to the wrist, with a marked reduction in amplitude of the maximal potential by >50%. This was associated with changes in axonal excitability at the wrist: a prolongation in latency, a decrease in supernormality and an increase in refractoriness. These changes indicate axonal depolarization. Similar studies were then performed in seven patients with carpal tunnel syndrome. The patients developed conduction block, again with evidence of axonal depolarization prior to block. Mild paraesthesiae were reported by all subjects (normals and patients) during wrist extension, and more intense paraesthesiae were reported following the release of wrist extension. In separate experiments, conduction block was produced by ischaemic compression, but its development could not be altered by hyperpolarizing currents. It is concluded that wrist extension produces a 'depolarization' block in both normal subjects and patients with carpal tunnel syndrome, much as occurs with ischaemic compression, but that this block cannot be altered merely by compensating for the axonal depolarization. It is argued that conduction slowing need not always be attributed to disturbed myelination, and that ischaemic compression may be sufficient to explain some of the intermittent symptoms and electrodiagnostic findings in patients with carpal tunnel syndrome, particularly when it is of mild or moderate severity.

Sensory and mixed nerve action potential temporal dispersion in median neuropathy at the wrist

This retrospective pilot study was undertaken to help determine the usefulness of measuring sensory nerve action potential and mixed nerve action potential temporal dispersion in median neuropathy at the wrist (MNW; i.e., carpal tunnel syndrome). The records were reviewed for 34 patients who were referred to an electrodiagnostic medicine laboratory with normal antidromic median sensory nerve action potential (recording from the index finger), median transcarpal mixed nerve action potential, and ulnar transcarpal mixed nerve action potential peak distal latencies (NO group) and 29 patients with prolongation (>2.2 ms) of the left median transcarpal mixed nerve action potential peak distal latency or relative prolongation of this response (>0.4 ms) compared with the ipsilateral normal ulnar transcarpal mixed nerve action potential peak distal latency (MNW group). By using the time difference between onset and negative peak as a measure of waveform temporal dispersion, mean +/- standard deviation of the median transcarpal mixed nerve action potential time difference for the MNW group (0.57 +/- 0.15 ms) was found to be greater than the NO group (0.44 +/- 0.09 ms; P < 0.01). No statistically significant differences were found for the median sensory nerve action potential time difference between the two groups or between the subgroup of MNW patients with concurrent prolongation of the median sensory nerve action potential peak distal latency and the NO group. These findings suggest that increased median transcarpal mixed nerve action potential temporal dispersion may occur in association with median transcarpal mixed nerve action potential peak distal latency prolongation in MNW. The small magnitude of this increase, however, makes the clinical usefulness of this observation unclear.

Complete avulsion of the distal posterior interosseous nerve during wrist arthroscopy: a possible cause of persistent pain after arthroscopy

A case of avulsion of the distal posterior interosseous nerve during wrist arthroscopy is presented. Surgeons unaware of this entity may attribute persistent middorsal wrist pain to the underlying disease rather than to iatrogenic damage to the distal posterior interosseous nerve.

[Ulnar nerve compression in the area of the wrist]

Clinical investigation precisely determines the localization of ulnar nerve entrapment in Guyon's canal. The cause of compression can be due to internal (tumor, distal fibrous arch or proximal ligament arcade, nerve or muscle anomalies) or external influences (ulnar neuropathy of cyclists, thrombosis of ulnar artery by hypothenar hammer syndrome, fractures of pisiform or hook of hamate). Treatment involves splitting the roof of Guyon's canal, the ligaments or muscle anomalies, and excision of a tumor.

Transfer of flexor carpi ulnaris branch of the ulnar nerve to the pronator teres nerve: histomorphometric analysis

Partial median-nerve injury high in the upper extremity, resulting from brachial plexus neuritis or trauma, can affect the pronator teres muscle and result in the inability to pronate the forearm. A nerve transfer from an ulnar nerve-innervated branch to the flexor carpi ulnaris (FCU) muscle to the branch to the pronator teres (PT) is an attractive option in this clinical scenario. This study, a histomorphometric analysis of nine cadaver specimens harvested at the proposed FCU branch to PT branch transfer site, demonstrates sufficient similarities between the two branches in total number of nerve fibers (371.6 with SEM 35.1, and 361.9 with SEM 47.1; p = 0.87) and nerve cross-sectional area (122,181 microm2 with SEM 14,546 microm2, and 142,492 microm2 with SEM 19,633 microm2; p = 0.42), to predict a functional transfer result. In addition, clinical application of this transfer resulted in functional pronation strength of M4+.

