Ultrasound Anatomy of the Radial Nerve in the Distal Upper Arm:

Safe zone for lateral pin placement for external fixation of the distal humerus

External fixation is a common, efficient technique used for humeral shaft stabilization and elbow fractures. There are reports of radial nerve injuries associated with this procedure. In this study, we investigated the course and variability of the radial nerve along the lateral humerus in relation to the elbow joint to determine a relatively safe zone for lateral pin placement in external fixation. Twenty upper extremities from 10 cadavers were studied. The nerve branches and course of the radial nerve along the lateral humerus were carefully dissected. Straight lines (a, b, and c) were made connecting three landmarks (the acromion, coracoid process, and anterior wall of the axilla) in the proximal upper extremity to the lateral condyle (LC) of the humerus; their intersections with the radial nerve (A, B, and C) were marked. We analyzed whether the intersection positions were correlated with the connecting line lengths. The mean lengths of the connecting lines were (a) 27.24 ± 2.57, (b) 26.18 ± 2.79, and (c) 20.95 ± 1.44 cm; the distance between the intersection points and the LC of the humerus were (Aa) 7.56 ± 1.31, (Bb) 6.90 ± 2.27, and (Cc) 5.01 ± 0.83 cm; and the measured intersection points of the radial nerve in the lateral aspect of the humerus were (A) 18.48%-34.82%, (B) 13.48%-40.00%, and (C) 19.27%-28.05% of the lengths of lines a, b, and c, respectively. Our data provide a more reliable reference to predict the course of the radial nerve on the lateral humerus and define a safe zone for pin placement. Clin. Anat., 33:637-642, 2020. © 2019 Wiley Periodicals, Inc.

Ultrasonographic evaluation of radial nerve injuries associated with pediatric chronic monteggia lesions

INTRODUCTION

To determine the ultrasonographic evaluation of the radial nerve (RN) before correction of chronic pediatric Monteggia lesions in patients with suspected nerve injury.

METHODS

Twelve consecutive children with Monteggia lesions were investigated. The cross-sectional area (CSA) of the nerve and the nerve-to-skin (N-S) distance were determined by ultrasonography at 3 levels: 5 cm proximal to the humeroradial joint (L_prox), a horizontal line through the humeroradial joint (L_mid), and 2.5 cm distal to the humeroradial joint (L_dist).

RESULTS

The CSA was greater on the injured side than on the unaffected side at L_prox and at L_mid (P < 0.01), but no difference was noted for posterior interosseous nerve (PIN) at L_dist (P = 0.445). The N-S values were greater on the unaffected side than on the injured side (P < 0.01), but there was no difference at L_dist in superficial RN and PIN.

DISCUSSION

Ultrasonography allowed the preoperative assessment of the severity of RN injuries in chronic pediatric Monteggia lesions. Muscle Nerve 59:326-330, 2019.

Pulsed radiofrequency on radial nerve under ultrasound guidance for treatment of intractable lateral epicondylitis

Lateral epicondylitis is a painful and functionally limiting disorder. Although lateral elbow pain is generally self-limiting, in a minority of people symptoms persist for a long time. When various conservative treatments fail, surgical approach is recommended. Surgical denervation of several nerves that innervate the lateral humeral epicondyle could be considered in patients with refractory pain because it denervates the region of pain. Pulsed radiofrequency is a minimally invasive procedure that improves chronic pain when applied to various neural tissues without causing any significant destruction and painful complication. This procedure is safe, minimally invasive, and has less risk of complications relatively compared to the surgical approach. The radial nerve can be identified as a target for pulsed radiofrequency lesioning in lateral epicondylitis. This innovative method of pulsed radiofrequency applied to the radial nerve has not been reported before. We reported on two patients with intractable lateral epicondylitis suffering from elbow pain who did not respond to nonoperative treatments, but in whom the ultrasound-guided pulsed radiofrequency neuromodulation of the radial nerve induced symptom improvement. After a successful diagnostic nerve block, radiofrequency probe adjustment around the radial nerve was performed on the lateral aspect of the distal upper arm under ultrasound guidance and multiple pulsed treatments were applied. A significant reduction in pain was reported over the follow-up period of 12 weeks.

Radial nerve measurements in nonsymptomatic upper extremities of Filipinos: A cross-sectional study

INTRODUCTION

Despite reports on the association of radial nerve (RN) size and lateral epicondylalgia (LE), Filipino normative values on RN size in healthy elbows are not established. An association with upper extremity anthropometric measurements is likewise not reported.

METHODS

Musculoskeletal ultrasound measurements of the RN at the level of the lateral epicondyle (RN-LE), posterior interosseous nerve at the level of the radial head and supinator (PIN-RH and PIN-sup), and superficial RN (SRN) in the elbows of healthy Filipinos were made in Manila from January-September 2011.

