Peripheral projections of sensory fascicles in the human superficial radial nerve

Restoration of sensory information via bionic hands

Individuals who have lost the use of their hands because of amputation or spinal cord injury can use prosthetic hands to restore their independence. A dexterous prosthesis requires the acquisition of control signals that drive the movements of the robotic hand, and the transmission of sensory signals to convey information to the user about the consequences of these movements. In this Review, we describe non-invasive and invasive technologies for conveying artificial sensory feedback through bionic hands, and evaluate the technologies' long-term prospects.

Effect of dorsal nerve fascial island flap on repairing distal soft tissue defects at the proximal segment of the index, middle, ring, and little fingers

Background

To investigate the effect of the dorsal nerve fascial island (DNFI) flap on repairing finger soft tissue defects at the distal segments.

Methods

Fifty patients with distal soft tissue defects at the index, middle, ring, or little fingers were treated with a DNFI flap at the proximal phalanx between February 2008 and May 2018. The nutrient vascular chain around the dorsal branch of the proper palmar digital nerves served as the flap axis. The dorsal branch of the proper palmar digital arteries provided blood supply. The fascia pedicle served as the venous system. All patients were followed for 6 months.

Results

All 50 flaps survived. The appearance, color, and texture of the skin returned to normal. The sensory function was partially restored. The two-point discrimination of the finger flap was 7–10 mm.

Conclusions

The DNFI flap at the proximal phalanges of the index, middle, ring, and little fingers is an effective surgical option. The technique has a high flap survival rate and long pedicle, which can repair different parts of the finger. The flap also restores the sensory function of the finger without damaging the main nerves or blood vessels. The flap treatment is an optimal option for finger soft tissue defects at the distal segments.

Anatomical variations of the superficial branch of the radial nerve and the dorsal branch of the ulnar nerve: A detailed electrophysiological study

INTRODUCTION

In this study we evaluated anatomic variations of the superficial branch of the radial nerve (SBRN) and the dorsal branch of the ulnar nerve (DBUN) electrophysiologically.

METHODS

Antidromic nerve conduction studies (NCS) of the SBRN and DBUN were performed on healthy individuals. To identify individual responses from the distal branches of the SBRN and DBUN, sensory nerve action potentials of each finger (lateral side/medial side) were recorded.

RESULTS

NCS were performed in 50 hands of 27 healthy control subjects. The thumb and the index finger were supplied by the SBRN in all cases. The lateral and medial sides of the third finger were supplied by the SBRN in 94.0% and 74.0% of the cases, but the lateral and medial sides of the fourth finger were supplied by the SBRN in only 10.0% and 2.0% of cases. The fifth finger and the medial side of the fourth finger were always supplied by the DBUN. The lateral side of the fourth finger was supplied by the DBUN in 98.0% of cases, but the lateral and medial sides of the third finger were supplied by the DBUN in 40.0% and 70.0% of cases. Dual innervation by the SBRN and DBUN was found in 34.0% and 46.0% of the lateral and medial sides of the third finger, but in only 8.0% and 2.0% of the lateral and medial sides of the fourth finger.

DISCUSSION

There are considerable anatomic variations of the SBRN and DBUN in healthy individuals.

Evidence for sparse C-tactile afferent innervation of glabrous human hand skin

C-tactile (CT) afferents were long-believed to be lacking in humans, but these were subsequently shown to densely innervate the face and arm skin, and to a lesser extent the leg. Their firing frequency to stroking touch at different velocities has been correlated with ratings of tactile pleasantness. CT afferents were thought to be absent in human glabrous skin; however, tactile pleasantness can be perceived across the whole body, including glabrous hand skin. We used microneurography to investigate mechanoreceptive afferents in the glabrous skin of the human hand, during median and radial nerve recordings. We describe CTs found in the glabrous skin, with characteristics comparable with those in hairy arm skin, and detail recordings from three such afferents. CTs were infrequently encountered in the glabrous skin and we estimate that the ratio of recorded CTs relative to myelinated mechanoreceptors (1:80) corresponds to an absolute innervation density of around seven times lower than in hairy skin. This sparse innervation sheds light on discrepancies between psychophysical findings of touch perception on glabrous skin and hairy skin, although the role of these CT afferents in the glabrous skin remains subject to future work.NEW & NOTEWORTHY Human touch is encoded by low-threshold mechanoreceptors, including myelinated Aβ afferents and unmyelinated C-tactile (CT) afferents. CTs are abundant in hairy skin and are thought to code gentle, stroking touch that signals positive affective interactions. CTs have never been described in human glabrous skin, yet we show evidence of their existence on the hand, albeit at a relatively low density. Glabrous skin CTs may provide modulatory reinforcement of gentle tactile interactions during touch using the hands.

