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.

Neuromuscular stimulation for upper extremity motor and functional recovery in acute hemiplegia

BACKGROUND AND PURPOSE

The purpose of this study was to assess the efficacy of neuromuscular stimulation in enhancing the upper extremity motor and functional recovery of acute stroke survivors.

METHODS

Forty-six stroke survivors admitted to an inpatient rehabilitation unit were randomly assigned to receive either neuromuscular stimulation or placebo. Twenty-eight subjects completed the study. The treatment group received surface neuromuscular stimulation to produce wrist and finger extension exercises. The control group received placebo stimulation over the paretic forearm. All subjects were treated 1 hour per day, for a total of 15 sessions. Outcomes were assessed in a blinded manner with the upper extremity component of the Fugl-Meyer Motor Assessment and the self-care component of the Functional Independence Measure at pretreatment, after treatment, and at 4 and 12 weeks after treatment.

RESULTS

The treatment subjects and control subjects had comparable baseline characteristics. Parametric analyses revealed significantly greater gains in Fugl-Meyer scores for the treatment group after treatment (13.1 versus 6.5; P=0.05), at 4 weeks after treatment (17.9 versus 9.7; P=0.05), and at 12 weeks after treatment (20.6 versus 11.2; P=0.06). Functional Independence Measure scores were not different between groups at any of the time periods (P>0.10).

CONCLUSIONS

Data suggest that neuromuscular stimulation enhances the upper extremity motor recovery of acute stroke survivors. However, the sample size in this study was too small to detect any significant effect of neuromuscular stimulation on self-care function.

Ulnar nerve entrapment at the wrist: cases from a hand surgery practice

BACKGROUND

Eight patients with 11 instances of wrist-level ulnar nerve entrapment, a fairly uncommon compression syndrome, were identified in a hand surgery practice from 1992 through 1996.

METHODS

Presentations, causes, and surgical outcomes were examined, and the pertinent literature was reviewed.

RESULTS

All eight patients had extrinsic, nonidiopathic compression of the ulnar nerve caused by tumor, vascular disease, anomalous muscle development, or a tight fibrous arch at the origin of the flexor digiti minimi. In all cases, sensory symptoms resolved with removal of the cause of ulnar nerve compression.

CONCLUSIONS

These cases serve to remind physicians that not every instance of numbness and tingling in the hand represents carpal tunnel syndrome. Careful clinical examination may not only localize compression of the ulnar nerve at wrist level but also may reveal its etiology. Some causes of ulnar compressive neuropathy, however, are apparent only with surgical exploration.

Muscular sense is attenuated when humans move

1. Muscle receptors play an important role in our conscious perception of movement, but there are no published accounts of our ability to detect their signals during different motor tasks. The present experiments introduce a method to test muscular sense when humans move. 2. Muscle receptors were excited by an electrically induced twitch of the right extensor carpi ulnaris muscle. The muscle was stimulated via percutaneously inserted intramuscular electrodes or using surface stimulation through anaesthetized skin. Muscular sense was represented by the ability to detect the twitch and was compared between various tasks and stationary control trials. 3. Three hertz voluntary wrist movements significantly attenuated muscular sense to 37 % of control. This velocity-dependent attenuation was present over a range of twitch amplitudes suggesting it does not simply reflect a masking of low intensity stimuli. Perceptual ratings of twitch amplitude during fast imposed passive movements were reduced by 40 %, though this did not quite reach statistical significance. However, perceptual ratings of twitches evoked up to 2 s after the termination of the passive movements were significantly different from control. 4. Reaching with the stimulated, but not the contralateral, arm also significantly reduced muscular sense (to 40 %). 5. Attenuation to 58 % of control during cyclic stretching of the skin on the dorsum of the hand showed that signals from peripheral receptors may play a role. Attenuation prior to a single wrist flexion movement indicated that central sources can also contribute. 6. The results are consistent with current findings of a general attenuation of sensory feedback during movement and raise questions regarding the role of muscular sense in movement control.

