The Musculocutaneous Nerve: Ultrasound Appearance for Peripheral Nerve Block

Eliciting tactile sensations in the hand through non-invasive proximal nerve stimulation: a feasibility study

Recently, non-invasive proximal nerve stimulation has been widely investigated to restore tactile sensations. It has been demonstrated that tactile sensations in the hand could be elicited by nerve stimulation on the upper arm. However, it is still unknown whether tactile sensations could be elicited by stimulation at a proximal location close to the neck. In this study, non-invasive proximal nerve stimulation tests were performed to elicit tactile sensations in the hand of subjects. Six Ag/AgCl gel electrodes (2 × 3) were placed on the supraclavicular fossa where the proximal parts of the brachial plexus nerves were located. Then, fifteen potential electrode pairs were tested to explore whether tactile sensations could be elicited by non-invasive proximal nerve stimulation. Eight able-bodied subjects (male) were recruited to participate in the test. The stimulated sensation regions in the hand and the sensory intensity were reported and recorded during the experiment. The results demonstrated that the tactile sensations in various regions in the hand could be elicited through non-invasive nerve stimulation at the proximal location close to the neck.

Ultrasonographic study of a modified axillary approach to block the major branches of the brachial plexus in dogs

OBJECTIVE

To provide ultrasonographic mapping of the axillary region of dogs to facilitate identification of the major branches of the brachial plexus in relation to the axillary artery.

STUDY DESIGN

Prospective study.

ANIMALS

A total of two dog cadavers and 50 client-owned, healthy dogs weighing >15 kg.

METHODS

In Phase 1, anatomical dissections were performed to identify the relation of the major brachial plexus nerves to the axillary artery. In Phase 2, with the dogs in dorsal recumbency with thoracic limbs flexed naturally, the axillary space was scanned using a linear array probe oriented on the parasagittal plane until the axis transverse to nerves was found. Then, the transducer was rotated to a slight lateral angle approximately 30° to midline. The examination aimed to identify the axillary artery and the musculocutaneous, radial, median and ulnar nerves in addition to determining their position and distribution in four predefined sectors.

RESULTS

The musculocutaneous nerve was observed in all animals cranial to the axillary artery. The radial, ulnar and median nerves were distributed around the axillary artery, with >90% on the caudal aspect of the axillary artery (sectors 1 and 2).

CONCLUSIONS AND CLINICAL RELEVANCE

Ultrasonography identified the location of the brachial plexus nerves near the studied sectors, providing useful guidance for performing a brachial plexus nerve block.

Proximal RUMM block in dogs: preliminary results of cadaveric and clinical studies

OBJECTIVE

To design and assess the perioperative analgesic efficacy of an ultrasound (US)-guided radial (R), ulnar (U), median (M) and musculocutaneous (Mc) nerve blocks, performed together in the axillary space by a single, in-plane approach.

STUDY DESIGN

Anatomical research and prospective clinical study.

ANIMALS

A group of three dog cadavers and 15 client-owned dogs undergoing orthopaedic thoracic limb surgery.

METHODS

Phase 1: Anatomical dissection and US study of the axillary space were performed to design the US-guided proximal RUMM block. The technique was considered successful if a total volume of 0.15 mL kg-1 new methylene blue solution completely stained the four nerves in two cadavers for ≥2 cm. Phase 2: In 15 client-owned dogs undergoing orthopaedic thoracic limb surgery, the RUMM block designed in phase 1 was performed to provide analgesia using a total volume of 0.15 mL kg-1 of ropivacaine 0.5%. The block was considered effective if the intraoperative fentanyl requirement was <1.2 mcg kg-1 hour-1 and until the postoperative pain score was [short-form Glasgow Composite Measure Pain Scale (SF-GCMPS)] ≤5/20.