RESULTS

A total of 198 elbows of 99 healthy participants aged 43 years (range, 33-48 years) [median(IQR)] were investigated. Men have larger PIN-RH, PIN-sup, and SRN compared with women. Arm length was associated with PIN-RH, PIN-sup, and SRN (P < 0.05). Activities and elbow circumference measurements (at 2 levels) were associated with PIN-RH.

CONCLUSIONS

RN reference values can now be used for comparison in elbows with LE.

Safe zone for superolateral entry pin into the distal humerus in children: an MRI analysis

BACKGROUND

The radial nerve is at risk for iatrogenic injury during placement of pins, screws, or wires around the distal humerus. Unlike adults, detailed anatomic information about the relationship of the nerve to the distal humerus is lacking in children.

QUESTION/PURPOSES

This study evaluates the relationship of the radial nerve to the distal humerus in a pediatric population on conventional MRI and proposes an anatomic safe zone using easily identifiable bony landmarks on an AP elbow radiograph.

METHODS

To determine the course of the radial nerve at the lateral distal humerus, we reviewed 23 elbow radiographs and MRIs of 22 children (mean age, 9 ± 4 years; range, 3-12 years) obtained as part of their workup for various elbow conditions. We described a technique using distance ratios calculated as a percentage of the patient's own transepicondylar distance, defined as the distance measured between the apices of the medial and lateral epicondyles, on the AP elbow radiograph and the midcoronal MR image. The cross-reference tool on a Picture Archiving and Communication System was then used to identify axial MR image at the level where the transepicondylar distance was measured. On this axial image, a line was drawn connecting the medial and lateral epicondyles (the transepicondylar axis) and its midpoint was determined. The radial nerve angle was measured by a line from the radial nerve to the midpoint of the transepicondylar axis and a line along the lateral half of the transepicondylar axis. On this axial slice, the closest distance from the nerve to the underlying cortex of the distal humerus was measured. To further localize the nerve along the distal humerus, predetermined percentages of the transepicondylar distance were projected proximally from the level of the transepicondylar axis along the longitudinal axis of the humerus on the midcoronal MR image. At these designated heights, the corresponding axial MR image was identified using the cross-reference tool and the nerve was mapped in a similar fashion. We then proposed a simpler method using a best-fit line drawn along the lateral supracondylar ridge on the AP radiograph to define the safe zone for lateral pin entry.

RESULTS

On axial MR images, the radial nerve was located in the anterolateral quadrant with a mean radial nerve angle of 54° (range, 35°-87) at 0% transepicondylar distance (23 MRIs), 41° (range, 24°-63°) at 50% transepicondylar distance (23 MRIs), and ≥ 10° at 75% transepicondylar distance (on the 13 MRIs that extended this far cephalad). The mean closest distance between the radial nerve and the underlying humeral cortex was 10 mm (range, 3-26 mm) at 0% transepicondylar distance and 7 mm (3-16 mm) at 50% transepicondylar distance. On the AP elbow radiograph, the height of the lateral supracondylar ridge, determined by a best-fit line drawn along the lateral cortex of the ridge, diverged from the most proximal extent of the ridge at a point located at 60% transepicondylar distance (range, 51%-76%). At the corresponding location on the axial MR image, the nerve was located anterolaterally with a mean radial nerve angle of 39° (range, 15°-61°) and a mean distance of 6 mm (range, 2-10 mm) from the underlying humerus.

CONCLUSIONS

Our data suggest that percutaneous direct lateral entry Kirschner wires and half-pins can be safely inserted in the distal humerus in children along the transepicondylar axis, either at or slightly posterior to the lateral supracondylar ridge, when placed caudal to the point located where the lateral supracondylar ridge line diverges from the proximal extent of the supracondylar ridge on AP elbow radiograph.

Does motor block related to long-acting brachial plexus block cause patient dissatisfaction after minor wrist and hand surgery? A randomized observer-blinded trial

BACKGROUND

Patient dissatisfaction has been previously associated with motor block in shoulder surgery patients receiving brachial plexus block. For elective minor wrist and hand surgery, we tested whether a regional block accelerating the early return of upper extremity motor function would improve patient satisfaction compared with a long-acting proximal brachial plexus block.

METHODS

A total of 177 patients having elective 'minor' wrist and hand surgery under awake regional block randomly received adrenalized infraclavicular lidocaine 2% 10 ml+ropivacaine 0.75% 20 ml ('long acting', n=90), or adrenalized infraclavicular lidocaine 1.5% 30 ml+long-acting distal median, radial, and ulnar nerve blocks selected according to the anticipated area of postoperative pain ('short acting', n=87). A blinded observer questioned patients on day 1 for numerically rated (0-10) subjective outcomes.