Event-related beta synchronization after wrist, finger and thumb movement

Pre-movement event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were studied in a group of normal subjects during voluntary thumb, index finger and wrist movement. The band power time courses were computed for the upper alpha band (10-12 Hz) and for two frequency bands in the range of beta (16-20 Hz and 20-24 Hz). While a similar mu ERD was found during motor preparation for the 3 movement tasks, significant differences concerning beta synchronization were observed after movement off set. The contralateral percentage beta increase (ERS) was significantly larger in gross movements of the wrist as compared to index finger and thumb movements, which is discussed under the assumption of a cumulative effect. Summarizing, pre-movement desynchronization seems relatively independent of the forthcoming type of movement, whereas the post-movement beta synchronization might depend on the activated muscle mass.

The influence of acute normovolemic hemodilution on the dose-response and time course of action of vecuronium

To evaluate the influence of acute isovolemic hemodilution on the dose-response and time course of action of vecuronium, we studied 60 adult patients with and without hemodilution during surgery. The patients with hemodilution underwent major elective plastic surgery with an anticipated surgical loss of more than 600 mL. Anesthesia was induced with thiopental 4-6 mg/kg and fentanyl 2-4 microg/kg i.v. and was maintained with 60% nitrous oxide in oxygen. Further increments of thiopental 2 mg/kg or fentanyl 2 microg/kg were given as required. Acute isovolemic hemodilution in the hemodilution group was induced by drainage of venous blood and an i.v. infusion of lactated Ringer's solution and 6% dextran, during which hematocrit and hemoglobin decreased from 45.7% to 26.2% and from 148.5 g/L to 90.2 g/L, respectively. Neuromuscular function was assessed mechanomyographically with train-of-four stimulation at the wrist every 12 s, and the percent depression of T1 response was used as the study parameter. The dose-response relationships of vecuronium in the two groups were determined by using the cumulative dose-response technique. The results showed that during hemodilution, the dose-response curve of vecuronium was shifted to the left in a parallel fashion, and the potency of vecuronium was increased. There were significant differences in the 50%, 90%, and 95% effective doses between the two groups. After the i.v. administration of vecuronium 80 microg/kg, vecuronium-induced neuromuscular block was significantly longer in the patients with hemodilution than in the control patients. The duration of peak effect, clinical duration, recovery index, and total duration in the hemodilution patients were significantly different from those in the control patients. We conclude that hemodilution induces significant changes in the pharmacodynamics of vecuronium.

IMPLICATIONS

We found that patients with hemodilution were 20% more sensitive to vecuronium and had a longer duration of action after the administration of the same dose than the controls. This should be taken into account when vecuronium is used as a muscle relaxant during acute hemodilution.

Selective activation of human cortical area V5A by a rotating visual stimulus in fMRI; implication of attentional mechanisms

The human homologue of area V5A of rotation-selective cells in the monkey medial superior temporal area (MST) was identified using functional magnetic resonance imaging (fMRI). It was located within the border region of occipito-temporo-parietal cortex, in four of 10 subjects on both sides, and on the right or left side in three subjects each. The stimulus was a black-and-white sine-modulated windmill presented either stationary or in rotation phases of 1 s duration. Areas V1-V3 did not show up with this paradigm. Focusing attention by mentally counting the number of rotation phases ensured high signal intensity in V5A, whereas moving attention away by counting electric stimuli to the wrist diminished it despite persistent fixation of gaze to the centre of the windmill.

