Surgical treatment and outcomes in 15 patients with anterior interosseous nerve entrapments and injuries

Object

The authors present data obtained in 15 surgically treated patients with anterior interosseous nerve (AIN) entrapments and injuries.

Methods

Fifteen patients with AIN entrapments and injuries underwent surgery between 1967 and 1997 at Louisiana State University Health Sciences Center (LSUHSC) or Stanford University Medical Center. Patient charts were reviewed retrospectively. The LSUHSC grading system was used to evaluate the function of muscles supplied by the AIN.

Nontraumatic injuries included seven AIN compressions by bone or soft tissue. Traumatic injury mechanisms consisted of stretch or contusion (six patients), injection (one patient), and burn scar (one patient). Presentations included weakness in the flexor digitorum profundus (FDP) muscle to the index finger, FDP muscle to the middle finger, pronator quadratus muscle, and flexion of the distal phalanx of the thumb. Preoperative evaluations included electromyography and nerve conduction studies as well as elbow and forearm plain radiographs.

On surgery, lesions in continuity involved seven compressions, four stretch or contusion injuries, and one injection injury, all of which demonstrated nerve action potentials (NAPs) and were treated with neurolysis. Among the seven compression and four stretch or contusion injury cases, six and three patients, respectively, had LSUHSC Grade 3 or better functional recoveries postoperatively. Two stretch or contusion injuries involved lesions in continuity but demonstrated negative NAPs at surgery. Thus, each was treated using a graft repair after resection of a neuroma. There was one burn scar injury, which was treated via an end-to-end suture anastomosis, leading to a functional recovery better than Grade 3.

Conclusions

Fifteen AIN entrapments or injuries responded favorably to nerve release and/or repair.

Surgical treatment and outcomes in 45 cases of posterior interosseous nerve entrapments and injuries

Object

The authors report data in 45 surgically treated posterior interosseous nerve (PIN) entrapments or injuries.

Methods

Forty-five PIN entrapments or injuries were managed surgically between 1967 and 2004 at Louisiana State University Health Sciences Center (LSUHSC) or Stanford University Medical Center. Patient charts were reviewed retrospectively. The LSUHSC grading system was used to assess PIN-innervated muscle function.

Injuries were caused by nontraumatic (21 PIN entrapments and four tumors) and traumatic (nine lacerations, eight fractures, and three contusions) mechanisms. Presentations included weakness in the extensor carpi ulnaris muscle, causing compromised wrist extension and radial drift; extensor digitorum, indicis, and digiti minimi muscles with paretic finger extension; extensor pollicis brevis and longus muscles with weak thumb extension; and abductor pollicis longus muscle with rare decreased thumb abduction due to substitutions of the median nerve–innervated abductor pollicis brevis muscle and, at 90°, the extensor pollicis brevis and longus muscles. Preoperative evaluations consisted of electromyography and nerve conduction studies, elbow and forearm plain x-ray films, and magnetic resonance imaging for tumor detection.

At surgery, in continuity lesions were found in 21 entrapments and three fracture-related and three contusion injuries; all transmitted nerve action potentials (NAPs) and were treated with neurolysis. Five fracture-related PIN injuries, one of which was a lacerating injury, were in continuity and transmitted no NAPs; graft repairs were performed in all of these cases. Among nine lacerations, three PINs appeared in continuity, although intraoperative NAPs were absent. Two of these nerves were treated with secondary end-to-end suture anastomosis repair and one with secondary graft repair. There were six transected lacerations: three were treated with primary suture anastomosis repair, two with secondary suture anastomosis, and one with graft repair. Four tumors involving the PIN were resected. Most muscles innervated by 45 PINs had LSUHSC Grade 3 or better functional outcomes.

Conclusions

Forty-five PIN entrapments or injuries responded well to PIN release and/or repair.

Quantitation of and landmarks for the muscular branches of the ulnar nerve to the forearm for application in peripheral nerve neurotization procedures

Object

In neurotization procedures, donor nerves—either whole or in part—with relatively pure motor function can be carefully chosen to provide the optimal nearby motor input with as little donor site morbidity as possible. In this context, the ulnar nerve branches to the forearm muscles are relatively dispensable; however, quantitation of and landmarks for these branches are lacking in the literature.