RESULTS

With 95% power, there was no evidence for a 1-point satisfaction shift in the short acting group: satisfaction was similarly high for both groups [median (inter-quartile range)=10 (8-10) vs 10 (8-10), P=0.71], and also demonstrated strong evidence for equivalence [mean difference (95% confidence interval)=-0.18 (-0.70 to 0.35)]. There was no difference between the groups for weakness- or numbness-related dissatisfaction (low for both groups), or for numerically rated or time to first pain. Surgical anaesthesia success was similar between the groups (short acting, 97% vs 93%, P=0.50), although more patients in the short acting group had surgery initiated in ≤25 min (P=0.03).

CONCLUSIONS

Patient satisfaction is not improved after elective minor wrist and hand surgery with a regional block accelerating the early return of motor function. For this surgery, motor block related to a long-acting brachial plexus block does not appear to cause patient dissatisfaction. Clinical Trial Registration number. ACTRN12610000749000, https://www.anzctr.org.au/registry/trial_review.aspx?ID=335931.

Skin temperature measured by infrared thermography after specific ultrasound-guided blocking of the musculocutaneous, radial, ulnar, and median nerves in the upper extremity

BACKGROUND

Sympathetic block causes vasodilatation and increases in skin temperature (T(s)). However, the T(s) response after specific nerve blocking is unknown. In this study, we hypothesized that T(s) would increase after specific blocking of the nerve innervating that area.

METHODS

Forty-six patients undergoing hand surgery were included. We performed ultrasound-guided, specific nerve blocking of either the musculocutaneous, radial, ulnar, or median nerve in each patient and analysed T(s) in the forearm and hand at 2 min intervals in the following 22 min by the use of infrared thermography. Areas of interest corresponding to the cutaneous innervation area of each of the four nerves were defined and the mean T(s) in each area was analysed.

RESULTS

Specific blocking of the ulnar and median nerves caused a substantial increase in mean (sd) T(s) in the areas innervated by these nerves [5.2 (3.2)°C and 5.1 (2.5)°C, respectively; both P<0.0001]. The increase was even larger at the fingertips. Median nerve blocking also increased T(s) in the area of the hand innervated by the radial nerve (P<0.0001). However, T(s) did not increase in any area after either musculocutaneous or radial nerve blocking.

CONCLUSIONS

Specific blocking of the ulnar and median nerve causes substantial increases in T(s) in specific areas of the hand. In contrast, the specific blocking of the musculocutaneous or radial nerve does not increase T(s). Further studies are needed to clarify if these findings can be used to objectively evaluate brachial plexus block success.

Use of ultrasound in detection and treatment of nerve compromise in a case of humeral lengthening

The development of iatrogenic nerve lesions during and following limb lengthening procedures present a challenge to orthopedic surgeons. Early treatment of nerve damage is critical in salvaging full function of the nerve. Precise location of damage, however, must be determined in order to appropriately administer treatment. We report a patient with a short humerus caused by a growth arrest undergoing a 7-cm lengthening who developed a neurapraxic injury of the radial nerve. Nerve compromise was noted 1 month into the lengthening program. Nerve conduction studies and electromyography could not be used to determine the precise site of injury. Likewise, magnetic resonance imaging and computed tomography were contraindicated and inconclusive, respectively, due to the presence of a metallic external fixation device. High-resolution ultrasonography (US) findings, however, correlated with our clinical examination of the patient's radial nerve function and permitted identification of the precise site of nerve involvement. Treatment was administered by removing a causative half-pin. Several days following treatment, nerve function returned to normal. There are a limited number of articles in the literature regarding nerve injuries associated with limb lengthening and their corrective treatments. The outcome of this case underscores the usefulness of US over various other diagnostic techniques under certain circumstances.

Regional anesthesia for acute traumatic injuries in the emergency room

Since the introduction of cocaine in 1884, regional nerve block procedures have been used in anesthesia practice for over 100 years. While almost all medical specialties use simple regional anesthesia techniques, anesthesia providers use a wider variety of more specific nerve block techniques than any other speciality. Anesthesiologists have assumed a vital role in recent military conflicts and, together with surgeons and emergency physicians, have introduced regional anesthesia techniques for the treatment and transport of injured soldiers. While such techniques have only been applied to a limited extent in civilian emergency settings, it is likely that current military experience will enhance future use of regional anesthesia techniques for the care of trauma patients in the civilian prehospital and emergency room settings.

Ultrasound-anatomic correlation of the peripheral nerves of the upper limb

BACKGROUND

Sonography allows good visualization of the peripheral nerves and the vascular and muscular structures that surround them. Our goals are to provide an easy-to-use atlas that gives accurate information about the locations and relations among the nerves in the different parts of the arm and to correlate it with the probe position and the ultrasound images.