The role of ulnar nerve transposition in ulnar nerve repair: a cadaver study

Ulnar nerve transposition at the elbow is recommended to diminish nerve gaps during neurorrhaphy. We undertook a cadaver study to determine the gap distance that can be overcome by subcutaneous transposition at the elbow, evaluating lacerations 2.0 cm distal to the medial epicondyle and 2.0 cm proximal to the wrist crease. With a 100-g load on each nerve stump, gaps that could be overcome were measured before and after transposition in different elbow and wrist positions. For the distal forearm lacerations, wrist position significantly affected nerve gap, while transposition and elbow position did not. Nerve gap was significantly reduced by approximately 11 mm with wrist flexion from 0 degrees to 45 degrees. For proximal forearm lacerations, gap distance was significantly affected by transposition and was dependent to a greater extent on the interaction between transposition and elbow position, with wrist position having no effect. A clinically relevant scenario for the proximal laceration compared the pretransposition gap with the elbow and wrist at neutral with the posttransposition gap with the elbow and wrist flexed. Posttransposition gap reduction, with elbow and wrist flexion at 45 degrees, was approximately 9 mm and was not significant. To span a gap near the elbow, we estimate that more than 45 degrees of elbow flexion is required.

[Functional neuroanatomy of the radial nerve in the region of the long wrist and finger joint extensors and the supinator groove]

Basing on electrophysiological data measured by us we studied the course of the radial nerve or its motoric branches with regard to anatomically conditioned bony contractions and their possible significance for pain experienced at the radial epicondyle of humerus, the pain being known under several synonymous designations. To differentiate between the various pathomechanisms discussed in the literature, we performed longitudinal and transversal dissections on a total of 40 cadaveric arms. We found as constant variations to the topographic anatomy published in the standard literature a regularly extended and (in relation to the other muscles we examined) exposed course of the nerve branch proceeding towards the m. extensor carpi radialis brevis. As the only long wrist extensor muscle this is innervated in most cases from the superficial end branch of the radial nerve. The origin of the muscle projected regularly over the common aponeurosis of the extensor tendon and delimitated in most of the preparations the distal end of the tunnel of the deep radial nerve. Since the deep radial branch and the muscular branches parallel to that branch cross this part of the tendon at an obtuse angle we believe that the repeatedly discussed possibility of a dynamic nerve compression without structural influences is the triggering mechanism for the observed nerve damage.

Corticospinal excitability modulation during mental simulation of wrist movements in human subjects

Motor evoked potentials (MEPs) to magnetic transcranial stimulation (TCS) were simultaneously and bilaterally recorded from flexor carpi radialis (FCR) and extensor communis digitorum (ECD) muscles in seven healthy and trained subjects. Latencies and amplitudes characteristics of MEPs were investigated under the following randomised conditions: muscular and mental relaxation; mental simulation, during absolute muscular relaxation, selective flexion or extension of the right or left wrist muscles; arithmetical calculation with muscular relaxation. Unspecific, diffuse facilitatory effects on MEPs amplitude were induced by mental non motor activity (arithmetical calculation). A further specific and lateralised amplitude potentiation on the agonist muscle acting as 'prime mover' for the mentally simulated movement was consistently found in all the subjects, without significant latency changes. Inhibitory effects on antagonists were evident only in two subjects.

Overactivity of cervical premotor neurons in Parkinson's disease

OBJECTIVES

Cortical command to upper limb motor neurons is transmitted, in humans, not only through the monosynaptic corticomotor neuronal pathway, but also through cervical premotor neurons. Whether activity in this non-monosynaptic corticospinal pathway is modified in Parkinson's disease was explored.

METHODS

Ongoing EMG activity recorded in wrist extensors during tonic extension of the wrist is suppressed by a volley evoked by stimulating the superficial radial nerve. It has been shown that this cutaneous induced suppression is due to inhibition of transmission of the cortical command at a premotor neuronal level. By comparing the cutaneous induced EMG depression between 45 de novo parkinsonian patients and 23 age matched controls it has been possible to appreciate if and to what extent the "non-monosynaptic" part of the cortical command is modified in these patients.

RESULTS

At the early stage of the illness the EMG depression, reflecting the "non-monosynaptic" part of the cortical command, was bilaterally increased despite very asymmetric clinical status. When the duration of the disease was more than 36 months, EMG depression returned to its control level. No correlation was found between the amount of the EMG depression and parkinsonian symptoms before and after levodopa treatment.

