Coordination of thumb joints during opposition

Thumb opposition plays a vital role in hand function. Kinematically, thumb opposition results from composite movements from multiple joints moving in multiple directions. The purpose of this study was to examine the coordination of thumb joints during opposition tasks. A total of 15 female subjects with asymptomatic hands were studied. Three-dimensional angular kinematics of the carpometacarpal (CMC), metacarpophalangeal (MCP) and interphalangeal (IP) joints were obtained by a marker-based motion analysis system. Thumb opposition revealed coordination among joints in a specific direction (inter-joint coordination) and among different directions within a joint (intra-joint coordination). In particular, linear couplings existed between the flexion and pronation at the CMC joint, and between the flexion of the CMC joint and flexion of the MCP joint. Principal component analysis showed that only two principal components adequately represented the thumb opposition data of seven movement directions. A term functional degrees of freedom by virtue of principal component analysis was proposed to uncover the extent of movement coordination in functional tasks.     

Arteriovenous malformation of a persistent median artery with a bifurcated median nerve

A patient with arteriovenous malformations of the volar forearm and hand arising from a persistent median artery with an associated bifid median nerve is presented. Surgeons should be aware of high median nerve bifurcations, particularly when a persistent median artery is identified, and should remember that additional structures that can lead to nerve compression may be present in the carpal tunnel. Specifically, more than one median nerve may need to be identified and protected in such cases.     

Modification of median nerve somatic evoked potentials by prior median nerve,peroneal nerve,and auditory stimulation

In a recovery function design, changes were measured in the somatic evoked potentials (SEP) to right median nerve (RMN) shocks preceded by stimulation of: the same nerve (RMN-RMN); the left median nerve having primary input to the homologous sensory area in the contralateral hemisphere (LMN-RMN); the right peroneal nerve having primary input to a different region of the same hemisphere (RPN-RMN); and the auditory nerve with primary input to a different sensory modality (AUD-RMN). Eight inter-stimulus intervals ranged from zero (simultaneous) to 2.5 sec. It was assumed that the degree of interaction between evoked potentials would be related to the degree to which common neural structures are activated or modulated in response to the stimuli. Results were: (a) the primary somatosensory response N20-P30 was little influenced by other somatic or auditory stimulation, interaction occurring predominantly in the RMN-RMN condition; (b) with increasing latency, components showed increasing interaction across modalities; (c) preceding homolateral stimulation (RPN-RMN) showed no greater interaction than preceding contralateral stimulation (LMN-RMN); (d) N55-P100 differed from the primary somatosensory response N20-P30 by showing greater interaction with other somatic stimuli; and (e) N140-P190 showed similarly shaped recovery functions across stimulus pairs but significant differences in magnitude of interaction. These results show that components with similar wave form and topographical characteristics can have different neurophysiological properties.     

Intraneural perineurioma involving the median nerve

Intraneural perineurioma is a rare clinical entity, which tends to affect major nerve trunks in the upper extremities. On light microscopy, numerous pseudo-onion-bulb structures having a central clear area are surrounded by concentric layers of eosinophilic elongate cells having spindled nuclei. Immunohistochemistry of concentric cells stains positive for epithelial membrane antigen but negative for S100 protein. Because of the small number of cases, no consensus has been made on proper treatment of this entity. Although none of the patients who have had excision of tumor with nerve grafting have had sensory nerve recovery, we believe each patient should be individualized until more data are available regarding this tumor.     

Cortical plasticity in patients with median nerve lesions studied with MEG

We have previously shown age- and time-dependent effects on brain activity in the primary somatosensory cortex (SI), in a functional magnetic resonance imaging (fMRI) study of patients with median nerve injury. Whereas fMRI measures the hemodynamic changes in response to increased neural activity, magnetoencephalography (MEG) offers a more concise way of examining the evoked response, with superior temporal resolution. We therefore wanted to combine these imaging techniques to gain additional knowledge of the plasticity processes in response to median nerve injury. Nine patients with median nerve trauma at the wrist were examined with MEG. The N1 and P1 responses at stimulation of the injured median nerve at the wrist were lower in amplitude compared to the healthy side (p?larger N1 amplitude (p?p?p?increased MEG response amplitude to ulnar nerve stimulation. This can be interpreted as a sign of brain plasticity.     

