The effects of hypertonic dextrose injection on connective tissue and nerve conduction through the rabbit carpal tunnel.

OBJECTIVE: To investigate the effects of hypertonic dextrose injection on the subsynovial connective tissue (SSCT) in a rabbit model. We hypothesized that dextrose injection would induce proliferation of the SSCT, hinder median nerve conduction, and alter SSCT mechanical properties, similar to what is observed in patients with carpal tunnel syndrome (CTS). DESIGN: Randomized, controlled prospective study. SETTING: Not applicable. PARTICIPANTS: New Zealand white rabbits (N=28) weighing 4.0 to 4.5kg. INTERVENTION: One forepaw was randomly injected with 0.1mL 10% dextrose solution. The contralateral paw was injected with a similar amount of 0.9% saline solution as a control. Animals were killed at 12 weeks after injection. MAIN OUTCOME MEASURES: Animals were evaluated by electrophysiology (EP), mechanical testing, and histology. EP was evaluated by distal motor latency and amplitude. Shear force was evaluated when the middle digit flexor digitorum superficialis tendon was pulled out from the carpal tunnel. The ultimate tensile load and the energy absorption were also measured. Tissue for histology was evaluated qualitatively. RESULTS: EP demonstrated significant prolongation of distal motor latency. The energy absorption and stiffness were also significantly increased in the dextrose group. Histologically, the dextrose group showed thickening of the collagen bundles and vascular proliferation within the SSCT compared with the saline group. CONCLUSIONS: These results are consistent with the findings in patients with CTS and suggest that hypertonic dextrose injection has the potential to create a novel animal model in which to study the evolution of CTS.

Anatomical features of the carpal flexor retinaculum of the horse.

This study aims to elucidate the topographical anatomy of the carpal flexor retinaculum or palmar anular carpal ligament (PACL) in the horse. Ten specimen of the carpus of five healthy horses were studied by dissection in layers. Slices of 5 mm in thickness facilitated observation of the soft tissues. The superficial layer of the PACL subdivides into five compartments: one for the palmar nerve and the arterial and venous branches, one for only the radial artery, one for the radial vein, and one for the tendon of the radial carpal flexor muscle, and finally for the deep layer that supports all tendinous structures located palmar to the carpus, as well as the median artery and palmar medial nerve. The sections of the segmented PACL that are affected by carpal canal syndrome may vary with the aetiology of the space-occupying process. Precise anatomical knowledge of the structures may help in understanding the pathological processes and determining the most appropriate therapy.

Characteristics of sensory DRG neurons innervating the wrist joint in rats.

BACKGROUND: Wrist pain can be the result of trauma, or inflammatory processes such as arthritis or synovitis. There is evidence that sensory nerve fibers are present in the wrist joints of animals and humans; however, the sensory innervation pattern of the wrist, as well as the types of nerves innervating it, have not been clarified. The purpose of this study was to characterize the types of sensory dorsal root ganglion (DRG) neurons innervating the wrist joint in the rat. METHODS: In this study, retrograde neurotransport was combined with lectin affinity histochemistry and immunohistochemistry to characterize DRG neurons innervating the wrist joint in rats. We used 3 markers: calcitonin gene-related peptide (CGRP) as a marker of small, peptide-containing neurons associated with inflammatory pain; the glycoprotein binding the isolectin from Griffonia simplicifolia (IB4) for small, non-peptide-containing neurons related to transmission of pain following nerve injury; and neurofilament 200 (NF200) for small and large myelinated fibers. IB4-binding and CGRP-containing neurons are typically involved in pain sensation, whereas NF200 is associated with pain and proprioception. RESULTS: Neurons innervating the wrist joints, retrogradely labeled with fluoro-gold (FG), were distributed throughout DRGs from C6 to T1. Of all of the FG labeled neurons, the percentage of NF200 immunoreactive (IR) neurons and CGRP-IR neurons were 26% and 45%, respectively. The percentage of IB4-binding neurons was 3%, significantly less than the ratio of CGRP-IR neurons to the total FG labeled neurons. CONCLUSION: Under physiological conditions in rats, DRG neurons transmit several types of sensation from the wrist joint including proprioception and pain. Most of the labeled neurons were CGRP-IR peptide containing neurons. It is likely that these neurons are the predominant afferents for inflammatory pain signals from the wrist. Because peptide-containing neurons are associated with inflammatory pain, it is likely that the inflammation in the wrist joint causes wrist joint pain.

Carpal hyperflexion in a growing dog following neural injury to the distal brachium.