CONCLUSION

Increase of the relative "non-monosynaptic" part of the cortical command could reflect a compensatory motor mechanism elaborated upstream from the motor cortex.

Ulnar nerve compression at the wrist secondary to anomalous muscles: a patient with a variant of abductor digiti minimi

Three patients with aberrant muscles passing through Guyon's canal are described. Each of the three patients experienced, among other symptoms, dysesthesias on the volar aspects of the little and ring fingers. The anomalous muscle in two of these patients arose from the antebrachial fascia just proximal to Guyon's canal, traveled through the canal, and inserted with the abductor digiti minimi muscle. This anomaly was bilateral in both patients. In the third patient the abductor digiti minimi muscle originated radially from the transverse carpal ligament, and this variant too was bilateral. Symptoms in each of the 3 patients resolved following surgery. Ulnar nerve compression at Guyon's canal is discussed and the literature is reviewed. Although anomalous muscles occur frequently in this location, the anatomic variant found in patient 3 has not yet been described in the literature.

Firing pattern of type-identified wrist extensor motor units during wrist extension and hand clenching in humans

1. Single motor unit activity was investigated in the extensor carpi radialis muscles during voluntary isometric contraction involving either the coactivation of the wrist agonist extensor muscles (wrist extension) or the coactivation of the wrist and finger antagonist extensor and flexor muscles (hand clenching). 2. The motor units were found to be activated at a similar level of motoneurone pool drive during both wrist extension and hand clenching, as indicated by the fact that the EMG activity at which they were recruited was practically the same in both cases (mean +/- S.D.: 20 +/- 26 and 21 +/- 25 mV, respectively). In addition, the net excitatory drive exerted on the motoneurones, as assessed from the mean interspike intervals, did not differ significantly between the two tasks (mean +/- S.D.: 104.57 +/- 17.24 and 103.01 +/- 16.26 ms, for wrist extension and hand clenching, respectively). 3. However, the discharge variability, in terms of the coefficient of variation of the interspike intervals, was slightly but significantly greater during hand clenching than during wrist extension (0.213 +/- 0.049 and 0.198 +/- 0.045, respectively). This increase involved all types of motor units, regardless of their contractile force. 4. We suggest that the greater motoneurone discharge variability observed during hand clenching may be attributable to an increase in the synaptic noise. This increase might be due to the activation of numerous afferent pathways mediating reciprocal interactions between antagonist motoneurone pools, as well as to the activation of hand cutaneous receptors that play a major role in the regulation of handling and gripping motor activities.

Distinctive abnormalities of facial reflexes in patients with progressive supranuclear palsy

Spontaneous and voluntary eyelid motility is often abnormal in patients with progressive supranuclear palsy. In contrast, their eyelid reflex responses are relatively preserved, and only those generated by an acoustic startle have been found absent or severely reduced. We hypothesized that, because of their relevant brainstem pathology, patients with progressive supranuclear palsy might have other brainstem reflex abnormalities which, on detection, could help with their neurophysiological characterization. In this study, we examined facial reflex responses in 14 patients with progressive supranuclear palsy, 12 patients with multisystem atrophy, 10 patients with Parkinson's disease, six patients with corticobasal ganglionic degeneration, 11 patients with various non-parkinsonian neurological illnesses and 10 normal subjects. EMG activity was simultaneously recorded from the orbicularis oculi and mentalis muscles following electrical stimulation of the median nerve at the wrist. Mentalis responses were obtained in two normal subjects and in all patients except one with Parkinson's disease, one with progressive supranuclear palsy and one with corticobasal ganglionic degeneration; there were no differences between groups of subjects regarding latency or peak amplitude. Orbicularis oculi responses were always present in control subjects and patients who exhibited mentalis responses, with the significant exception of patients with progressive supranuclear palsy, in whom only the response of mentalis was obtained. Blink-reflex responses to supraorbital nerve electrical stimuli were present at a normal latency and amplitude in all patients. An abnormally enhanced blink-reflex excitability recovery curve to paired stimuli was found in a similar percentage of patients with progressive supranuclear palsy, multisystem atrophy and Parkinson's disease, but in only two patients with corticobasal ganglionic degeneration. Patients with progressive supranuclear palsy have a functional involvement of circuits mediating orbicularis oculi responses to median nerve electrical stimuli, that is a distinctive feature with respect to other parkinsonian syndromes.