Carpal tunnel syndrome involving unaffected limbs of stroke patients

BACKGROUND AND PURPOSE

Stroke-induced hemiparesis involving the arm and hand results in regular, repeated overuse of the opposite hand and wrist. Because repetitive hand and wrist movement is a common cause of carpal tunnel syndrome (CTS), we examined the nonparetic upper limb in stroke patients for evidence of CTS.

METHODS

We measured bilaterally sensory nerve conduction velocity (SNCV), motor nerve conduction velocity (MNCV), sensory nerve action potentials (SNAP) at the wrist, palm-to-wrist distal sensory latency (DSL), palm-to-wrist SNAP, compound motor action potentials (CMAP), and distal motor latency (DML) in stroke patients and control subjects. Controls were right-handed, >/=65 years old, lucid, independent in their activities of daily living, and had no disease known to cause CTS. Stroke patients were divided into a functioning hand group (n=61) and a disused hand group (n=71). All patients had hemiplegia.

RESULTS

Tinel's sign was observed on the nonparetic side in 57.7% of patients with a disused hand and in 31.1% of those with a functioning hand. All electrophysiological indices were significantly more abnormal on the nonparetic side than on the hemiparetic side or in controls. Patients with a disused hand showed greater abnormality on the nonparetic side in SNCV, SNAP, palm-to-wrist DSL, DML, and CMAP than patients with a functioning hand.

CONCLUSIONS

Overuse of the nonparetic hand and wrist of the nonparetic side may result in CTS in stroke patients, especially when the paretic hand is not functional. Wrist splinting or other prophylactic treatments beginning soon after stroke might help to prevent CTS.

Sensitive median-ulnar motor comparative techniques in carpal tunnel syndrome

We describe two modified methods for median-to-ulnar motor conduction comparison in the diagnosis of median neuropathy at the wrist: the median-thenar to ulnar-thenar latency difference (TTLD), and the median-thenar to ulnar-hypothenar latency difference (THLD). We also describe an F-wave ulnar-to-median comparative test, the F-wave latency difference (FWLD). The abnormal cutoffs based upon 34 normal controls are: TTLD, 0.8 ms; THLD, 1.2 ms; FWLD, 0.6 ms. In 50 patients (79 hands) with clinically defined carpal tunnel syndrome and electrophysiological evidence of median neuropathy at the wrist (based upon a prolonged median nerve palm-wrist latency), the diagnostic sensitivities were: 95-98%, 85-88%, and 75-78%, respectively. These tests are therefore highly sensitive. They are easily performed and require minimal additional effort to incorporate into commonly used clinical electrodiagnostic routines. They may be advantageous when a concomitant polyneuropathy is present, and they may also help avoid technical pitfalls and aid in identification of anatomic variants.

Origin of the "N10" stationary-field potential after median nerve stimulation

The scalp far-field potentials after median nerve stimulation at the wrist consist of P9, P11, P13, and P14 positive components. Earlier, Emerson et al. (1984) identified the "N10" negative potential in-between the P9 and P11 and claimed that this was not merely a passive return to the baseline after the P9 positive deflection but a distinct component reflecting a proximal brachial plexus volley. They thought N10 was a far-field potential having widespread distribution with a fixed latency. In this study we found that N10 was of higher amplitude after median nerve stimulation at the elbow than after stimulation at the wrist. Indeed the N10 latency was fixed from the lower anterior neck to the scalp, and its amplitude was maximum at the anterior lower neck. The latency of N10 was about 0.3 milliseconds longer than the Erb's potential and 0.15 milliseconds longer than the potential recorded from the lateral neck on the side of stimulation. The N10 amplitude increased in parallel with increased stimulus intensity. In order to explore the origin of the N10 stationary field potential, we designed a paired stimuli paradigm applied to the wrist (S1) and to the elbow (S2). The interstimulus interval between S and S2 was adjusted so that the timing of S2 was immediately after the traveling impulse produced by the S1 stimulus as it passed through the S2 stimulus site. This technique allowed stimulation of the anterior interosseous nerve selectively at the elbow while the median nerve originating from the wrist was undergoing refractory period. The response of (S1 + S2) - S1 showed only the N10 with absence of cervical and cortical responses, implying that N10 was activated, predominantly by the interosseous nerve, i.e., an antidromic motor volley, when the median nerve was stimulated at the elbow.