RESULTS

Phase1: Detection of the four nerves was always feasible in a single US-window. The axillary artery and Mc nerve were used as landmarks. In-plane needling approach was feasible in both cadavers. All the nerves were completely stained for >2 cm. No intrathoracic dye spread was found. Phase 2: In 14/15 anaesthetized dogs, mean intraoperative fentanyl requirement was 0.25 ± 0.05 mcg kg-1 hour-1. Postoperatively, all dogs had SF-GCMPS ≤5/20 up to 8 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

The US-guided proximal RUMM block performed at the axillary level with a single, in-plane needling approach using 0.15 mL kg-1 of ropivacaine 0.5% minimized fentanyl requirement during thoracic limb surgery, contributing to postoperative analgesia up to 8 hours after execution of the peripheral nerve block.

Imaging in the diagnosis of ulnar nerve pathologies-a neoteric approach

The ulnar nerve is a branch of the C8 and T1 nerve roots and arises from the medial cord of the brachial plexus. It supplies the intrinsic muscles of the hand and assists the median nerve in functioning of the flexors. Also known as the musician’s nerve, it is the second most common nerve involved in compressive neuropathy following the median nerve. Common sites of entrapment include cubital tunnel at the elbow, the ulnar groove in the humerus and the Guyon’s canal at the wrist. Patients present with altered sensation in the ulnar fourth and the fifth digit and the medial side of arm with loss of function of intrinsic muscles of the hand, the flexor carpi ulnaris and ulnar fibres of flexor digitorum superficialis in more severe cases. Diagnosis relies on clinical examination, electrodiagnostic studies and imaging findings. Plain radiographs are used to identify fracture sites, callus, or tumours as cause of compression. Technological advances in ultrasonography have allowed direct visualisation of the involved nerve with assessment of exact site, extent and type of injury. It yields unmatched information about anatomical details of the nerve. MR imaging adds to soft tissue details and helps in characterising the lesion. This pictorial review aims to illustrate a wide spectrum of causes of ulnar neuropathies as seen on ultrasound and MRI and emphasises upon the importance of imaging modalities in the diagnosis of neuropathies.

A panorama of radial nerve pathologies- an imaging diagnosis: a step ahead

Abstract

The radial nerve has a long and tortuous course in the upper limb. Injury to the nerve can occur due to a multitude of causes at many potential sites along its course. The most common site of involvement is in the proximal forearm affecting the posterior interosseous branch while the main branch of the radial nerve is injured in fractures of the humeral shaft. Signs and symptoms of radial neuropathy depend upon the site of injury. Injury to the nerve distal to innervation of triceps brachii results in loss of extensor function with sparing of function of the triceps resulting in the characteristic ‘wrist drop’. Injury in the mid-arm is associated with loss of sensation in the dorsolateral aspect of the hand, the dorsal aspect of the radial three-and-a-half digits and in the first web space. Involvement of only the posterior interosseous nerve (PIN) results in weakness of the wrist and digit extensors. Diagnosis relies on clinical examination, electrodiagnostic studies and imaging findings. Plain radiographs are used to identify fracture sites, callus or tumours as cause of compression. Technological advances in ultrasonography have allowed direct visualisation of the involved nerve with assessment of the exact site, extent and type of injury. It yields unmatched information about anatomical details of the nerve. MR imaging adds to soft-tissue details and helps in characterising the lesion. This pictorial review aims to illustrate a wide spectrum of causes of radial neuropathy and emphasises the importance of imaging modalities in diagnosis of neuropathies.

Teaching Points

• Radial nerve injuries are assessed by clinical examination and diagnosed using electrodiagnostic and imaging studies.

• Knowledge of anatomical relations and course of the nerve is necessary to identify the nerve at pre-determined anatomical locations.

• Altered echogenicity and signal intensity, discontinuity of the nerve, focal thickening and cause of compression can be assessed by imaging modalities.

• MR imaging helps in confirmation of the ultrasound findings, differentiating similar appearing lesions and provides additional soft-tissue details.

High-resistance strength training does not affect nerve cross sectional area - An ultrasound study

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Trained individuals did not have larger cross-sectional area of peripheral nerves than untrained individuals.

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Trained individuals had thicker biceps muscles.

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Nerve CSA of the median nerve in the forearm correlated with participants’ height, and was larger in men than women.