Synaptic connections from large afferents of wrist flexor and extensor muscles to synergistic motoneurones in man

Short-latency excitatory Ia reflex connections were determined between pairs of human wrist flexor and extensor muscles. Spindle Ia afferents were stimulated by either tendon tap or electrical stimulation. The activity of voluntarily activated single motor units was recorded intramuscularly from pairs of wrist flexor or extensor muscles. Cross-correlation between stimuli and the discharge of the motor units provided a measure of the homonymous or heteronymous excitatory input to a motoneurone. Homonymous motoneurone facilitation was generally stronger than that of the heteronymous motoneurones. The principal wrist flexors, flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU), were tightly connected through a bidirectional short-latency reflex pathway. In contrast, the extensor carpi ulnaris (ECU) and the extensor carpi radialis (ECR) did not have similar connections. ECU motoneurones received no short-latency excitatory Ia input from the ECR. ECR motoneurones did receive excitatory Ia input from ECU Ia afferents; however, its latency was delayed by several milliseconds compared with other heteronymous Ia excitatory effects observed. The wrist and finger extensors were linked through heteronymous Ia excitatory reflexes. The reflex connections observed in humans are largely similar to those observed in the cat, with the exception of heteronymous effects from the ECU to the ECR and from the extensor digitorum communis (EDC) to the ECU, which are present only in humans. The differences in the reflex organization of the wrist flexors versus the extensors probably reflects the importance of grasping.

[Clinical experiences with a new Wiedemann method of radial replacement operation]

Many modifications of tendon transfers have been described in the treatment of radial nerve palsy. Controversy persists over the muscles of choice to get the best results in motion of wrist and fingers. Patients with radial nerve palsy and treated by the method of Merle d'Aubigne in neurophysiological tests showed that the pronator teres did not work very well for extending the wrist. Thinking about the neurophysiologic principles it seemed that the flexor digitorum superficialis of the middle and ring fingers would make a better substitute for the wrist extension. From 1994 to 1997 four patients with radial nerve palsy had a transfer of the flexor digitorum superficialis tendons from the middle and ring fingers to the tendons of extensor carpi radialis longus and brevis additional the flexor carpi ulnaris and palmaris longus transfers. The functional recovery of two patients has been tested. The functional range of wrist motion of this two patients has been better than in patients with pronator teres transfers. It can be concluded that the new modification of tendon transfers is a good way of treatment of radial nerve palsy and should be done further.

Parkinsonism reduces coordination of fingers, wrist, and arm in fine motor control

This experiment investigates movement coordination in Parkinson's disease (PD) subjects. Seventeen PD patients and 12 elderly control subjects performed several handwriting-like tasks on a digitizing writing tablet resting on top of a table in front of the subject. The writing patterns, in increasing order of coordination complexity, were repetitive back-and-forth movements in various orientations, circles and loops in clockwise and counterclockwise directions, and a complex writing pattern. The patterns were analyzed in terms of jerk normalized for duration and size per stroke. In the PD subjects, back-and-forth strokes, involving coordination of fingers and wrist, showed larger normalized jerk than strokes performed using either the wrist or the fingers alone. In the PD patients, wrist flexion (plus radial deviation) showed greater normalized jerk in comparison to wrist extension (plus ulnar deviation). The elderly control subjects showed no such effects as a function of coordination complexity. For both PD and elderly control subjects, looping patterns consisting of circles with a left-to-right forearm movement, did not show a systematic increase of normalized jerk. The same handwriting patterns were then simulated using a biologically inspired neural network model of the basal ganglia thalamocortical relations for a control and a mild PD subject. The network simulation was consistent with the observed experimental results, providing additional support that a reduced capability to coordinate wrist and finger movements may be caused by suboptimal functioning of the basal ganglia in PD. The results suggest that in PD patients fine motor control problems may be caused by a reduced capability to coordinate the fingers and wrist and by reduced control of wrist flexion.

