MR imaging of the major nerves about the elbow: cadaveric study examining the effect of flexion and extension of the elbow and pronation and supination of the forearm

Muscle interconnections in the anterior and posterior arm compartment: a cadaveric case series with possible clinical implications

PURPOSE

The report describes four cases of accessory bundles (ABs) or fibers connecting the muscles of the anterior with the posterior arm compartment. The ABs morphology (pure muscular or musculofascial or musculoaponeurotic) is described emphasizing their attachment points, characterized as muscles' interconnections.

MATERIALS AND METHODS

Four formalin-embalmed donated male cadavers were dissected.

RESULTS

The muscles' interconnections were unilaterally identified. In the first case, the two ABs originated from the coracobrachialis muscle (CB), received fibers from the biceps brachii (BB), and were inserted into the triceps brachii (TB) medial head. The ABs created an arch over the brachial vessels and the median nerve (MN). In the second case, an accessory musculoaponeurotic structure was identified between CB and TB medial head and extended over the brachial vessels. In the third case, the myofascial ABs between the BB short head and the upper arm fascia, coursed anterior to the MN, the brachial artery, and the ulnar nerve, with direction to the TB medial head. In the fourth case, the three muscular ABs originating from the CB superficial and deep heads, in common with the BB short head, joined the upper arm fascia and the TB medial head and possibly entrapped the musculocutaneous nerve, the MN, and the brachial artery.

CONCLUSION

ABs or musculoaponeurotic extensions may predispose to complications due to their potential compression on nerves and vessels. Clinicians should consider the possible existence of such bridging variants between muscles, in the differential diagnosis of a patient presenting with ischemia, edema, or MN palsy symptoms.

Sonographic normal values for the cross-sectional area of the ulnar nerve: a systematic review and meta-analysis

PURPOSE

Nerve size is a commonly used sonographic parameter when assessing suspected entrapment of the ulnar nerve. We aimed to create a robust set of normal values, based on a critical review of published normal values.

METHODS

We performed a systematic evaluation of studies on normal ulnar nerve sizes, identified in PubMed, Embase, and Cochrane databases. Using meta-analyses, we determined pooled mean cross-sectional area (CSA) values for different anatomical locations of the ulnar nerve throughout the arm. Subgroup analyses were performed for gender, probe frequency, in- or exclusion of diabetic patients, position of the elbow and Asian versus other populations.

RESULTS

We identified 90 studies of which 77 studies were included for further analyses after quality review, resulting in data from 5772 arms of 3472 participants. Subgroup analyses show lower CSA values at at the wrist crease and proximal to the wrist crease when using low frequency probes (< 15 MHz) and at the wrist crease, proximal to the wrist crease, proximal forearm and the distal upper arm in Asians. CSA values were lower when in flexed position compared to extended position for the cubital tunnel inlet only. No difference was found for gender.

CONCLUSIONS

Our systematic review provides a comprehensive set of normal values at sites along the entire length of the ulnar nerve. This provides a foundation for clinical practise and upon which future studies could be more systematically compared.

Systematic Review of Sonographic Measurements of the Ulnar Nerve at the Elbow

A systematic review was performed to identify studies reporting summary data (mean, standard deviation) of sonographic cross-sectional measurements of the ulnar nerve at the elbow. Comparisons of measurements were performed to determine whether statistical differences existed between groups of individuals symptomatic and asymptomatic of ulnar nerve entrapment at the elbow (UNE). Across the four studies meeting the selection criteria of the search, five sample groups were identified and compared: three asymptomatic of UNE and two symptomatic of UNE. There were significant differences between measurements of people with and without UNE ( P < .0001—.041). Significant differences also existed between the two symptomatic populations ( P < .0001—.0062) and between the three asymptomatic populations ( P < .0001—.41). This systematic review demonstrates that significant differences exist between sonographic measurements of ulnar nerve dimension between people with and without UNE, confirming that these measurements are potential discriminators of UNE. The demonstration of significant differences between measurements of ulnar nerve size within sample populations with similar symptomatic status suggests that further studies are required to confirm the effect of ulnar nerve pathologies, measurement protocols, and anthropometric factors.

Preoperative nerve imaging using computed tomography in patients with heterotopic ossification of the elbow

HYPOTHESIS

This study evaluated the usefulness of computed tomography (CT) imaging for preoperative planning of heterotopic ossification (HO) excision, specifically the spatial relationship between HO and radial and median nerves. Our hypotheses were that CT imaging of the elbow can be used (1) to trace the paths of the radial and median nerves, (2) to distinguish the nerves from the heterotopic bone, and (3) to precisely measure distances from the respective nerve to the most clinically relevant HO.