Objective

The aim was to study the effect of high-resistance strength training on peripheral nerve morphology, by examining properties of peripheral nerves as well as distal and proximal muscle thickness with ultrasound, comparing healthy individuals who perform and do not perform high-resistance strength training.

Methods

Neuromuscular ultrasound was used to examine cross sectional area (CSA) of the median and musculocutaneous nerves, and muscle thickness of the abductor pollicis brevis muscle, biceps brachii muscle, quadriceps muscle and extensor digitorum brevis muscle, in 44 healthy individuals, of whom 22 performed regular high-resistance strength training.

Results

No difference in nerve CSA was found between trained and untrained individuals although trained individuals had thicker biceps brachii muscles. The CSA of the median nerve in the forearm correlated with participants’ height and was significantly larger in men than women.

Conclusions

In this cohort, CSA of the median and musculocutaneous nerves was not affected by strength training, whereas gender had a prominent effect both on CSA and muscle thickness.

Significance

This is the first study to examine the effect of high-resistance strength training on peripheral nerves with neuromuscular ultrasound.

Ultrasound-Guided Musculocutaneous Nerve Block in Postherpetic Neuralgia

Postherpetic neuralgia is a common and challenging complication of herpes zoster infection, particularly in older people. In recent decades, first-line treatments, including oral or topical medication, have become well established. However, few studies have reported the efficacy of interventional procedures for the treatment of postherpetic neuralgia. Here, the authors present a case of intractable postherpetic neuralgia treated with musculocutaneous peripheral nerve block under ultrasound guidance. Symptoms remained controlled at 1 mo follow-up. Ultrasound can be readily applied to improve the accuracy and efficiency of peripheral nerve block as it is currently widely used to evaluate the musculoskeletal system in clinical settings.

Ultrasound-guided anterior axilla musculocutaneous nerve block

PURPOSE

This paper presents a technique of ultrasound-guided localisation and block of the musculocutaneous nerve through the anterior wall of the axilla.

MATERIALS AND METHODS

Twenty patients (7 males and 13 females; mean age, 35 years) had axillary nerve block for upper extremity trauma. With the arm adducted, the ultrasound probe was positioned on the anterior axillary wall; the axillary artery, coracobrachialis and pectoralis major muscles and lateral cord of brachial plexus were visualised in cross section. With continuous imaging of the axillary artery in cross section, the ultrasound probe was slowly moved towards the biceps muscle until the musculocutaneous nerve appeared crossing the coracobrachialis muscle. After ultrasound localisation of the musculocutaneous nerve, the arm was abducted and externally rotated, and the nerve was identified with nerve stimulation and blocked. The quality of sensory and motor nerve block, as well as of ultrasound imaging were evaluated.

RESULTS

Ultrasound-guided block of the musculocutaneous nerve was excellent and complete in 18 of the 20 patients. In two patients, the musculocutaneous nerve was fused with the median nerve and the nerve block was repeated successfully with the same technique. The quality of ultrasound imaging was excellent in all patients. No patient experienced pain or tourniquet discomfort during surgery, or any other nerve block-related complication.

CONCLUSION

The anterior axillary ultrasound view provides for complete nerve block and imaging of the entire course of the musculocutaneous nerve and its relations with adjacent structures with excellent quality.

Extracting structural features of rat sciatic nerve using polarization-sensitive spectral domain optical coherence tomography

We present spectral domain polarization-sensitive optical coherence tomography (SD PS-OCT) imaging of peripheral nerves. Structural and polarization-sensitive OCT imaging of uninjured rat sciatic nerves was evaluated both qualitatively and quantitatively. OCT and its functional extension, PS-OCT, were used to image sciatic nerve structure with clear delineation of the nerve boundaries to muscle and adipose tissues. A long-known optical effect, bands of Fontana, was also observed. Postprocessing analysis of these images provided significant quantitative information, such as epineurium thickness, estimates of extinction coefficient and birefringence of nerve and muscle tissue, frequency of bands of Fontana at different stretch levels of nerve, and change in average birefringence of nerve under stretched condition. We demonstrate that PS-OCT combined with regular-intensity OCT (compared with OCT alone) allows for a clearer determination of the inner and outer boundaries of the epineurium and distinction of nerve and muscle based on their birefringence pattern. PS-OCT measurements on normal nerves show that the technique is promising for studies on peripheral nerve injury.