Positive force feedback control of muscles

This study was prompted by recent evidence for the existence of positive force feedback in feline locomotor control. Our aim was to establish some basic properties of positive force feedback in relation to load compensation, stability, intrinsic muscle properties, and interaction with displacement feedback. In human subjects, muscles acting about the wrist and ankle were activated by feedback-controlled electrical stimulation. The feedback signals were obtained from sensors monitoring force and displacement. The signals were filtered to mimic transduction by mammalian tendon organ and muscle spindle receptors. We found that when muscles under positive force feedback were loaded inertially, they responded in a stable manner with increased active force. The activation attenuated the muscle stretch (yield) that would otherwise occur in the absence of feedback. With enough positive force feedback gain, yield could actually reverse. This behavior, which we termed the affirming reaction, was reminiscent of the mammalian positive supporting reaction, a postural response elicited by contact of the foot with the ground. Muscles under positive force feedback remained stable, even when the loop gain (Gf) was set at levels of 2 or 3. In a linear system, if Gf > 1, instability occurs when the loop is closed. On further investigation, we found that Gf changed with joint angle: it declined as the load-bearing muscle actively shortened. We inferred that in closed-loop operation, the active muscles always shortened until Gf approached unity. In other words, the length-tension curve of active muscle ensures stability even when force-related excitation of motoneurons is very large. Concomitant negative displacement feedback reinforced and stabilized load compensation up to a certain gain, beyond which instability occurred. In further trials we included delays of up to 40 ms in the positive force feedback pathway, to model the delays recently described for tendon organ reflexes in cat locomotion. Contrary to expectations, this did not destabilize the loop. Indeed, when instability was deliberately evoked by setting displacement feedback gain high, delays in the positive force feedback pathway actually stabilized control. The stabilization of positive force feedback by inherent properties of the neuromuscular system increases the functional scope to be expected of feedback from force receptors in biological motor control. Our results provide a rationale for the delayed excitatory action of Ib heteronymous input on extensor motoneurons in cat locomotion.

Planning an action

The motor control of a sequence of two motor acts forming an action was studied in the present experiment. The two analysed motor acts were reaching-grasping an object (first target) and placing it on a second target of the same shape and size (experiment 1). The aim was to determine whether extrinsic properties of the second target (i.e. target distance) could selectively influence the kinematics of reaching and grasping. Distance, position and size of both targets were randomly varied across the experimental session. The kinematics of the initial phase of the first motor act, that is, velocity of reaching and hand shaping of grasping, were influenced by distance of the second target. No kinematic difference was found between movements executed with and without visual control of both hand and targets. These results could be due to computation of the general program of an action that takes into account extrinsic properties of the final target. Conversely, they could depend on a visual interference effect produced by the near second target on the control of the first motor act. In order to dissociate the effects due to second target distance from those due to visual interference, two control experiments were carried out. In the first control experiment (experiment 2) subjects executed movements directed towards spatial locations at different distances from the first target, as in experiment 1. However, the near second target was not presented and subjects were required to place the object on an arbitrary near position. Distance of the second (either real or arbitrary) target affected the reaching component of the first motor act, as in experiment 1, but not the grasp component. In the second control experiment (experiment 3), the pure visual interference effect was tested. Subjects were required to reach and grasp the object and to lift it in either presence or absence of a second near stimulus. No effect on the initial phase of the first motor act was observed. The results of the this study suggest a dissociation in the control of reaching and grasping, concerning not only visual analysis of extrinsic properties of the immediate target but also visual analysis of the final target of the action. In other words, the notion of modularity for the motor control can be extended to the construction of an entire action.

