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BioRxiv : the Preprint Server For... Apr 2024Recent studies in vertebrates and have reshaped models of how the axon guidance cue UNC-6/Netrin functions in dorsal-ventral axon guidance, which was traditionally...
Recent studies in vertebrates and have reshaped models of how the axon guidance cue UNC-6/Netrin functions in dorsal-ventral axon guidance, which was traditionally thought to form a ventral-to-dorsal concentration gradient that was actively sensed by growing axons. In the vertebrate spinal cord, floorplate Netrin1 was shown to be largely dispensable for ventral commissural growth. Rather, short range interactions with Netrin1 on the ventricular zone radial glial stem cells was shown to guide ventral commissural axon growth. In , analysis of dorsally-migrating growth cones during outgrowth has shown that growth cone polarity of filopodial extension is separable from the extent of growth cone protrusion. Growth cones are first polarized by UNC-6/Netrin, and subsequent regulation of protrusion by UNC-6/Netrin is based on this earlier-established polarity (the Polarity/Protrusion model). In both cases, short-range or even haptotactic mechanisms are invoked: in vertebrate spinal cord, interactions of growth cones with radial glia expressing Netrin-1; and in a potential close-range interaction that polarizes the growth cone. To explore potential short-range and long-range functions of UNC-6/Netrin, a potentially membrane-anchored transmembrane UNC-6 (UNC-6(TM)) was generated by genome editing. was hypomorphic for dorsal VD/DD axon pathfinding, indicating that it retained some function. Polarity of VD growth cone filopodial protrusion was initially established in , but was lost as the growth cones migrated away from the source in the ventral nerve cord. In contrast, ventral guidance of the AVM and PVM axons was equally severe in and . Together, these results suggest that retains short-range functions but lacks long-range functions. Finally, ectopic expression from non-ventral sources could rescue dorsal and ventral guidance defects in and . Thus, a ventral directional source of UNC-6 was not required for dorsal-ventral axon guidance, and UNC-6 can act as a permissive, not instructive, cue for dorsal-ventral axon guidance. Possibly, UNC-6 is a permissive signal that activates cell-intrinsic polarity; or UNC-6 acts with another signal that is required in a directional manner. In either case, the role of UNC-6 is to polarize the pro-protrusive activity of UNC-40/DCC in the direction of outgrowth.
PubMed: 38712249
DOI: 10.1101/2024.04.23.590737 -
BioRxiv : the Preprint Server For... Apr 2024In quadrupeds, such as cats, cutaneous afferents from the forepaw dorsum signal external perturbations and send signals to spinal circuits to coordinate the activity in...
In quadrupeds, such as cats, cutaneous afferents from the forepaw dorsum signal external perturbations and send signals to spinal circuits to coordinate the activity in muscles of all four limbs. How these cutaneous reflex pathways from forelimb afferents are reorganized after an incomplete spinal cord injury is not clear. Using a staggered thoracic lateral hemisections paradigm, we investigated changes in intralimb and interlimb reflex pathways by electrically stimulating the left and right superficial radial nerves in seven adult cats and recording reflex responses in five forelimb and ten hindlimb muscles. After the first (right T5-T6) and second (left T10-T11) hemisections, forelimb-hindlimb coordination was altered and weakened. After the second hemisection, cats required balance assistance to perform quadrupedal locomotion. Short-, mid- and long-latency homonymous and crossed reflex responses in forelimb muscles and their phase modulation remained largely unaffected after staggered hemisections. The occurrence of homolateral and diagonal mid- and long-latency responses in hindlimb muscles evoked with left and right superficial radial nerve stimulation was significantly reduced at the first time point after the first hemisection, but partially recovered at the second time point with left superficial radial nerve stimulation. These responses were lost or reduced after the second hemisection. When present, all reflex responses, including homolateral and diagonal, maintained their phase-dependent modulation. Therefore, our results show a considerable loss in cutaneous reflex transmission from cervical to lumbar levels after incomplete spinal cord injury, albeit with preservation of phase modulation, likely affecting functional responses to external perturbations.