US imaging of the musculocutaneous nerve

PURPOSE

To describe the potential value of high-resolution sonography for evaluation of the musculocutaneous nerve (MCN).

MATERIALS AND METHODS

The normal anatomy of the MCN was evaluated on three cadaveric limbs and correlated with the US images obtained in 15 healthy subjects. Seven consecutive patients with MCN neuropathy were then evaluated with sonography using 17.5 and 12.5-MHz broadband linear array transducers. All patients had abnormal nerve conduction studies and underwent correlative MR imaging on a 1.5-T system.

RESULTS

One-to-one comparison between cadaveric specimens and sonographic images showed that the MCN can be reliably identified from the axilla through the elbow, including the lateral antebrachial cutaneous (LAbC) nerve. In the patients group with MCN neuropathy, sonography allowed detection of a wide spectrum of abnormalities. In 5/7 cases, a spindle neuroma was depicted in continuity with the nerve. In one case, US identified focal swelling of the nerve and in another case US was negative. The neuroma was hyperintense on T2-weighted sequences in 75% of cases. In one patient, the nerve showed Gd-enhancement on fat-suppressed T1-weighted sequences. The nerve was never detected on unenhanced T1-scans. Owing to its small-size and out-of-plane course, the MCN may be more reliably depicted with sonography rather than with MR imaging.

CONCLUSIONS

US is promising for evaluating traumatic injuries of the MCN. By providing unique information on the entire course of the nerve, US can be used as a valuable complement of clinical and electrophysiologic findings.

Is the musculocutaneous nerve really in the coracobrachialis muscle when performing an axillary block? An ultrasound study

BACKGROUND

In reference textbooks describing axillary block, the ulnar, radial, and median nerves are located in a common sheath surrounding the axillary artery. In contrast, the musculocutaneous nerve is described as lying outside this sheath in the coracobrachialis muscle. In a recent case report of ultrasound-guided axillary block, the musculocutaneous nerve was joined to the median nerve outside this muscle. Our study evaluated the prevalence of atypical musculocutaneous nerve localizations during axillary block.

METHODS

All patients undergoing ultrasound-guided axillary block were included from December 2006 to December 2008. Before needle insertion, musculocutaneous, median, ulnar, and radial nerves were localized using ultrasound. Nerve stimulation confirmed atypical nerve localization. After injection of local anesthetics, musculocutaneous and median nerve anatomical relationships were observed.

RESULTS

The musculocutaneous nerve was outside the coracobrachialis muscle in 83 of the 387 analyzed blocks (22%). It was near the axillary artery in 22 cases (6%). The musculocutaneous and median nerves appeared as a common neural structure in 61 cases (16%). After local anesthetic injection, a common trunk persisted in 16 of 61 cases (26%), musculocutaneous and median nerves separated in 37 cases (61%), and 2 roots of the median nerve appeared (with or without a separated musculocutaneous nerve) in 6 cases (10%). Two cases (3%) remained undefined. Ulnar nerve location of the 83 patients with atypical musculocutaneous nerve position differed from the ones with a classical musculocutaneous nerve localization.

CONCLUSIONS

During axillary block, the musculocutaneous nerve is outside the coracobrachialis muscle in 1 of 5 patients. This atypical location should be considered during performance of axillary blockade to avoid repeated IM puncture.

Soft tissue landmark for ultrasound identification of the sciatic nerve in the infragluteal region: the tendon of the long head of the biceps femoris muscle

BACKGROUND AND OBJECTIVES

The sciatic nerve block represents one of the more difficult ultrasound-guided nerve blocks. Easy and reliable internal ultrasound landmarks would be helpful for localization of the sciatic nerve. Earlier, during ultrasound-guided posterior approaches to the infragluteal sciatic nerve, the authors recognized a hyperechoic structure at the medial border of the long head of biceps femoris muscle (BFL). The present study was performed to determine whether this is a potential internal landmark to identify the infragluteal sciatic nerve.