MATERIALS AND METHODS

Patients who had HO removed from the elbow were reviewed retrospectively. On the basis of preoperative CT scans, 22 were identified as likely having HO along the pathway of the radial or median nerve. These cases were independently evaluated by 4 observers, who answered these questions: (1) Can the location of the nerve be adequately seen on sequential images to permit tracing of its path for surgical planning? (2) Can the nerve be distinguished from the HO accurately enough to permit measurement of its distance from the bone? Each observer also measured the shortest distance between nerves and the HO.

RESULTS

Overall utility of the CT images for visualizing the nerves was high. The radial nerve was more readily distinguished from the HO (21 of 22 cases) than the median nerve (17 of 22 cases). The distance measured from HO was less for the radial nerve (3 mm) than for the median nerve (9 mm).

CONCLUSION

This study demonstrates the usefulness of CT imaging to determine the paths of the radial and median nerves and their spatial relationship to HO at the elbow.

Sonographic measurements of the ulnar nerve at the elbow with different degrees of elbow flexion

OBJECTIVE

To determine whether there were differences in the cross-sectional area (CSA) and the flattening ratio of the normative ulnar nerve as it passes between the medial epicondyle and the olecranon at 30° of elbow flexion versus 90° of elbow flexion.

DESIGN

Bilateral upper extremities of normal healthy adult volunteers were evaluated with ultrasound. The CSA and the flattening ratio of the ulnar nerve at the elbow as it passes between the medial epicondyle and the olecranon were measured, with the elbow flexed at 30° and at 90°, by 2 operators with varying ultrasound scanning experience by using ellipse and direct tracing methods. The results from the 2 different angles of elbow flexion were compared for each individual operator. Finally, intraclass correlations for absolute agreement and consistency between the 2 raters were calculated.

SETTING

An outpatient clinic room at a regional rehabilitation center.

PARTICIPANTS

Twenty-five normal healthy adult volunteers.

MAIN OUTCOME MEASUREMENT

The mean CSA and the mean flattening ratio of the ulnar nerve at 30° of elbow flexion and at 90° of elbow flexion.

RESULTS

First, for the ellipse method, the mean CSA of the ulnar nerve at 90° (9.93 mm(2)) was slightly larger than at 30° (9.77 mm(2)) for rater 1. However, for rater 2, the mean CSA of the ulnar nerve at 90° (6.80 mm(2)) was slightly smaller than at 30° (7.08 mm(2)). This was found to be statistically insignificant when using a matched pairs t test and the Wilcoxon signed-rank test, with a significance level of .05. Similarly, the difference between the right side and the left side was not statistically significant. The intraclass correlations for absolute agreement between the 2 raters were not very high due to different measurement locations, but the intraclass correlations for consistency were high. Second, for the direct tracing method, the mean CSA at 90° (7.26 mm(2)) was slightly lower than at 30° (7.48 mm(2)). This was found to be statistically nonsignificant when using the matched pairs t test and the Wilcoxon signed-rank test with a significance level of .05. There was no significant difference in the average flattening ratio between the 2 angles for the left arm (0.54 at 30° vs 0.56 at 90°; P = .619 for the matched pairs t test and .274 for the Wilcoxon signed-rank test). However, for the right arm, the flattening ratio at 90° was significantly higher than that at 30° (0.58 at 90° vs 0.50 at 30°; P = .007 for both the matched pairs t test and the Wilcoxon signed-rank test).

CONCLUSIONS

The mean CSA of the ulnar nerve at the elbow at 30° was not significantly different than at 90°. However, the average flattening ratio at 90° was found to be significantly higher than at 30° for the right arm.

The effect of radial osteotomy on the position of the posterior interosseous nerve

The purpose of this study was to determine whether a radial shaft fracture would decrease the protection provided to the posterior interosseous nerve by the pronation maneuver during posterolateral exploration. The position of the nerve in 14 cadaveric elbows, before and after a radial osteotomy, was determined using CT scans in full supination and full pronation after injection of the nerve with radio-opaque dye. The angle formed by the olecranon, radial head and posterior interosseous nerve, and the distance between the nerve and the most lateral aspect of the radial head were measured.Pronation increased the distance between the lateral radial head and the nerve by a mean of 6.5 mm (range 3.6-10.7). After radial osteotomy, the mean increase was 4.2 mm (range 1.0-8.3), difference 2.3 mm (p = 0.044, 95% CI 0.10 to 3.33). The posterolateral approach requires additional care in the presence of a radial shaft fracture, but pronation is still beneficial.