PubMed: 38712151
DOI: 10.1101/2024.04.23.590723 -
World Journal of Orthopedics Apr 2024De-Quervain's tenosynovitis is a disorder arising from the compression and irritation of the first dorsal extensor compartment of the wrist. Patients who fail...
BACKGROUND
De-Quervain's tenosynovitis is a disorder arising from the compression and irritation of the first dorsal extensor compartment of the wrist. Patients who fail conservative treatment modalities are candidates for surgical release. However, risks with surgery include damage to the superficial radial nerve and an incomplete release due to inadequate dissection. Currently, there is a paucity of literature demonstrating the exact anatomic location of the first dorsal extensor compartment in reference to surface anatomy. Thus, this cadaveric study was performed to determine the exact location of the first extensor compartment and to devise a reliable surgical incision to prevent complications.
AIM
To describe the location of the first dorsal compartment in relation to bony surface landmarks to create replicable surgical incisions.
METHODS
Six cadaveric forearms, including four left and two right forearm specimens were dissected. Dissections were performed by a single fellowship trained upper extremity orthopaedic surgeon. Distance of the first dorsal compartment from landmarks such as Lister's tubercle, the wrist crease, and the radial styloid were calculated. Other variables studied included the presence of the superficial radial nerve overlying the first dorsal compartment, additional compartment sub-sheaths, number of abductor pollicis longus (APL) tendon slips, and the presence of a pseudo-retinaculum.
RESULTS
Distance from the radial most aspect of the wrist crease to the extensor retinaculum was 5.14 mm ± 0.80 mm. The distance from Lister's tubercle to the distal aspect of the extensor retinaculum was 13.37 mm ± 2.94 mm. Lister's tubercle to the start of the first dorsal compartment was 18.43 mm ± 2.01 mm. The radial styloid to the initial aspect of the extensor retinaculum measured 2.98 mm ± 0.99 mm. The retinaculum length longitudinally on average was 26.82 mm ± 3.34 mm. Four cadaveric forearms had separate extensor pollicis brevis compartments. The average number of APL tendon slips was three. A pseudo-retinaculum was present in four cadavers. Two cadavers had a superficial radial nerve that crossed over the first dorsal compartment and retinaculum proximally (7.03 mm and 13.36 mm).
CONCLUSION
An incision that measures 3 mm proximal from the radial styloid, 2 cm radial from Lister's tubercle, and 5 mm proximal from the radial wrist crease will safely place surgeons at the first dorsal compartment.
PubMed: 38709896
DOI: 10.5312/wjo.v15.i4.379 -
Muscle & Nerve May 2024Ultra high-frequency ultrasound (UHFUS) has been demonstrated to allow easy visualization and quantification of median and digital nerve fascicles; however, there is a...
INTRODUCTION/AIMS
Ultra high-frequency ultrasound (UHFUS) has been demonstrated to allow easy visualization and quantification of median and digital nerve fascicles; however, there is a lack of normative data for other upper limb nerves. The purpose of this study was to use UHFUS to establish normative reference values and ranges for fascicle count and density within selected upper extremity nerves.
METHODS
Twenty-one healthy volunteers underwent sonographic examination of the ulnar, superficial branch of the radial, and radial nerves on one upper limb using UHFUS with a 48 MHz linear transducer. The number of fascicles in each peripheral nerve and fascicle density were assessed.
RESULTS
The mean fascicle number and fascicle density for each of the measured nerves was ulnar nerve at the wrist 11.7 and 2.0, ulnar nerve at the elbow 9.2 and 1.1, superficial branch of the radial nerve 7.3 and 2.5, and radial nerve at the spiral groove 4.2 and 0.8. A single significant association was observed between CSA and fascicle number in the ulnar nerve at the wrist (p = .023, r = 0.66). Neither fascicle number nor density could be predicted by age, sex, height, weight, or body mass index.
DISCUSSION
UHFUS may help to establish a baseline of normative data on upper limb nerves that are not frequently biopsied due to their mixed motor and sensory functions and has the potential for increased understanding of nerve fascicular anatomy to improve diagnostic accuracy of focal nerve lesions, particularly those with selective fascicular involvement.