METHODS

The depth and the thickness of this hyperechoic structure, its relationship with the sciatic nerve and the ultrasound visibility of both were recorded in the proximal upper leg of 21 adult volunteers using a linear ultrasound probe in the range of 7-13 MHz. The findings were verified by an anatomical study in two cadavers.

RESULTS

The hyperechoic structure at the medial border of the BFL extended in a dorsoventral direction between 1.4+/-0.6 cm (mean+/-SD) and 2.8+/-0.8 cm deep from the surface, with a width of 2.2+/-0.9 mm. Between 2.6+/-0.9 and 10.0+/-1.5 cm distal to the subgluteal fold, the sciatic nerve was consistently identified directly at the ventral end of the hyperechoic structure in all volunteers. The anatomical study revealed that this hyperechoic structure corresponds to tendinous fibres inside and at the medial border of the BFL.

CONCLUSION

The hyperechoic BFL tendon might be a reliable soft tissue landmark for ultrasound localization of the infragluteal sciatic nerve.

[Ultrasound guidance in pediatric regional anesthesia]

Ultrasound imaging is being used to guide pediatric nerve block procedures. Difficulties that arise because of the smaller anatomical structures in children can be compensated for by the greater aqueous consistency and reduced calcification. Given the shorter distance between the surface of the skin and nerves, it is advisable to use a linear array transducer working at a high frequency (7-10 MHz). Like adults, children benefit when ultrasound guidance is used in the performance of neuraxial nerve trunk blocks, particularly of the umbilical and ilioinguinal nerves, and in greater measure in spinal blocks. Ultrasound guidance enhances efficacy and also affords the important advantage of greater safety. The main disadvantages are the cost of equipment and the necessary learning curve.

Ultrasound-guided block of the brachial plexus at the humeral canal

PURPOSE

Conduction block of the brachial plexus block at the humeral canal, as described by Dupre, has certain clinical indications. The aim of this preliminary study was to assess the feasibility of this technique under ultrasound guidance.

METHODS

After ultrasound evaluation of the brachial plexus at the humeral canal in 61 adult volunteers, we performed ultrasound-guided blocks in another 20 adult patients. A linear 38 mm probe, 13-6 MHz, and a 50-mm insulated block needle were used to guide injection of lidocaine 1.5% with epinephrine.

RESULTS

Ulnar and median nerves are superficial and located at similar depths. Ultrasound imaging showed the musculocutaneous nerve to be located dorsally. The radial nerve is dorsal to the plane of the musculocutaneous nerve. Relative to the brachial artery, the median nerve is situated between 12 and 1 o'clock in 66% of the cases. Relative to the basilic vein, the ulnar nerve is situated at 3 o'clock in 46% of the cases. The evaluated block sequence was radial, ulnar, musculocutaneous and median nerve; two points of puncture were mandatory, and 6.85 +/- 0.37 min were required to perform the blocks. Sensory onset times were similar for the four nerves. Injectate volume was lower for the musculocutaneous nerve compared to other nerves (P < 0.05). All 20 patients experienced complete sensory and motor blocks.

CONCLUSION

We describe an approach to, and the feasibility of ultrasound-guided block of the brachial plexus at the humeral canal. Further study will be required to establish the effectiveness and the safety of this technique.

Cross-sectional area reference values for nerve ultrasonography

Ultrasound allows for a non-invasive structural assessment of nerves, muscles, and surrounding tissues, and therefore it is increasingly being used as a supplement to traditional electrodiagnostic studies. As investigators have begun to use ultrasound to explore peripheral nerves, it has become clear that conditions such as entrapment, hereditary neuropathies, acquired neuropathies, trauma, and nerve tumors result in an increase in nerve cross-sectional area. Reference values have not been published for the cross-sectional area of many nerves commonly studied in diseases of the peripheral nervous system, so our goal was to obtain reference values for the nerve cross-sectional area at the following sites: radial at antecubital fossa; radial at distal spiral groove; musculocutaneous in upper arm; trunks of the brachial plexus; vagus at carotid bifurcation; sciatic in distal thigh; tibial in popliteal fossa; tibial in proximal calf; tibial at ankle; peroneal in popliteal fossa; peroneal at fibular head; and sural in distal calf. Mean cross-sectional area, as well as side-to-side differences, are reported for each site, and qualitative data are provided to guide imaging at each site. The information provided in this study should serve as the starting point for quantitatively evaluating these nerve sites with ultrasound.