Sensory nerve conduction velocity is inversely related to axonal length

It was found that the axonal length was inversely related to motor conduction velocity (CV). However, it is not clear that sensory CV is inversely related to axonal length. The nerve lengths of the median sensory fascicles from the C6 and C7 intervertebral foramen to the digital branches of the thumb and middle finger were compared in ten cadavers. Sixty healthy subjects (24 men, 36 women; mean age 35, range 24-54 years) had median sensory CV testing. The median sensory nerve action potentials were obtained antidromically in the thumb and middle finger with wrist and elbow. The CVs across the forearm for the thumb and the middle finger fascicles were then calculated. It was found that the nerve length of C7 was longer than C6 with a difference of 3.6 +/- 0.6 cm. The mean forearm CV for the median sensory axons innervating the middle finger (60.0 +/- 3.9 m/s) was slower than the CV for the median sensory axons innervating the thumb (61.4 +/- 4.1 m/s,p = 0.0012). These results demonstrate that sensory CV is slowed by 3.9 m/s per 10 cm of axon length. This study confirms that the inverse relation of CV and axonal length reported in motor axons also applies to the sensory nerves.

[Carpal tunnel syndrome in childhood. A case of early onset]

INTRODUCTION

The carpal tunnel syndrome (CTS) is the commonest neuropathy due to compression to be seen in adults. There are very few cases in the literature referring to patients of paediatric age, particularly those under ten years old. Most of these young patients had a metabolic disorder (mucopolysaccharidosis (MPS) or mucolipidosis (ML). In fact, as many as 90% of the MPS had CTS, sometimes subclinically. This syndrome is caused by compression of the median nerve at the level of the carpal tunnel, to which multiple factors may contribute, both local and systemic, as reviewed in this paper. The clinical findings differ from those in adults, but the appearance of suggestive symptoms and signs should make one suspect the condition and request an electromyographic study (EMG) which would be diagnostic.

CLINICAL CASE

We describe the case of a five year old girl, with a clinical history suggesting the presence of a carpal tunnel syndrome for 12 months and characterized by paraesthesia and limitation of flexon-extension movements of the fingers of the affected hand, with pain on movement. The symptoms appeared on waking in the morning, gradually improved as the day advanced and became bilateral over a period of six months. The diagnosis was confirmed by EMG and MR helped to clarify the aetiology.

CONCLUSION

The interesting aspect of this article is the youth of the patient, the absence of known etiological factors and the presence of tenosynovitis detected on MR as has been described in some idiopathic/familial forms.

[Section of the median nerve at the wrist]

INTRODUCTION

The usefulness of neurophysiological studies of peripheral nerves depends basically on an understanding of the physiopathology, especially of the evolutionary aspects of the phenomena of reinnervation.

CLINICAL CASE

We present the case of a girl with complete section and immediate anastomosis of the two cut ends of the median nerve, at the wrist. Sixty two days later she had unmistakable signs of reinnervation (response in the thenar eminence to an electrical stimulus of 300 uV in amplitude and 42 ms in latency, with denervation and reinnervation on the EMG of the abductor pollicis brevis muscle).

DISCUSSION

The findings in our patient show a rather faster rate of nerve regeneration than is usually accepted in the literature. This may have been due to suitable selection of some of the parameters of the neurophysiological study, such as time of analysis and sensitivity, which when not satisfactory may lead to an impression of failure or delay in reinnervation.

Dynamic response of human muscle spindle afferents to stretch during voluntary contraction

1. The response of twenty-eight human muscle spindle afferents from m. extensor carpi radialis brevis to large amplitude ramp stretch and release at the wrist joint was recorded. The dynamic index was calculated as the difference in firing rate between that just before the end of stretch and that during the subsequent static phase of stretch. The value during steady voluntary contraction was compared with that during relaxation. 2. In twenty-three primary afferents, the dynamic index increased in eleven and decreased in twelve afferents with a range of -8 to +25 impulses s-1. In five secondary afferents the change was less than 2 impulses s-1. 3. The primary afferents abruptly stopped firing when the stretch was released in the relaxed muscle. This cessation was prevented during contraction in seventeen primary afferents. 4. The results suggest the presence of dynamic and static fusimotor actions on the human muscle spindles during voluntary contraction.

Median and ulnar nerves in the hand

There are a multitude of different testing techniques to evaluate the median and ulnar nerves for abnormalities at the wrist and hand. The electrodiagnostician should be able to use his or her knowledge of anatomy, history, physical examination, and electrophysiology to accurately diagnose common median and ulnar nerve dysfunction in the distal upper extremity.