Weak short-latency spinal projections to the long flexor of the human thumb

The human thumb is controlled by a muscle, flexor pollicis longus (FPL), that is unique among mammals and contributes to manual dexterity. The present study sought to define whether the spinal reflex circuitry for this muscle differed from that for an adjacent muscle (flexor carpi radialis, FCR). In peri-stimulus time histograms, short-latency, largely monosynaptic excitation produced by median nerve stimulation was significantly less frequent and significantly smaller for FPL motor units than FCR motor units. Thus the motoneurone pools of adjacent muscles differ in their spinal reflex accessibility. The reflex control of FPL may thus be achieved by supraspinal pathways rather than the traditional monosynaptic arc.

Proprioceptive control of wrist movements in Parkinson's disease. Reduced muscle vibration-induced errors

The effects upon the trajectories of practised slow (approximately 9 degrees/s) voluntary wrist-extension movements of applying vibration to the tendon of an antagonist muscle (flexor carpi radialis) during the course of the movement have been studied in patients with idiopathic Parkinson's disease and age-matched healthy individuals. In both patient and control groups, flexor vibration elicited undershooting of wrist-extension movements. Wrist extensor and flexor surface EMG recordings indicated that, in patients and controls, such undershooting resulted principally from sustained reductions in extensor (prime mover) activity. Small vibration reflexes were commonly elicited in the wrist flexors which, in both Parkinson's disease and healthy subjects, were usually otherwise virtually quiescent during these slow extension movements. The amplitudes of such vibration reflexes did not differ systematically between patient and control groups and appeared inadequate to have exerted an appreciable braking action upon the extension trajectories. However, the extent of vibration-induced undershooting was, on average, significantly less in the Parkinson's disease group. In a subgroup of patients with asymmetrical parkinsonism the effects of antagonist vibration upon wrist movements of the more and less affected limb were compared. The degree of vibration-induced undershooting was significantly smaller on the more affected side. This finding suggests that disturbed proprioceptive guidance of voluntary movements in Parkinson's disease is related to the severity of clinical motor deficits. A small number Parkinson's disease patients were studied 'ON' and 'OFF' their routine anti-parkinsonian medication. A non-significant tendency was found for vibration-induced errors to be less marked in the 'OFF' state. In a separate series of experiments, under isometric conditions, vibration-induced EMG changes were recorded whilst subjects attempted to maintain a steady (15% maximum) voluntary wrist extensor effort. Results in control subjects suggested that prolonged flexor vibration produced significant tonic reflex reciprocal inhibition of the extensor muscles. However, the strength of reflex inhibition appeared sufficient to account for only a small fraction of the undershooting observed during the movement tasks. Thus, our results are consistent with the existence of an abnormality of higher-level proprioceptive integration in Parkinson's disease in which there is a mismatch of sensory (proprioceptive) and motor (corollary discharge) information.

Mechanoreceptors in the palmar wrist ligaments

Three palmar wrist ligaments from fresh human cadavers were dissected from the proximal to the distal insertions and stained to identify the mechanoreceptors. Golgi organs, Pacinian corpuscles, Ruffini endings and free nerve endings were present in all three ligaments. In the radial collateral and radiolunate ligaments they were found in increased density towards the proximal and distal insertions. A more uniform distribution was found in the radioscaphocapitate ligament which has attachments to three bones. The palmar wrist ligaments may have a significant sensory role in maintaining the stability of the wrist and in controlling its movement. Although technically difficult, the surgical repair of traumatic wrist defects should attempt to preserve the innervation of the ligaments, shown to be mainly near bony attachments. This may allow improvement in postoperative outcomes by preserving some proprioception. In some painful post-traumatic or degenerative conditions, however, denervation may be advantageous.