PubMed: 38708872
DOI: 10.1002/mus.28097 -
JSES International May 2024The number of malignant tumors is increasing as are bone metastases, such as those in the humerus. Arm function is important for an independent everyday life. In this...
BACKGROUND
The number of malignant tumors is increasing as are bone metastases, such as those in the humerus. Arm function is important for an independent everyday life. In this study, compound osteosynthesis of metastatic fractures of the humerus is examined for its suitability in light of the competing risk of death.
METHODS
This retrospective monocentric study includes a cohort of tumor patients who underwent primary compound osteosynthesis for pathological humeral fractures. The main endpoint was the continued existence of compound osteosynthesis using competing risk analysis to contrast failure and death. Failure was defined as mechanical failure of the osteosynthesis construct like refracture or plate-and-screw dislocation or loosening, which provides an indication for reintervention. Other complications are also described.
RESULTS
We included 36 consecutive patients (64% male, mean age: 71.6 yr) from September 2007 to October 2020. In 58% of the cases, the left humerus was fractured. Lung carcinoma was the most common cause of bone metastases (27.8%). Compound osteosynthesis was performed with a median delay of 5 days after diagnosis of the pathologic fracture. Postoperative complications occurred in 7 of the 36 patients (19.4%): radial nerve palsy (n = 3), postoperative hematoma (n = 2), refracture (n = 2), and screw loosening (n = 1). Few mechanical failures (8.3%) occurred within the first year; only 1 patient needed revision of the osteosynthesis (2.8%). Median patient survival after compound osteosynthesis was 26.6 weeks. Competing risk analysis showed that for up to 2 years, the risk of death is clearly dominant over the risk of osteosynthesis failure from surgery.
CONCLUSION
Our study shows that compound osteosynthesis of the humerus is a suitable option for patients with pathologic humerus fractures. Compound osteosynthesis of the humerus usually survives the duration of malignant tumor disease.
PubMed: 38707561
DOI: 10.1016/j.jseint.2023.12.002 -
JSES Reviews, Reports, and Techniques May 2024
PubMed: 38706677
DOI: 10.1016/j.xrrt.2024.01.006 -
Journal of Plastic, Reconstructive &... Jun 2024Many surgical strategies aim to treat the symptomatic neuroma of the superficial branch of the radial nerve (SBRN). It is still difficult to treat despite many attempts...
BACKGROUND
Many surgical strategies aim to treat the symptomatic neuroma of the superficial branch of the radial nerve (SBRN). It is still difficult to treat despite many attempts to reveal a reason for surgical treatment failure. The lateral antebrachial cutaneous nerve (LACN) is known to overlap and communicate with SBRN. Our study aims to determine the frequency of spreading of LACN fibers into SBRN branches through a microscopic dissection to predict where and how often LACN fibers may be involved in SBRN neuroma.
METHODS
Eighty-seven cadaveric forearms were thoroughly dissected. The path of LACN fibers through the SBRN branching was ascertained using microscopic dissection. Distances between the interstyloid line and entry of LACN fibers into the SBRN and emerging and bifurcation points of the SBRN were measured.
RESULTS
The LACN fibers joined the SBRN at a mean distance of 1.7 ± 2.5 cm proximal to the interstyloid line. The SBRN contained fibers from the LACN in 62% of cases. Most commonly, there were LACN fibers within the SBRN's third branch (59%), but they were also observed within the first branch, the second branch, and their common trunk (21%, 9.2%, and 22%, respectively). The lowest rate of the LACN fibers was found within the SBRN trunk (6.9%).
CONCLUSION
The SBRN contains LACN fibers in almost 2/3 of the cases, therefore, the denervation of both nerves might be required to treat the neuroma. However, the method must be considered based on the particular clinical situation.