Lateral epicondylitis and beyond: imaging of lateral elbow pain with clinical-radiologic correlation

The diagnosis of lateral epicondylitis is often straightforward and can be made on the basis of clinical findings. However, radiological assessment is valuable where the clinical picture is less clear or where symptoms are refractory to treatment. Demographics, aspects of clinical history, or certain physical signs may suggest an alternate diagnosis. Knowledge of the typical clinical presentation and imaging findings of lateral epicondylitis, in addition to other potential causes of lateral elbow pain, is necessary. These include entrapment of the posterior interosseous and lateral antebrachial cutaneous nerves, posterolateral rotatory instability, posterolateral plica syndrome, Panner's disease, osteochondritis dissecans of the capitellum, radiocapitellar overload syndrome, occult fractures and chondral-osseous impaction injuries, and radiocapitellar arthritis. Knowledge of these potential masquerades of lateral epicondylitis and their characteristic clinical and imaging features is essential for accurate diagnosis. The goal of this review is to provide an approach to the imaging of lateral elbow pain, discussing the relevant anatomy, various causes, and discriminating factors, which will allow for an accurate diagnosis.

Magnetic resonance imaging of the long bones of the upper extremity

The long bones of the upper extremity are often overlooked in favor of addressing their intervening joints. However, there are a wide variety of pathologic processes that can involve these anatomic segments. To better understand the complex anatomy of the upper extremity, this article is divided into sections describing the osseous, muscular, and neurovascular anatomy of the arm and forearm using a compartmental approach. The discussion touches on a few common normal variants and their potential functional consequences. The upper extremity joints of the shoulder, elbow, and wrist are addressed separately.

Ultrasonography in ulnar neuropathy at the elbow: a critical review

INTRODUCTION

Ultrasonography of the ulnar nerve has been recommended as a useful additional test in ulnar neuropathy at the elbow (UNE).

METHODS

We searched the literature and systemically reviewed all clinical trials in UNE. We also looked for articles about the normal sonoanatomy and specific causes of UNE.

RESULTS

Seven of 14 clinical trials in UNE were suitable for further analysis. Ultrasonographic ulnar nerve size measurement appears to be a test with good diagnostic accuracy. The most frequently reported abnormality was an increased cross-sectional area of the ulnar nerve at the elbow. However, several studies had methodological flaws. In addition, the ultrasonographic techniques and study designs differed among the studies. There were a few other uncontrolled studies about the underlying causes of UNE.

DISCUSSION

The role of ultrasonography in UNE seems promising but could not be firmly established. More prospective studies are needed, and we make several recommendations for further research.

Elbow magnetic resonance imaging variants and pitfalls

Imaging variants of the elbow and pitfalls can be disconcerting and can lead to diagnostic mistakes. Inhomogeneities in the magnetic field and coil position can result in signal changes that may simulate abnormality. Bone signal and morphology variants, such as the islands of red marrow and the pseudodefect of the capitellum and intraarticular inclusions such as plicae, may be mistaken for abnormal findings. Variations of the distal biceps and triceps tendons and different aspects of the ligaments and their insertions, as well as nonpathologic signal and width changes in the ulnar nerve, are other examples of common pitfalls in magnetic resonance imaging of the elbow.

MR imaging findings of anterior interosseous nerve lesions

OBJECTIVE

To study and characterise the MR imaging findings of lesions of the anterior interosseous nerve (AIN).

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) findings of the forearm of ten patients referred to our institution with suspected AIN lesions were retrospectively studied. Five healthy volunteers with normal forearm MRI findings formed a control group. Two musculoskeletal radiologists assessed the forearm musculature for oedema in the distribution of the AIN, median, posterior interosseous and radial nerves on T2-weighted (T2W) fat-saturated sequences. T1-weighted (T1W) images were assessed and graded for the presence of muscle atrophy and fatty involution.

RESULTS

Six patients had undergone surgical exploration; five of these had surgically confirmed AIN compression. Four patients had diagnoses other than AIN compression made on imaging features. Of the cases of proven AIN compression, oedema within the pronator quadratus (PQ) muscle was identified in all cases. PQ atrophy and fatty involution were seen in three (43%) surgically confirmed cases. Cases 2 and 3 also demonstrated oedema in the flexor digitorum profundus (FDP)1 and FDP2 muscles. These cases also showed oedema in the flexor-carpi radialis (FCR) and FDP3/FDP4 muscles, respectively. The four cases of non-AIN compression demonstrated muscle oedema patterns that were atypical for the AIN distribution. They included a rupture of the flexor pollicis longus (FPL) tendon, brachial neuritis, amyotrophic lateral sclerosis and compression of the proximal median nerve.

CONCLUSIONS

MRI is a useful investigation in the diagnostic workup of AIN syndrome. AIN syndrome is likely when there is diffuse oedema of AIN innervated muscles on T2W fat-saturated images. The most reliable sign of an AIN lesion is oedema within the PQ. Oedema in the flexor carpi radialis, FDP3 and FDP4, although not in the classical distribution of the AIN, does not preclude the diagnosis of AIN syndrome.

The clinical applications of peripheral nerve imaging in the upper extremity

Use of different imaging modalities in the diagnosis of peripheral nerve pathology has been growing steadily. This review attempts to summarize their use, particularly with regard to ultrasound and magnetic resonance imaging, and their practical applications in the clinical setting.