Effects on muscle activity from microstimuli applied to somatosensory and motor cortex during voluntary movement in the monkey

It is well known that electrical stimulation of primary somatosensory cortex (SI) evokes movements that resemble those evoked from primary motor cortex. These findings have led to the concept that SI may possess motor capabilities paralleling those of motor cortex and speculation that SI could function as a robust relay mediating motor responses from central and peripheral inputs. The purpose of this study was to rigorously examine the motor output capabilities of SI areas with the use of the techniques of spike- and stimulus-triggered averaging of electromyographic (EMG) activity in awake monkeys. Unit recordings were obtained from primary motor cortex and SI areas 3a, 3b, 1, and 2 in three rhesus monkeys. Spike-triggered averaging was used to assess the output linkage between individual cells and motoneurons of the recorded muscles. Cells in motor cortex producing postspike facilitation (PSpF) in spike-triggered averages of rectified EMG activity were designated corticomotoneuronal (CM) cells. Motor output efficacy was also assessed by applying stimuli through the microelectrode and computing stimulus-triggered averages of rectified EMG activity. One hundred seventy-one sites in motor cortex and 68 sites in SI were characterized functionally and tested for motor output effects on muscle activity. The incidence, character, and magnitude of motor output effects from SI areas were in sharp contrast to effects from CM cell sites in primary motor cortex. Of 68 SI cells tested with spike-triggered averaging, only one area 3a cell produced significant PSpF in spike-triggered averages of EMG activity. In comparison, 20 of 171 (12%) motor cortex cells tested produced significant postspike effects. Single-pulse intracortical microstimulation produced effects at all CM cell sites in motor cortex but at only 14% of SI sites. The large fraction of SI effects that was inhibitory represented yet another marked difference between CM cell sites in motor cortex and SI sites (25% vs 93%). The fact that motor output effects from SI were frequently absent or very weak and predominantly inhibitory emphasizes the differing motor capabilities of SI compared with primary motor cortex.

Distal posterior interosseous nerve syndrome

Five patients presenting with chronic dorsal wrist pain and diagnosed as distal posterior interosseous nerve syndrome are reported. Clinical examination revealed point tenderness of the fourth extensor compartment. The symptoms were reproduced by extreme wrist extension in all patients and by extreme flexion in three of the patients. The pain was relieved in all patients by a selective lidocaine block of the terminal branch of the posterior interosseous nerve at the wrist joint. All the patients failed to respond to nonoperative treatment and underwent surgical exploration of the nerve. The operative findings were an enlarged nerve in three patients and adhesion of the nerve to the joint capsule in five patients. A 2 cm section of the nerve proximal to the extensor retinaculum was resected. Four of the five patients had excellent pain relief and returned to full asymptomatic activity. One patient had improvement in pain and was satisfied with the outcome. A diagnosis of distal posterior interosseous nerve syndrome should be considered if the usual sources of dorsal wrist pain are eliminated.

Influence of peripheral nerve stimulation on human motor cortical excitability in patients with ventrolateral thalamic lesion

OBJECTIVE

To determine the peripheral afferent pathways that influence the activities of the motor cortex by examining the effects of peripheral nerve stimulation on motor cortical excitability.

PATIENTS AND METHODS

We examined 12 healthy volunteers and 4 patients with localized brain lesions caused by cerebrovascular attack. Of the 4 patients, 1 patient had pontine infarction, including medial lemniscus, and severe sensory deficit and 3 had small localized lesions in the lateral part of the thalamus and neither sensory impairment nor abnormal N20 waves on somatosensory evoked potential recordings. Central motor tract excitability was examined by measuring a change in the motor evoked potential (MEP), using transcranial magnetic stimulation of the motor cortex after peripheral nerve stimulation at the wrist significantly increased MEP response in the controls at long conditioning-test intervals of 28 to 60 milliseconds, as well as at short intervals of 0 to 6 milliseconds. A late MEP potentiation was not observed on the affected side in all patients.

CONCLUSIONS

The loss of late MEP potentiation in patients with pontine and thalamic lesions indicates that this potentiation is caused by the alternation of the motor cortical excitability. Furthermore, the results in the patients with thalamic lesions suggest that the lateral nuclei of the thalamus, other than the ventral posterolateral nucleus and probably including the ventrolateral nucleus, have an important function in the processing of peripheral sensory input for tuning motor cortical excitability.