Methods

The ulnar branches to the flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP) muscles in 20 upper extremities obtained in adult cadaveric specimens were dissected and quantified.

In the forearm, a mean of four nerve branches led to the FCU and FDP muscles. A mean of 3.4 branches led to the FCU muscle; of these, one to three were medial branches and zero to two were lateral. Medial branches to the FCU muscle originated a mean of 2.7 cm inferior to the medial epicondyle. Lateral branches to the FCU muscle originated at a mean of 3.3 cm inferior to the medial epicondyle. The mean length of the medial branches was 3.2 cm, whereas the mean length of the lateral branches was 3.3 cm. All nerves had a single trunk for the FDP muscle, and in all specimens this branch was located deep to the main ulnar nerve trunk, originating from the ulnar nerve a mean of 2.7 cm inferior to the medial epicondyle. These branches had a mean length of 5.6 cm. The mean diameter of all medial and lateral branches to the FCU muscle was 1 mm, and the mean diameter of the branch to the FDP muscle was 2.1 mm. All branches to both the FCU and FDP muscles arose from the ulnar nerve, over its first approximately 5 cm from the level of the medial epicondyle. Additionally, all branches could be easily lengthened by gentle proximal dissection from the main ulnar nerve.

Conclusions

Ulnar branches to the forearm can be easily localized and used for neurotization procedures. The branch to the FDP muscle had the greatest diameter and longest length, easily reaching the median nerve and posterior interosseous nerve via a transinterosseous membrane tunneling procedure. Furthermore, this branch could be teased away from the main ulnar nerve trunk and made to reach the distal branches of the musculocutaneous nerve in the arm.

Augmentation of the contraction force of human thenar muscles by and during brief discharge trains

We investigated the influence of the history of activity on the contractile properties of abductor pollicis brevis (APB) to define how the forces produced by individual stimuli change within a stimulus train, with a view to clarifying the optimal discharge frequency for force production in brief trains. Supramaximal electrical stimuli were delivered to the median nerve at the wrist singly or in trains of 2-5 at various interstimulus intervals (ISIs). The force and electromyographic (EMG) responses to trains of n stimuli were defined by online subtraction of the responses to n - 1 stimuli. The force attributable to the nth stimulus was normalized to that produced by a single stimulus. The contraction force produced by 2 stimuli exceeded the force expected with linear summation of 2 single twitches by 30-40% at ISIs of 2-100 ms. Increasing the number of stimuli resulted in less augmentation of the force produced by the last stimulus in the train for ISIs up to 20 ms, but greater augmentation for ISIs of 50-100 ms. At ISIs of less than 10 ms, the time to peak force produced by the last stimulus in a 5-pulse train was delayed by approximately 100 ms, the peak force produced by that stimulus was less than that produced by a single stimulus, and it occurred on the falling phase of the overall contraction. These properties are best explained by the catchlike property of muscle. This implies that the augmentation of contraction force due to this property can increase throughout a stimulus train, and is not restricted to the doublet discharges that have conventionally been studied. We conclude that, with brief discharge trains, maximal forces occur at ISIs of 56-75 ms, intervals that are longer than those conventionally associated with the catchlike property. Discharge rates of 15-20 HZ appear to be optimal for force generation by APB during steady contractions.

Latent addition in human motor and sensory axons: Different site-dependent changes across the carpal tunnel related to persistent Na+ currents

OBJECTIVE

To compare site-dependent changes across the carpal tunnel in axonal persistent Na+ conductances in motor and sensory axons. Positive sensory symptoms are prominent features in carpal tunnel syndrome, and a persistent Na+ current is a major determinant of axonal excitability.

METHODS

The technique of latent addition was used to estimate persistent Na+ currents in median motor and sensory axons at the wrist and palm of 10 normal subjects. Brief hyperpolarizing conditioning current pulses were delivered, and threshold change at the conditioning-test interval of 0.2 ms was measured as an indicator of persistent Na+ currents.