Anatomic considerations in evaluation of the proximal ulnar nerve

Knowledge of general ulnar anatomy aids in the understanding of the possible site of ulnar nerve entrapment and the rationale for differential diagnosis possibilities. Understanding of internal nerve topography sheds light on reasons for ulnar nerve susceptibility at the elbow region and offers an explanation for the sparing of forearm muscles in ulnar neuropathy at the elbow. Dynamic anatomy or biomechanics of the elbow help elucidate the pathophysiology of ulnar nerve compression at the elbow. The anatomy interface with electrodiagnosis illustrates rationale for particular methods employed and particular tests used in evaluating the ulnar nerve. Electrodiagnostic testing enhances localization of ulnar nerve lesions, excludes other causes in the differential diagnosis, and may aid with surgical selection.

Orthodromic inching test in mild carpal tunnel syndrome

The Orthodromic inching test of the median nerve at wrist was performed on the dominant wrist of 80 controls and of 100 patients with mild carpal tunnel syndrome defined by the presence of clinical features and normal classical electrodiagnostic tests. In controls the mean conduction delay per centimeter (CD/cm) was 0.184ms and was slightly higher inside than outside the carpal tunnel; the maximal CD/cm (MCD/cm) was never greater than 0.34ms (mean 0.247). In patient the MCD/cm was 0.36 ms or more in 96 patients. This abnormality was located within the carpal tunnel in 92% of cases. Outside the entrapment site CD/cm values remained normal and similar to those found in the controls. On the whole, this results in an overall specificity of 100% and sensitivity of 96% for the Orthodromic inching test.

Neuroma of the distal posterior interosseous nerve. A cause of iatrogenic wrist pain

We describe four women and two men who had persistent wrist pain and reduced function after minor operations on the dorsum, usually for ganglia. They had diffuse pain and paraesthesia over the dorsum of the wrist, thumb, index and middle fingers, which was worse and different from that before operation. They all had temporary relief of symptoms after block of the posterior interosseous nerve with bupivacaine. Later, excision of the terminal branches of the nerve at the wrist cured three patients completely and gave marked improvement in the other three, with no complications. Great care is required at operations on the dorsum of the wrist, but pain from a neuroma can be relieved by local excision.

Neurovascular problems in the forearm, wrist, and hand

This article attempted to summarize the most common neurovascular injuries of the upper extremity, particularly the forearm, wrist, and hand. Although these injuries are rarely encountered in athletes, their pathology and treatment must be understood by the treating physician. Failure to recognize these injuries in a timely manner can lead to delay in diagnosis and weeks or months of lost participation by the athlete. The sports medicine physician must be aware of the potential risk for injury to the neurovascular structures, particularly in the athlete exposed to repetitive use or impact of the upper extremity. Timely recognition, diagnosis, and treatment will avoid the potential risk for permanent injury.

Normal values of F wave in upper extremities of 50 healthy individuals in Iran

F wave latency has been shown to be a valuable method in evaluation of a variety of neurologic disorders. We measured F wave values in 50 healthy individuals in Shiraz. Maximum normal F wave latency for median nerve was 25.7 ms for women and 28.5 ms for men with stimulation at the wrist. It was 23 ms for women and 25 ms for men with stimulation at the elbow. Maximum normal F wave latency for ulnar nerve was 26.45 ms for women and 28.9 ms for men with stimulation at the wrist. It was 23.1 ms for women and 25.3 ms for men with stimulation at the elbow. Maximum normal difference in F wave latency between right and left upper extremities with stimulation at the wrist for total group was 2.2 ms for median nerve and 2.4 ms for ulnar nerve. Maximum normal difference in F wave latency between median and ulnar nerve in an extremity with stimulation at the wrist for total group was 2.7 ms. There was statistically significant difference in F wave latency between women and men.

The detailed anatomy of the palmar cutaneous nerves and its clinical implications

The forearms and hands of 40 fresh-frozen cadavers were dissected under the microscope to study the palmar cutaneous branch of the median nerve (PCBm) and the palmar cutaneous branch of the ulnar nerve (PCBu). Branches of the PCBm innervating the scaphoid were typically found, but in no specimen did we find a 'typical' cutaneous branch of the ulnar nerve. According to our findings, standard incisions for open carpal tunnel release carry a significant risk of damaging branches of the PCBm or PCBu. The chance of injury to these sensory nerves can be minimized by using a short incision in the proximal palm or a twin incision approach, which we describe. Because the PCBm is closely associated with the ulnar side of the flexor carpi radialis (FCR) sheath, this sheath should be opened on the radial side during harvest of the FCR tendon for transfer. When transferring the palmaris longus tendon, it should be cut proximal to the distal wrist crease to avoid possible damage to the PCBm.