[Portable ultrasound devices in regional anesthesia: the brachial plexus block]

Ultrasonography has received increasing attention in regional anesthesia in recent years because it allows visualization of the nerves, the needle, and the surrounding structures and makes it possible to monitor distribution of the local anesthetic. Ultrasound technology is unfamiliar to most anesthesiologists, unless they work with transesophageal echocardiography. Ultrasound-guided regional anesthesia relies entirely on the expertise of the person performing the technique and how that person interprets the images, though the latest portable ultrasound devices are ergonomically designed for fast, easy use, even by less experienced personnel. The high-frequency probes can identify the brachial plexus and produce excellent images of considerable educational value that differ only slightly from those provided by larger, more expensive equipment. Ultrasonography makes it possible to identify the brachial plexus, from the roots to the peripheral nerves of the arm. We describe the main approaches used in providing an ultrasound-guided brachial plexus block and explain the basic principles of ultrasound imaging.

Effects of the adducted or abducted position of the arm on the course of the musculocutaneous nerve during anterior approaches to the shoulder

Nerve injury is a common complication during anterior shoulder surgery. The purpose of the study was to evaluate the musculocutaneous nerve (MN) anatomically and to clarify the relationship of the MN to the glenoid labrum and coracoid process in different arm positions. The study was carried out on 40 shoulders of 20 adult cadavers fixed in 10% formaldehyde. The minimum distance of the MN at the entrance point of the nerve into the coracobrachialis to the anteromedial aspect of the coracoid tip and the distance between the MN and the top, middle, and inferior points of the glenoid labrum were measured. All measurements were performed with a digital caliper while the arm was in a neutral position, 45 degrees and 90 degrees of abduction, 90 degrees of abduction-internal rotation and 90 degrees of abduction-external rotation to evaluate whether arm position effects the results statistically or not. The results demonstrated that the position of the arm significantly changes the distance between the coracoid process (CP) and the MN or its cord. The change in distance between the glenoid labrum and the MN or its cord was also statistically significant. The distance between the CP and MN was greatest when the arm was abducted to 45 degrees (mean 3.4 cm) and least when the arm was positioned to 90 degrees of abduction-internal rotation (mean 2.0 cm). While the distance between the MN and the coracoid process was least at 90 degrees of abduction and internal rotation, the distance between the MN and glenoid labrum was lest with 90 degrees of abduction and external rotation. The distance between the glenoid labrum and MN was greatest with 45 degrees of abduction. The results of this study might be of use in avoiding the MN especially during Bristlow operations and certain rotator cuff procedures. Transferring the coracoid process during Bristow operations or placing arthroscopic portals when the arm is abducted to 45 degrees appears to be the safest position in terms of MN injury. Based on our results, when the arm needs to be abducted to 90 degrees during operation, externally rotating it may decrease the tension on the brachial plexus thus increasing the distance between the MN and the portals or retractors.

Variant location of the musculocutaneous nerve during axillary nerve block

We present the case of a 56-year-old man who underwent axillary nerve block for a wrist arthroscopy procedure, with real-time ultrasound and peripheral nerve stimulator guidance. The ulnar nerve and radial nerve were located medial and posterior to the brachial artery, respectively. A large complex structure was noted in the position typically occupied by the median nerve. Contact of this structure with the stimulating needle produced strong biceps contraction, and slight adjustment of the needle resulted in forearm pronation. After injection of 10 mL of local anesthetic near this structure, it appeared to consist of two separate components on ultrasound. We believe that these components represented the median and musculocutaneous nerves lying together, lateral to the artery. Radial, median, ulnar, and musculocutaneous nerve block ensued, and wrist arthroscopy was carried out uneventfully. Knowledge of this anatomical variation may improve anesthesiologists' ability to provide effective axillary block.