RESULTS

Threshold changes at 0.2 ms were greater in sensory than in motor axons at both the wrist and palm. In motor axons, the threshold changes were significantly smaller at the palm (mean, 4.9%) than at the wrist (10.0%). By contrast, the threshold changes were similar at the two sites of sensory axons (12.6 and 13.1%). The passive membrane time constant was similar for motor and sensory axons at the palm and wrist.

CONCLUSIONS

Nodal persistent Na+ conductances have substantial site-dependent changes decreasing distally across the carpal tunnel in median motor axons, but not in sensory axons.

SIGNIFICANCE

Whereas sensory axons generally have higher excitability than motor axons, the sensory-motor differences become more prominent across, and possibly at the carpal tunnel than the nerve trunk, and it is suggested that this contributes to the predominance of positive sensory symptoms in carpal tunnel syndrome.

Emotion and movement: Activation of defensive circuitry alters the magnitude of a sustained muscle contraction

Understanding the emotion-movement relationship is crucial to the development of motor theory and movement rehabilitation recommendations for a wide range of diseases and injuries that involve motor impairment. Behaviorally, when movements are executed following exposure to emotional stimuli, evidence suggests that active defensive circuitry results in faster but more variable voluntary movements. However, each of the existing protocols has involved movement execution following the offset of anxiety or emotion eliciting stimuli. The specific aim of this study, therefore, was to determine whether the continued exposure to emotional stimuli would alter the magnitude and variability of a sustained motor contraction. During the presentation of pleasant, unpleasant, neutral, and blank images, participants (N=45) were instructed to respond to the onset of an auditory stimulus by initiating and then sustaining a maximal bimanual isometric contraction of the wrist and finger extensor muscles against two independent load cells (left/right limb). Corroborating previous evidence and supporting hypothesis 1, findings indicated that exposure to unpleasant images lead to an increase in mean force production. Variability of movement, however, did not vary as a function of affective context. These findings indicate that continued exposure to unpleasant stimuli magnifies the force production of a sustained voluntary movement, without sacrificing the variability of that contraction. Mechanism driven open and closed loop explanations are offered for these phenomena, implications are addressed, and future directions are discussed.

Abnormal ulnar nerve anatomy in the distal forearm pre-disposes to post-traumatic ulnar neuritis at the wrist

Anatomical variations of the ulnar nerve have been described at the level of the elbow and in Guyon's canal, while the path in the forearm has always been assumed to be constant. We present a case of compressive ulnar neuropathy at the wrist pre-disposed by a presumed congenital variation of the path of the ulnar nerve at the level of the wrist which improved following surgical release of the constriction caused as a result of it.

Nerve blocks at the wrist for carpal tunnel release revisited: the use of sensory-nerve and motor-nerve stimulation techniques

BACKGROUND AND OBJECTIVES

Because the median nerve at the wrist has mainly sensory endings, the aim of this study was to assess the response of the median nerve to nerve stimulation at the wrist and to evaluate the quality of median nerve block. A control group of patients who received blinded injections was analyzed and compared post hoc.

METHODS

One hundred and eleven patients scheduled for ambulatory endoscopic carpal-tunnel release performed under median and ulnar nerve blocks at the wrist were prospectively studied. The blocks were performed with a nerve stimulator. Nerve-stimulation techniques were explained to the patient before the block was performed. The patient was trained to inform the anesthetist of their perception of an electrical paresthesia that was synchronized to the nerve stimulator. The anesthetist recorded the first response of the patient to nerve stimulation: sensory (S), sensory-motor (SM), or motor response (M). When the minimal stimulating current was obtained, an equal volume of 4 mL of 1.5% mepivacaine was injected on median and ulnar nerves. If necessary, a lateral subcutaneous injection of 2 mL of 1.5% mepivacaine was administered at the wrist crease in the musculocutaneous nerve area. Thirty-five patients who received blinded local anesthetics injections were included post hoc. Quality of anesthesia was compared between groups.