Topics: Humans; Neuroma; Radial Nerve; Cadaver; Female; Male; Aged; Middle Aged; Forearm; Aged, 80 and over; Nerve Fibers; Peripheral Nervous System Neoplasms; Dissection
PubMed: 38703710
DOI: 10.1016/j.bjps.2024.04.008 -
Handbook of Clinical Neurology 2024Electrodiagnostic testing (EDX) has been the diagnostic tool of choice in peripheral nerve disease for many years, but in recent years, peripheral nerve imaging has been... (Review)
Review
Electrodiagnostic testing (EDX) has been the diagnostic tool of choice in peripheral nerve disease for many years, but in recent years, peripheral nerve imaging has been used ever more frequently in daily clinical practice. Nerve ultrasound and magnetic resonance (MR) neurography are able to visualize nerve structures reliably. These techniques can aid in localizing nerve pathology and can reveal significant anatomical abnormalities underlying nerve pathology that may have been otherwise undetected by EDX. As such, nerve ultrasound and MR neurography can significantly improve diagnostic accuracy and can have a significant effect on treatment strategy. In this chapter, the basic principles and recent developments of these techniques will be discussed, as well as their potential application in several types of peripheral nerve disease, such as carpal tunnel syndrome (CTS), ulnar neuropathy at the elbow (UNE), radial neuropathy, brachial and lumbosacral plexopathy, neuralgic amyotrophy (NA), fibular, tibial, sciatic, femoral neuropathy, meralgia paresthetica, peripheral nerve trauma, tumors, and inflammatory neuropathies.
Topics: Humans; Electrodiagnosis; Magnetic Resonance Imaging; Peripheral Nervous System Diseases; Ultrasonography
PubMed: 38697740
DOI: 10.1016/B978-0-323-90108-6.00001-6 -
Handbook of Clinical Neurology 2024Radial neuropathy is the third most common upper limb mononeuropathy after median and ulnar neuropathies. Muscle weakness, particularly wrist drop, is the main clinical... (Review)
Review
Radial neuropathy is the third most common upper limb mononeuropathy after median and ulnar neuropathies. Muscle weakness, particularly wrist drop, is the main clinical feature of most cases of radial neuropathy, and an understanding of the radial nerve's anatomy generally makes localizing the lesion straightforward. Electrodiagnosis can help confirm a diagnosis of radial neuropathy and may help with more precise localization of the lesion. Nerve imaging with ultrasound or magnetic resonance neurography is increasingly used in diagnosis and is important in patients lacking a history of major arm or shoulder trauma. Radial neuropathy most often occurs in the setting of trauma, although many other uncommon causes have been described. With traumatic lesions, the prognosis for recovery is generally good, and for patients with persistent deficits, rehabilitation and surgical techniques may allow substantial functional improvement.
Topics: Humans; Radial Neuropathy; Radial Nerve
PubMed: 38697735
DOI: 10.1016/B978-0-323-90108-6.00015-6 -
American Journal of Physical Medicine &... Apr 2024The aim of this study was to characterize the electrodiagnostic findings of radial neuropathy using motor segmental conduction study (RMSCS), and to determine the...
OBJECTIVE
The aim of this study was to characterize the electrodiagnostic findings of radial neuropathy using motor segmental conduction study (RMSCS), and to determine the utility of subsequent inching test in precise lesion localization.
DESIGN
Twenty-three patients with radial neuropathy were evaluated using RMSCS with three-point stimulation. The pathomechanism of the lesions according to the RMSCS was classified into three groups: conduction block (CB), mixed lesion (combination of CB and axonal degeneration), and axonal degeneration. Inching test was performed in patients with CB to localize the lesion site, and needle EMG identified the most proximal radial nerve-innervated muscles affected.
RESULTS
Out of twenty-three cases, the RMSCS demonstrated probable partial CB in 10, mixed lesions in 2, and axonal degeneration in 10. One case could not be categorized with RMSCS alone. As determined by RMSCS and inching test, the most common cause of CB was compression, while the most common cause of axonal degeneration was iatrogenic. In the CB group, the lesion locations identified by RMSCS and inching test were consistent with needle EMG localization.
CONCLUSION
The combined RMSCS and inching test technique can precisely localize radial motor nerve injuries and provide detailed information on electrodiagnostic characteristics of radial mononeuropathy.
PubMed: 38686822
DOI: 10.1097/PHM.0000000000002505