Effects of targeted activation of tongue muscles on oropharyngeal patency in the rat

Laboratory rats were acutely implanted with an electrode array composed of eight independently controllable contacts applied to ventral and dorsal aspects of the left and right hypoglossal nerves (HGNs) and their branches. Bipolar intramuscular electromyographic (EMG) electrodes were implanted into the left and right genioglossus, hyoglossus and styloglossus muscles to identify which muscles were activated during stimulation via the contacts. Elicited movements, including changes in the position of the tongue and in the size and the shape of the airway, were documented video-graphically through a surgery microscope and an endoscope. Constant current electrical stimulation activated various combinations of electrode contacts and the stimulation patterns were correlated with corresponding oral movements, airway sizes, and EMG activities. Results demonstrate that graded responses and differential activation of the various tongue muscles are achievable by stimulation of specific contacts in the electrode array. These effects are interpreted to result from the targeted activation of regions of the nerve lying under and between the electrodes. Further testing established that the muscle responses elicited by unilateral electrical stimulation with the present approach can be smoothly graded, that the muscle responses resulted in opening of the airway and could be reliably maintained for long durations.

Small fiber neuropathy: is skin biopsy the holy grail?

Small fiber neuropathy (SFN) is characterized by negative sensory symptoms (thermal and pinprick hypoesthesia) reflecting peripheral deafferentation and positive sensory symptoms and signs (burning pain, allodynia, hyperalgesia), which often dominate the clinical picture. In patients with pure SFN, clinical and neurophysiologic investigation do not show involvement of large myelinated nerve fiber making the diagnosis of SFN challenging in clinical practice. Over the last 15 years, skin biopsy has emerged as a novel tool that readily permits morphometric and qualitative evaluation of somatic and autonomic small nerve fibers. This technique has overcome the limitations of routine neurophysiologic tests to detect the damage of small nerve fibers. The recent availability of normative reference values allowed clinicians to reliably define the diagnosis of SFN in individual patients. This paper reviews usefulness and limitations of skin biopsy and the relationship between degeneration and regeneration of small nerve fibers in patients with diabetes and metabolic syndrome.

Cutaneous nerve transection for the management of intractable upper extremity pain caused by invasive squamous cell carcinoma

A recurrent clinical dilemma in the management of patients with painful metastatic lesions is achieving a balance between effective analgesic therapies versus intolerable side effects, in particular altered mental status. We present the case of an immunosuppressed patient post-lung transplant who was suffering from intractable pain caused by widely metastatic squamous cell carcinoma. The patient's progressive, excruciating neuropathic pain was localized to the area of the left wrist and forearm. Additionally, the patient complained of moderate pain at sites of tumor involvement on her right arm and scalp. Attempts to adequately manage her left upper extremity pain included a combination of pharmacologic treatments intended to treat neuropathic pain (gabapentin, SNRI, ketamine, opioids) and focused regional analgesia (infraclavicular infusion of local anesthetic). However, the patient developed intolerable side effects including altered mental status and delirium associated with the systemic agents and suboptimal control with the infraclavicular infusion. Given that the most severe pain was well localized, we undertook a diagnostic block of the cutaneous nerves of the left forearm. As this intervention significantly reduced her pain, we subsequently performed neurectomies to the left superficial radial nerve, lateral cutaneous nerve of the forearm and the posterior cutaneous nerve of the forearm. This resulted in immediate and continued relief of her left upper extremity pain without an altered mental status. Residual focal pain from lesions over her right arm and scalp was successfully managed with daily topical applications of lidocaine and capsaicin cream. Successful pain control continued until the patient's death five months later.

A comparative microanatomical study on cross-sections of superficial branch of radial nerve in proximal and distal parts of the forearm: a cadaveric study

PURPOSE OF STUDY

Changes in peripheral nerve anatomy with age may be the cause for poor prognosis after nerve repair in elderly cases. The aim of the present study is to find out and compare the cross-sectional microanatomy as well as age-related changes in the non-fascicular components of superficial branch of radial nerve at cubital fossa (SBRN-1) and above wrist (SBRN-2).

METHODS

Thirty-eight fresh human (14 male and five female) cadaveric SBRN-1 and SBRN-2 were collected from both sides of 19 cadavers and study has been performed at different magnifications after routine histological (Masson's trichrome stain) processing was done for morphometric analysis (total cross-sectional area [Asc], fascicular area [Af], non-Af [Anonf], adipose [FAT] area and non-adipose area [nFAT]).

RESULTS

SBRN-1 and SBRN-2 belonged to polyfascicular type and showed difference in amount of connective and adipose tissues in Anonf. The number of fascicles in SBRN-1 ranged from 2 to 6 (3.66±0.21, mean±SEM) and in SBRN-2 ranged from 7.5 to 11.5 (9.24±0.26). On comparing the percentage level of adipose tissue (FAT) in total cross-section area (Asc) and in Anonf of SBRN-1 and SBRN-2, the level of adipose tissue was increased with age.

CONCLUSIONS

The amount of adipose tissue in SBRN-1 and SBRN-2 Anonf was found to be high in most of the elderly cases. On comparison, there was not much difference between SBRN-1 and SBRN-2, but, the fascicle count was found to be increasing gradually from proximal to distal part of the SBRN.