RESULTS

Responses included 89 S (80.2%), 18 SM (16.2%), and 4 M (3.71%). No differences occurred in time to perform the block, minimal current intensity, and efficacy. More punctures were necessary in the M group compared with the S group and the control group (P < .05). The onset time of sensory blocks increased significantly in control-group patients (P < .05), but the duration of the nerve-block procedure decreased in comparison with the M group. Respectively, 10% and 20% of patients experienced mild or severe pain in the nerve-stimulation group and control group. At 20 minutes, the block was complete for the median and ulnar nerves in 96.4% and 85% of the nerve-stimulation patients and control patients (P < .05). Two patients in the control group experienced painful mechanical paresthesia. Neither permanent nor transient nerve injuries were observed during or after the nerve block or surgery.

CONCLUSION

This study describes how infrequently an initial motor response is identified when a nerve stimulator is used on the median nerve at the wrist. A very high success rate of median and ulnar nerve block at the wrist is obtained by use of sensory or sensory-motor-nerve stimulation and less than 10 mL of anesthetic solution.

The contribution of proprioceptive feedback to sensorimotor adaptation

It is known that proprioceptive signals from muscles, joints, and skin are involved in the execution of aimed arm movements, but their role in the acquisition of new motor behaviour is largely unknown. Previous research using deafferented patients yielded inconsistent findings: sensorimotor adaptation was found to be less, equal, or even better than in controls. The present study uses a different approach: we degraded proprioceptive signals in healthy subjects by wrist vibration, while leaving them intact in a control group. In order to induce sensorimotor adaptation, both groups executed pointing movements under a visual (Exp. A) or a mechanical perturbation (Exp. B). We found that adaptation to the visual distortion was little affected by vibration, while adaptation to the mechanical distortion was substantially impaired. We conclude that proprioceptive signals which overtly disagree with visual ones (Exp. A) are not used for adaptation, while those which largely agree with visual ones (Exp. B) are used to enhance adaptive recalibration. These results indicate that intact proprioception is needed for mechanical but not for visual adaptation, which implies that the underlying mechanisms are at least partly distinct.

Induction of plasticity in the dominant and non-dominant motor cortices of humans

There are clear hemispheric differences in the human motor system. Studies using magnetic resonance morphometry have shown that representation of hand muscles is larger in the dominant hemisphere than the non-dominant hemisphere. There is some limited evidence of electrophysiological differences between hemispheres. For example, it has been reported recently that there is less intracortical inhibition in the dominant hemisphere than the non-dominant hemisphere, and it has been hypothesised that this reduction in inhibition may facilitate use-dependent plasticity in the dominant motor cortex. In the present study we examined this hypothesis in human subjects by examining plasticity induction in both dominant and non-dominant hemispheres using an experimental paradigm known to induce motor cortical plasticity, namely paired associative stimulation (PAS). Additionally, we investigated changes in dominant and non-dominant hand performance on a simple ballistic training task. Short-interval intracortical inhibition (SICI) was also measured for both dominant and non-dominant hands at a range of conditioning intensities. There was significantly less SICI in the dominant motor cortical hand area than in the non-dominant hand area. PAS induced a significant, and similar, increase in motor cortical excitability in both the dominant and non-dominant hemispheres. Motor training resulted in significant performance improvement in both dominant and non-dominant hands. However, there was significantly more improvement in the non-dominant hand. The results from these studies provide some further evidence of electrophysiological differences between the motor cortices of the two hemispheres. Additionally, these findings offer no support for the hypothesis that the dominant hemisphere is positioned more favourably, due to decreased inhibitory tone, than the non-dominant hemisphere for use-dependent plasticity.

Postural adjustments and bearing angle use in interceptive actions

The experiment investigates the effect of ball velocity and walking direction on the adherence to the bearing angle (BA) strategy in adults. Adult participants (N=12) approached a moving ball in order to manually intercept it at a predefined target area. Results revealed that during locomotion the BA strategy was implemented, but on reaching the point of interception, this strategy broke down and the BA strategy of the wrist compensated for the movement requirements relative to the ball velocity and approach angle. Larger deviations from the BA occurred when the angle of approach was decreased and when the ball velocity increased. When the BA strategy was adhered to, postural adjustments were reduced. Increased movements occurred in a proximal-distal direction with an increasing approach angle and a faster ball velocity.