Mentalis muscle responses to median nerve stimulation

Electrical stimulation may produce excitation or inhibition of the motor neurons, as represented the blink reflex and masseter silent period in response to trigeminal nerve stimulation. Clinically, a light touch on the palm may evoke a mentalis muscle response (MMR), i.e. a palmomental reflex. In this study, we attempted to characterize the MMR to median nerve stimulation. Electrical stimulation was applied at the median nerve with recordings at the mentalis muscles. An inhibition study was done with continuous stimuli during muscle contraction (I1 and I2 of MMRaverage). Excitation was done with a single shot during muscle relaxation (MMRsingle) or by continuous stimuli during muscle contraction (E1 and E2 of MMRaverage). The characteristic differences between MMRaverage and MMRsingle were as follows: earlier onset latencies of MMRaverage (MMRaverage < 45 ms; MMRsingle > 60 ms), and a lower amplitude of MMRaverage (MMRaverage < 50 microV; MMRsingle > 150 microV). The receptive field of MMRsingle was widespread over the body surface and that of MMRaverage was limited to the trigeminal, median and index digital nerves. Series of stimuli usually significantly decreased the amplitude of MMRsingle, as a phenomenon of habituation. On the other hand, it was difficult to evoke the earlier response (i.e. MMRaverage) without continuous stimuli and an average technique. MMRaverage had the components of both excitation (E) and inhibition (I); for example, E1-I1-E2-I2 or I1-E2-I2. E2 was the most consistent component. In patients with dorsal column dysfunction, median nerve stimulation could successfully elicit MMRsingle, but not MMRaverage. Contrarily, in patients with pain sensory loss, it was more difficult to reproduce MMRsingle than MMRaverage. It seemed that MMRaverage and MMRsingle did not have equivalents across the different modalities of stimulation.     

Stationary potentials after median nerve stimulation: changes with arm position

We previously reported the presence of stationary negative potentials (N3, N6, N9) over the arm ipsilateral to the side of median nerve stimulation. In this study, we examined the effect of different arm positions upon these stationary peaks in 12 normal subjects. When arm position was changed from elbow extended to elbow flexed 90°, we recorded a new negative peak, N4. The peak latency of N4 corresponded to the traveling impulse reaching the distal biceps brachii. With the elbow flexed, N3, N6 and N9 peak latencies significantly shortened compared to those recorded with the arm in the usual elbow extended position. In contrast, with the arm abducted at the shoulder, N6 and N9 latencies were significantly prolonged while N3 remained unchanged. Corresponding latency shifts were also observed in the bipolarly recorded traveling impulse.We consider 2 possible factors for N4 enhancement by elbow flexion. One is the change in conducting volume surrounding the nerve, i.e., increased muscle bulk of biceps brachii. The other is the change in axial orientation of the propagating nerve impulse by 90°. We also propose that the latency shifts of the stationary potential as well as of a travelling wave can be attributed primarily to relaxation or stretching of the nerve trunk with change in arm position.     

Lipofibromatous hamartoma of the median nerve and macrodactyly

A case of lipofibromatous hamartoma of the median nerve with macrodactyly of 2 digits is described. Nerve stripping resulted in a growth control.     

Lower median nerve block impairs precision grip.

The purpose of this study was to investigate precision grip impairment caused by a lower median nerve block at the wrist. The median nerve block was achieved by injecting bupivacaine hydrochloride into the carpal tunnel, which acutely simulated a median neuropathy. Seven healthy male subjects were instructed to grip, lift, and hold an instrumented handle within 60s using precision grip. The same tasks were performed before and after the nerve block. Force and torque data were recorded using two miniature 6-component force/torque transducers. The precision grip was quantified by the safety margin (i.e. the difference between the actual grip force and the minimal grip force to keep the object from dropping), the variation of grip force, and the migration area of center of pressure (i.e. the area defined by the center of pressure at a digit-transducer surface while holding the handle). Two subjects were unable to complete the precision grip tasks after the nerve block, and their data were excluded from the analyses. The median nerve block caused significant increases (P<0.05) in the safety margin of the grip force (>50%), the grip force variation (>80%), and the area of center of pressure migration (>250%). Median nerve block at the wrist impairs the fine motor control during precision grip. Our results corroborate the important role played by sensory function in hand fine motor control. Clinically, the measures related to precision grip have the potential to quantify impairment of hand function caused by neuromuscular disorders, to monitor the progress of a hand disorder, and to evaluate the efficacy of a treatment or rehabilitation procedure.