A three-month-old dobermann was presented with hyperfiexion of the right carpus. The abnormality had evolved over a three-week period, following circumferential soft tissue trauma to the distal brachium. The carpal joint angle measured at the limit of passive extension was 105 degrees compared with 175 degrees for the left carpus, and prevented placement of metacarpal and digital pads on the ground. Neurological examination revealed marked atrophy of the carpal extensors, an absent extensor carpi radialis reflex and moderate atrophy of the carpal flexors. Spontaneous electromyographic activity consistent with denervation was recorded in the carpal extensor and flexor muscles. Surgical exploration of the distal radial nerve disclosed a region of fibrosis enmeshing the deep branch of the radial nerve. Following relief of the entrapped nerve, carpal hyperflexion, muscle atrophy and the extensor carpi radialis reflex deficit gradually resolved over four months. It is suggested that, In the rapidly growing limb, myoneural dysfunction Induced by trauma was the underlying pathophysiological mechanism for carpal hyperflexion.

Transmission security for single kinesthetic afferent fibers of joint origin and their target cuneate neurons in the cat.

Transmission between single identified, kinesthetic afferent fibers of joint origin and their central target neurons of the cuneate nucleus was examined in anesthetized cats by means of paired electrophysiological recording. Fifty-three wrist joint afferent-cuneate neuron pairs were isolated in which the single joint afferent fiber exerted suprathreshold excitatory actions on the target cuneate neuron. For each pair, the minimum kinesthetic input, a single spike, was sufficient to generate cuneate spike output, often amplified as a pair or burst of spikes, particularly at input rates up to 50-100 impulses per second. The high security was confirmed quantitatively by construction of stimulus-response relationships and calculation of transmission security measures in response to both static and dynamic vibrokinesthetic disturbances applied to the joint capsule. Graded stimulus-response relationships demonstrated that the output for this synaptic connection between single joint afferents and cuneate neurons could provide a sensitive indicator of the strength of joint capsule stimuli. The transmission security measures, calculated as the proportion of joint afferent spikes that generated cuneate spike output, were high (>85-90%) even at afferent fiber discharge rates up to 100-200 impulses per second. Furthermore, tight phase locking in the cuneate responses to vibratory stimulation of the joint capsule demonstrated that the synaptic linkage preserved, with a high level of fidelity, the temporal information about dynamic kinesthetic perturbations that affected the joint. The present study establishes that single kinesthetic afferents of joint origin display a capacity similar to that of tactile afferent fibers for exerting potent synaptic actions on central target neurons of the major ascending kinesthetic sensory pathway.

Postural responses of forelimb extensors to somatosensory signals elicited during wrist rotation: interaction with vestibular reflexes.

The responses of the forelimb extensor triceps brachii (TB) to sinusoidal wrist rotation, at 0.156 Hz, +/-5 degrees, were investigated in decerebrate cats. In most of the tested muscles [12/15) the multiunit electromyographic (EMG) activity of the TB muscle increased during dorsiflexion and decreased during plantar flexion of the ipsilateral limb extremity, showing an average (+/-SD) gain of 1.38+/-0.64 impulses/s/ degrees and a phase lead of 33+/-19 degrees with respect to the extreme dorsiflexion of the forepaw. Both parameters remained unmodified by increasing the amplitude of stimulation from 5 degrees up to 10 degrees. Rotation of the contralateral wrist had no effect on TB activity. When the rotation of the ipsilateral wrist occurred during sinusoidal roll tilt of the whole animal, a stimulus that activates vestibular receptors, the TB response to combined stimulation closely corresponded to the vectorial sum of the individual responses. Dorsiflexion of the forepaw could drive the vestibulospinal system, which excites the ipsilateral TB motoneurons. In fact, functional inactivation of the cerebellar anterior vermis, which controls vestibulospinal neurons, significantly modified the TB response to wrist rotation. It appears, therefore, that the somatosensory signals elicited by wrist rotation utilize the spinocerebellum to modulate the activity of the TB. The TB responses to wrist rotation could play a role in stabilizing posture during stance and locomotion.

Reflex pathways from large muscle spindle afferents and recurrent axon collaterals to motoneurones of wrist and digit muscles: a comparison in cats, monkeys and humans.

Whereas a large body of data is available on the control of hand motoneurones from the brain, not much is known about the contribution of the spinal interneuronal apparatus to the differentiated movement repertoire of the hand. This review summarises recent data on the excitatory Ia pathways and on recurrent inhibition for cats, monkeys and humans. The basic principles of organisation have, in general, been preserved in the different species. Thus the motoneurones to cat and human long and short digit muscles seem not to possess a recurrent axon collateral system. With regard to the Ia pathways, specialised connectivity patterns have developed in the long digit extensor and wrist extensor muscles. They allow the former group to support the differentiated movement repertoire of the digits, and the latter group to be part of a general extensor or flexor synergism. Modifications between the species are present, however, with regard to the proximodistal connectivity across the elbow. Whereas they are regularly present in the cat, they are less developed in the monkey and absent in man, which frees the human hand from the elbow position.