Strength deficits in primary focal hand dystonia

Cortical activation is reduced when patients with focal dystonia perform movements that do not induce dystonic posturing. This finding suggests that the cortical drive to muscles may in some circumstances actually be reduced not increased, as suggested by basal ganglia models of dystonia as a hyperkinetic disorder. The purpose of this study was to examine flexor and extensor strength at the wrist (a clinically affected joint) and elbow (a nonclinically affected joint) in 18 patients with primary focal hand dystonia compared to matched control subjects. We measured peak torque from maximum voluntary contractions, and agonist and antagonist muscle activation by means of surface electromyograms. Patients were significantly weaker than controls at both the elbow and wrist joints and in both flexors and extensors compared to controls. Peak elbow flexion torque was, on average, 14.4% lower in the dystonic compared to the control group, elbow extensor peak torque was 28.6% lower, wrist flexor peak torque was 17.4% lower, and wrist extensor peak torque was 20.7% lower. Strength did not differ as a function of clinical severity. Reductions in peak torque were accompanied by reduced agonist activation, although this finding only reached statistical significance at the elbow. The amount of co-contraction of antagonistic muscles was not significantly different between the two groups. These results are discussed in the context of dystonia as a disorder resulting from dysfunction of basal ganglia output.

Neurotization with the brachialis muscle motor nerve

Function of the wrist and hand in lower root avulsions is severely impaired. Based on anatomic and experimental studies which suggest that the motor nerve of the brachialis muscle could be used as a selective neurotizator in lower root avulsions with intact C5-C6 +/- C7 roots (Klumpke paralysis), we considered its use depending on the target. We describe two techniques for the median nerve (in C8-T1 avulsions) and one for the radial nerve (in C7-C8-T1 avulsions). In all cases, we added the lateral cutaneous nerve of the forearm in the neurotization to improve sensibility in the hand. The present report presents the results of its use in our first five patients.

Spatial and kinematic features of apraxic movement depend on the mode of execution

Knowledge about the dependency of apraxic movements on the mode of execution may enhance the understanding of apraxia and of the cerebral representation of actions. We examined a common tool-use action in nine patients with left hemisphere damage and apraxia. Arm movements during the use of a handsaw were measured and tested in three different modes of execution: pantomime, pantomime with a bar shaped like the handle of the saw, and actual sawing. Analysis concentrated on spatial and kinematic features of the wrist trajectories during these repetitive movements. In healthy control subjects, both pantomime conditions differed from actual use mainly by larger amplitudes during miming. Apraxic patients executed large proportions of their pantomiming movements in an incorrect direction away from the appropriate anteroposterior direction, while other movement features were normal. The availability of the handle-like bar did not improve performance. During actual use, movement direction was constraint by mechanical demands. In this condition patients moved with moderately decreased velocity. However, this deficit was not related to the errors in movement direction characteristic of pantomiming. These data suggest that pantomiming and actual execution of an action are dictated by different external requirements and constraints, pantomiming serves to convey information, while actual use has to obey the mechanical demands of the task. Due to these differences, spatial and kinematic movement features in healthy subjects vary between the modes of execution, movements are differently vulnerable to apraxia, and deficits in patients may dissociate.

Longitudinal incision in surgical release of De Quervain disease

The objective of this paper is to contrast the use of a longitudinal incision in surgical decompression of De Quervain disease with a transverse incision. The advantages are ease in recognition of compartment variations and superficial branches of radial nerve and prevention of palmar tendon subluxation by permitting a more dorsal release of the compartment sheath. Since 2002, we have used a longitudinal skin incision instead of the classic transverse incision to release the first dorsal compartment.