The magic angle effect: A source of artifact, determinant of image contrast, and technique for imaging

This review provides a formalism for understanding magic angle effects in clinical studies. It involves consideration of the fiber-to-field angle for linear structures such as tendons, ligaments, and peripheral nerves, disc-like and circular structures such as menisci and labra, as well as complex three-dimensional structures. There may be one or more fiber types with different orientations within each of these tissues. The orientation of these fibers to B(0) is crucial in determining their magic angle effect. Tissues may show a variety of appearances depending on their baseline T2, as well as the increase in T2 produced by the magic angle effect. The appearances are affected by TE, which affects both the general tissue signal level and the change in signal produced by the magic angle effect, fiber-to-slice orientation, and partial volume effects. Deliberate positioning of structures and tissues at particular orientations to B(0) can be used to increase the signal from tissues such as tendons and ligaments and so allow them to be imaged with conventional sequences. The technique can also be used to produce contrast between tissues with fibers that have different orientations to B(0).

Normal MR imaging anatomy of the elbow

The functional complexity achieved at the elbow is a reflection of the sophisticated architecture that embodies this articulation. In addition to challenging anatomic relationships to conceptualize, there are many anatomic variations that exist in the osseous, capsular, and muscular structures. This article offers a detailed description of the structural and imaging anatomy of the elbow, information that establishes the foundation of imaging interpretation of internal derangements.

Magnetic resonance imaging of the elbow. Part II: Abnormalities of the ligaments, tendons, and nerves

Part II of this comprehensive review on magnetic resonance imaging of the elbow discusses the role of magnetic resonance imaging in evaluating patients with abnormalities of the ligaments, tendons, and nerves of the elbow. Magnetic resonance imaging can yield high-quality multiplanar images which are useful in evaluating the soft tissue structures of the elbow. Magnetic resonance imaging can detect tears of the ulnar collateral ligament and lateral collateral ligament of the elbow with high sensitivity and specificity. Magnetic resonance imaging can determine the extent of tendon pathology in patients with medial epicondylitis and lateral epicondylitis. Magnetic resonance imaging can detect tears of the biceps tendon and triceps tendon and can distinguishing between partial and complete tendon rupture. Magnetic resonance imaging is also helpful in evaluating patients with nerve disorders at the elbow.

Normal MR imaging anatomy of the elbow

The functional complexity achieved at the elbow is a reflection of the sophisticated architecture that embodies this articulation. In addition to challenging anatomic relationships to conceptualize, there are many anatomic variations that exist in the osseous, capsular, and muscular structures. This article offers a detailed description of the structural and imaging anatomy of the elbow, information that establishes the foundation of imaging interpretation of internal derangements.

Nerves in a pinch: imaging of nerve compression syndromes

Nerve compression is a common entity that can result in considerable disability. Early diagnosis is important to institute prompt treatment and to minimize potential injury. Although the appropriate diagnosis is often determined by clinical examination, the diagnosis may be more difficult when the presentation is atypical, or when anatomic and technical limitations intervene. In these instances, imaging can have an important role in helping to define the site and etiology of nerve compression or in establishing an alternative diagnosis. MR imaging and ultrasound provide direct visualization of the nerve and surrounding abnormalities. For both modalities, the use of high-resolution techniques is important. Bony abnormalities contributing to nerve compression are best assessed by radiographs or CT. For the radiologist, knowledge of the anatomy of the fibro-osseous tunnels, familiarity with the causes of nerve compression, and an understanding of specialized imaging techniques are important for successful diagnosis of nerve compression.

Magnetic resonance imaging of sports injuries of the elbow

Many abnormalities seen in the elbow result from trauma, often from sports such as baseball and tennis. Elbow problems are frequently related to the medial tension-lateral compression phenomenon, where repeated valgus stress produces flexor-pronator strain, ulnar collateral ligament sprain, ulnar traction spurring, and ulnar neuropathy. Lateral compression causes osteochondral lesions of the capitellum and radial head, degenerative arthritis, and loose bodies. Other elbow abnormalities seen on magnetic resonance imaging include radial collateral ligament injuries, biceps and triceps tendon injuries, other nerve entrapment syndromes, loose bodies, osseous and soft-tissue trauma, arthritis, and masses, including bursae.

Magnetic resonance imaging of the upper extremity: advances in technique and application

Vast advances in technology have taken place in the field of radiology led by the introduction of magnetic resonance imaging. The added advantages of exquisite soft tissue contrast and multiplanar imaging capabilities have revolutionized the understanding of complex anatomic relationships and diagnoses. The current authors will focus on the introduction of new advances in magnetic resonance imaging of the upper extremity that may prove helpful in the diagnosis and treatment of upper extremity abnormalities.