MATERIALS AND METHODS

A cadaver right arm was used for the present study. The arterial and venous vessels were injected with red and blue-colored latex to obtain a better correlation with ultrasound slices from two healthy volunteers. The specimen was frozen and then cut into slices with an average thickness of 2 cm, starting from the lower part of the axilla.

RESULTS

Close correlation was present between the ultrasound and anatomic slices identifying the main muscular, vascular and nervous structures. In the arm, median, ulnar and radial nerves were easily seen because of the proximity to vascular landmark and their size. In the forearm, the ulnar nerve was also easy to identify because of the factors previously mentioned; the median nerve was easy to locate between the flexor digitorum superficialis and profundus muscles. The superficial branch of the radial arm was seen in most cases, although some skill was required.

CONCLUSION

Ultrasound is a useful tool to identify the main nerves of the upper arm. This atlas indicates the locations and relations among the nerves, correlating with the ultrasound appearance.

Anatomic relationship of the radial nerve to the elbow joint: clinical implications of safe pin placement

The percutaneous placement of lateral distal humeral pins risks injury to the radial nerve. We aimed to provide a reliable and safe parameter for the insertion of lateral distal humeral pins. A secondary aim of this study was to investigate the effect of pin/screw placement in the intended zone of fixation at the lateral distal humerus. We dissected 70 fresh cadaveric upper limbs and the radial nerve was identified and its course followed into the anterior compartment. The point where the radial nerve crosses humerus in mid lateral plane was identified and the distance between this point and lateral epicondyle was measured, as was the maximum trans-epicondylar distance, along with the olecranon fossa height. Statistical analysis was performed using the Pearson correlation coefficient. The average trans-epicondylar distance was measured at 62 +/- 6 mm (range 52-78 mm), and the average lateral radial nerve height was 102 +/- 10 mm (range 75-129 mm). The ratio of the lateral nerve height to the trans-epicondylar distance was an average of 1.7 +/- 0.2 (range 1.4-2.0). The Pearson correlation coefficient between the lateral nerve height and the trans-epicondylar distance was r = 0.95. A relative dimension, the trans-epicondylar distance is both reliable and easily accessible to the operating surgeon. The absolute safe zone for pin entry into the lateral distal humerus is that area lying within the caudad 70% of a line, equivalent in length to the patient's own trans-epicondylar distance, when projected proximally from the lateral epicondyle.

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.

Upper extremity regional anesthesia: essentials of our current understanding, 2008

Brachial plexus blockade is the cornerstone of the peripheral nerve regional anesthesia practice of most anesthesiologists. As part of the American Society of Regional Anesthesia and Pain Medicine's commitment to providing intensive evidence-based education related to regional anesthesia and analgesia, this article is a complete update of our 2002 comprehensive review of upper extremity anesthesia. The text of the review focuses on (1) pertinent anatomy, (2) approaches to the brachial plexus and techniques that optimize block quality, (4) local anesthetic and adjuvant pharmacology, (5) complications, (6) perioperative issues, and (6) challenges for future research.

Visualization of the course of the sciatic nerve in adult volunteers by ultrasonography

BACKGROUND

The sciatic nerve block by the posterior approaches represents one of the more difficult ultrasound-guided nerve blocks. Our clinical experiences with these blocks indicated a point slightly distal to the subgluteal fold as an advantageous position to allow good ultrasonic visibility. In this study, we systematically scanned the sciatic nerve from the subgluteal fold to the popliteal crease, to determine an optimal point for ultrasonographic visualization.

METHODS

After institutional approval and written informed consent, we recruited 15 volunteers to visualize the sciatic nerve from the subgluteal fold to the popliteal crease using a linear ultrasound probe in the range of 7-13 MHz. The ultrasonographic visibility of the sciatic nerve, nerve diameter (width and thickness), and skin-to-nerve distance at 20 equidistant points between the subgluteal fold and the popliteal crease were recorded.

RESULTS

The sciatic nerve could be successfully visualized in cross-section as a hyperechoic structure on ultrasound in all volunteers. In the course from subgluteal to the popliteal area, the shape of the sciatic nerve changed from flat to round, while the skin-nerve distance varied with the smallest skin-nerve distances at the popliteal crease and at 5.4 cm (on average) distal to the subgluteal fold. The best ultrasonographic visibility scores were found between 7.2 and 10.8 cm (on average) distal to the gluteal fold.

CONCLUSION

Between 5.4 and 10.8 cm from the subgluteal fold seems to be the best area to scan the sciatic nerve in terms of superficial nerve position and good ultrasonic visibility.