Cyclic time course of motor excitability modulation during the observation of a cyclic hand movement

The observation of a sinusoidal flexion-extension of the wrist was utilized to determine the continuous time course and phase relation between observed movement and its effects on the observer's motor pathways. While observing movements performed by others, the observers' cortical motor areas and spinal circuits were activated, reflecting the specific temporal and muscular pattern of the actual movement (motor resonance). H-reflexes and motor-evoked potentials (MEPs) were elicited, respectively, by electrical stimulation of the median nerve and magnetic stimulation of the appropriate cortical area, in the right forearm muscle Flexor Carpi Radialis (FCR) of subjects who were observing a 1-Hz cyclic oscillation of the right prone hand executed by a different person. Observation elicited a parallel cyclic excitability modulation of the observer's H-reflex and MEP responses with identical period as the observed movement. Modulation was phase advanced, as is muscle activation with respect to the real movement. The same results were obtained when the observed hand oscillation was executed with different frequency (1.6 Hz) and when the hands of mover and observer were supine. No motor resonance was elicited by observing the oscillation of a metal platform. The excitability modulation of MEPs simultaneously monitored in both antagonists of the observer's forearm (FCR and Extensor Carpi Radialis, ECR) was in almost perfect phase opposition, reflecting their natural reciprocal activation during the execution of a hand oscillation. These findings suggest that during observation, motor pathways are modulated subliminally reproducing with high temporal fidelity the motor commands needed to execute the observed movement.

Ulnar nerve compression in Guyon's canal in the presence of a tortuous ulnar artery

A case of ulnar nerve compression in Guyon's canal occurring in the presence of a tortuous ulnar artery in the canal is presented and the pathology and classification of ulnar nerve compression in Guyon's canal discussed.

[Efficacy, side effects and patient satisfaction with wrist conduction block anaesthesia prior to the treatment of palmar hyperhidrosis with botulinum toxin type A]

BACKGROUND

The treatment of palmar hyperhidrosis with botulinum toxin type A (BTX A) injections is one of the most effective therapeutic options. However, without adequate anaesthesia this treatment is not feasible in most patients. The anaesthesia of the radial, median and ulnar nerves (wrist block) is despite the absence of good data considered effective but risky.

PATIENTS AND METHODS

Between 1.10.1999 and 30.9.2001 retrospectively the efficacy, side effects and the patient satisfaction regarding the overall performance of the wrist block prior to the treatment of the palmar hyperhidrosis with BTX A was investigated. The study took place at the department of dermatology in Mannheim.

RESULTS

Of the 38 patients treated, 33 were finally included into the trial. The patients chose the average score of 7,9 +/- 2,1 (sd) on a scale from "0" to "10" (not at all effective--maximally effective) for the efficacy of the wrist block in reducing pain. The patients were very content with the wrist block and granted it the average score of 7,7 +/- 2,1 (sd) on a scale from "0" to "10" (not at all content--maximum content). Unwanted effects could be seen in 31/33 patients (93,9%): these were dizziness, headache or haematoma at the spot of injection as well as pain caused by the injections of the local anaesthesia or paresthesias such as tickling of the hand or arm. All side effects caused by the wrist block were reversible and lasted--except in one patient--only for a short time. 29/33 patients (87,9%) recommended the wrist block prior to treating palmar hyperhidrosis with BTX A and 28/33 patients (84,9%) could not imagine to agree to such a treatment without local anaesthesia.

CONCLUSION

The wrist block effectively reduces pain due to the treatment of palmar hyperhidrosis with BTX A. Major side effects are rare; patient acceptance and satisfaction are high.

Wrist denervation and the anterior interosseous nerve: anatomic considerations

PURPOSE

Wrist denervation via resection of the distal anterior interosseous nerve (AIN) and the posterior interosseous nerve (PIN) is an effective treatment for chronic wrist pain. When performing this procedure through a dorsal approach we have been impressed by anatomic variations of the AIN. This has raised concerns about potential denervation of the pronator quadratus (PQ). The purpose of this study was to elucidate the anatomy of the AIN and PIN as encountered through a dorsal distal forearm incision.

METHODS

Ten fresh-frozen cadavers were dissected. Before dissection radiographs were obtained to ensure accurate localization of the proximal ulnar head with a radiopaque marker. A dorsal approach to the distal forearm was made to identify the anatomy of the PIN and AIN. The location and diameter of all AIN branches were noted by using an operating stereoscopic microscope at x 25 magnification and a precision caliper. The PIN anatomy and size also were noted.

RESULTS

The anatomy of the AIN was variable. The average AIN diameter proximal to the PQ was 1.5 mm. The average number of AIN motor branches was 4.2. The largest PQ motor branch was the first motor branch and was located at an average distance of 37.9 mm from the proximal ulnar head. The last motor branch was found an average of 23.9 mm from the proximal ulnar head. In 9 of 10 specimens the sensory branch tunneled radially through the distal PQ and innervated the periosteum of the volar distal radius. In 4 of 10 specimens a separate branch to the distal radioulnar joint was present. We found an average PIN diameter of 0.87 mm.

CONCLUSIONS

Resection of the AIN at a point 4 cm proximal to the proximal point of the ulnar head would denervate completely the PQ in our cadaver population. Division of the AIN 2 cm proximal to the ulnar head would spare most of the PQ motor branches.

Corticomuscular coherence is increased in the small postural tremor of Parkinson's disease

The mechanisms and electrophysiological characteristics of the postural tremor in Parkinson's disease (PD) have not been defined. We hypothesized that PD subjects with small amplitude postural tremor would show increased corticomuscular coherence at certain frequencies compared to PD subjects without visible tremor. Four groups of participants were studied: (1) Control without postural tremor, (2) Control with small amplitude postural tremor, (3) PD without postural tremor, and (4) PD with small amplitude postural tremor. Accelerometry and electroencephalography-electromyography fast-fourier transform and corticomuscular coherence spectra were generated. Findings showed (1) elevated corticomuscular coherence centered at 12-18 Hz in PD with small amplitude postural tremor; (2) 5-12 Hz accelerometer frequency peaks that did not shift with increasing weight loads in some individuals; and (3) 5-8 Hz accelerometer peaks that shifted frequency with increasing weight loads, consistent with a peripheral-mechanical oscillator in all groups. The small amplitude postural tremor in PD arises from heterogeneous oscillator mechanisms. The discovery of increased corticomuscular coupling shows cortical involvement in the small amplitude postural tremor of PD.

Radial nerve excursion and strain at the elbow and wrist associated with upper-extremity motion

PURPOSE

This study evaluated the excursion necessary to accommodate common motions of daily living and associated strain on the radial nerve. The radial nerve was evaluated at the wrist and proximal to the elbow before it bifurcated.

METHODS

Five fresh-frozen transthoracic cadaver specimens (10 arms) were dissected; the radial nerve was exposed at the elbow and wrist only enough to be marked with a microsuture. Excursion was measured using a laser mounted on a caliper fixed to the bone and aligned in the direction of nerve motion. Strain was measured with a device applied to the nerve at the elbow. Nerve excursion associated with motion of the shoulder, elbow, wrist, and fingers (measured by a goniometer) was assessed at the wrist and elbow.

RESULTS

An average of 4.3 mm of radial nerve excursion was required at the wrist to accommodate wrist motion from 15 degrees of radial deviation to 30 degrees of ulnar deviation and 8.8 mm was needed for elbow motion from 10 degrees to 90 degrees . The radial nerve at the elbow experienced a 28% strain associated with the same motion of flexion and extension at the elbow. When all the motions of the wrist, fingers, elbow, and shoulder were combined 9.4 mm of radial nerve excursion was required at the wrist and 14.2 mm at the elbow.

CONCLUSIONS

Any factor that limits excursion at these sites could result in repetitive traction of the nerve and possibly could play a role in the pathophysiology of a mechanical neuropathy, which in the case of the radial nerve most often manifests as pain.

The disynaptic group I inhibition between wrist flexor and extensor muscles revisited in humans

The present studies are designed to further characterise the interneuronal pathway mediating the disynaptic reciprocal group I inhibition between flexors and extensors at the wrist and the elbow levels in humans. In the first series of experiments, we compared the electrical threshold of the reciprocal group I inhibition at the wrist and the elbow level after a prolonged vibration aimed at raising the electrical threshold of the antagonistic activated Ia afferents. Prolonged vibration to the 'conditioning' tendon, which raised significantly the electrical threshold of the inhibition at the elbow level, did not alter it at the wrist level. These results suggest that the dominant input to the relevant interneurones is Ia in origin at the elbow level but Ib in origin at the wrist level. In the second series of experiments, using the spatial facilitation method, we compared the effects on the post-stimulus time histograms of single voluntarily activated motor units of two volleys delivered both separately and together to group I afferents in the nerves supplying the homonymous and antagonistic muscles. At the wrist, but not at the elbow level, the peak of homonymous monosynaptic group I excitation was reduced on combined stimulation, although the antagonistic IPSP was just at the threshold. Because the suppression did not involve the initial bins of the peak, it is argued that the suppression is not due to presynaptic inhibition of Ia terminals, but probably reflects convergence between the homonymous and antagonistic volleys onto the interneurones mediating the disynaptic inhibition. Taken together with the previously reported effects of recurrent inhibition on reciprocal inhibition, these results suggest that inhibition between flexors and extensors is differently organised at the elbow (reciprocal Ia inhibition) and the wrist (non-reciprocal group I inhibition) levels. It is argued that the particular connectivity at the wrist level might correspond to some functional requirements at this ball joint.

Neuronal activity in primary motor cortex differs when monkeys perform somatosensory and visually guided wrist movements

This study was designed to investigate how activity patterns of primary motor cortical (MI) neurons change when monkeys perform the same movements guided by somatosensory and/or visual cues. Two adult male rhesus monkeys were trained to make wrist extensions and flexions after holding a steady position during an instructed delay period lasting 0.5-2.0 s. Monkeys held against a 0.07 Nm load that opposed flexion movements. Wrist movements were guided by vibratory cues (VIB-trials), visual cues (VIS-trials), or both in combination (COM-trials). Extracellular recordings of 188 MI neurons were made during all three paradigms. Individual neurons were counted twice, once for each movement direction, yielding 376 cases. All neurons had significant task-related activity (TRA) changes relative to delay period activity during at least one of the three paradigms. TRA was analyzed to determine if it was different as a function of the sensory cue(s) that initiated movement and that specified movement endpoints. Cases were grouped by whether the TRA changes were greater in VIB- or VIS-trials; this defined their "bias". One hundred and eighteen cases (31.4%) had greater TRA changes in VIB-trials (Vb-neurons), whereas 185 (49.2%) showed greater TRA changes in VIS-trials (Vs-neurons). The remaining 73 cases (19.4%) had similar TRA changes in VIB- and VIS-trials (Nb-neurons). For Vb- and Vs-neurons, earlier TRA onsets and greater TRA changes were observed in the trials for which these neurons were biased. During the COM-trials, the TRA was intermediate. During the trials for which the activity was not biased, the TRA was the least. For Nb-neurons, no significant TRA differences were observed across paradigms. TRA changes of MI neurons may represent movement planning-related inputs from other central, presumably cortical, sources as well as contribute to motor outflow from the cortex. These data suggest that Vb- and Vs-neurons are affected differently by somatosensory- and visually related central inputs, resulting in different TRAs, even for essentially identical movements. Such differences may depend not only on the type of sensory information that initiates movement but also whether that information specifies movement endpoints or might interfere with movement monitoring.

Principal component analysis of complex multijoint coordinative movements

Principal components analysis (PCA) has not been very much in vogue within the field of movement coordination even though it is useful to reduce data dimensionality and to reveal underlying data structures. Traditionally, studies of coordination between two joints have predominantly made use of relative phase analyses. This has resulted in the identification of principal constraints that govern the Central Nervous System's organization and the control of coordination patterns. However, relative phase analyses on pairwise joints have some drawbacks because they are not optimal for revealing convergent patterns among multijoint coordination modes and for unraveling generic control strategies. In this paper, we present a method to analyze multijoint coordination based on the properties of PC, more specifically the eigenvalues and eigenvectors of the covariance matrix. The comparison between relative phase analysis and PCA shows that both provide similar and consistent results, underscoring the latter technique's sensitivity to the study of coordination performance. In addition, it provides a method for automatic pattern detection as well as an index of performance for each joint within the context of the global coordination pattern. Finally, the merit of the PCA technique within the context of central pattern generators (CPG) will be discussed.