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Musculoskeletal ultrasound of the elbow

Musculoskeletal ultrasound of the elbow
Author:
David J Berkoff, MD, FAAEM, CAQSM
Section Editor:
Karl B Fields, MD
Deputy Editor:
Jonathan Grayzel, MD, FAAEM
Literature review current through: Dec 2022. | This topic last updated: Dec 09, 2022.

INTRODUCTION — The elbow is susceptible to a variety of injuries and conditions. Due to the relatively superficial location of a majority of the elbow structures, many of these pathologic conditions can be assessed using ultrasound (US).

This topic will review a standard, systematic approach to musculoskeletal ultrasonography of the elbow. Topics devoted to conditions and injuries involving the elbow and upper extremity are found separately:

General evaluation (See "Evaluation of elbow pain in adults" and "Elbow injuries in active children or skeletally immature adolescents: Approach".)

Adult injuries and conditions (See "Elbow tendinopathy (tennis and golf elbow)" and "Ulnar neuropathy at the elbow and wrist" and "Radial head and neck fractures in adults".)

Pediatric injuries and conditions (See "Evaluation and management of condylar elbow fractures in children" and "Epicondylar and transphyseal elbow fractures in children" and "Supracondylar fractures in children".)

USES, ADVANTAGES, AND LIMITATIONS OF ELBOW, WRIST, AND HAND ULTRASOUND — Musculoskeletal ultrasound (US) uses high frequency sound waves (1 to 20 megahertz, MHz) to produce high-resolution images of soft-tissue structures (eg, nerves, tendons, muscles, ligaments, bursae) and bony surfaces.

US has many advantages over other imaging modalities, including portability and rapid diagnosis [1]. Many of these general advantages are discussed separately. Specifically for the elbow, advantages include dynamic imaging of the ulnar collateral ligament medially and the ulnar nerve at the cubital tunnel; visualization of soft tissue abnormalities, including tendon tears and the typical changes associated with tendinopathy; ligament and muscle injury; bony injury; and identification of an elbow joint effusion [2-6]. (See "Musculoskeletal ultrasound of the shoulder", section on 'Uses, advantages, and limitations of shoulder ultrasound'.)

ELBOW ANATOMY FOR ULTRASOUND EVALUATION — A general discussion of the clinical anatomy of the elbow is provided separately. (See "Evaluation of elbow pain in adults", section on 'Clinical anatomy'.)

The elbow is comprised of three bones, the humerus, radius, and ulna (figure 1). The ulnohumeral joint is primarily responsible for flexion and extension, while the radiocapitellar joint enables pronation and supination. The tip of the olecranon inserts into the olecranon fossa on the humerus when the elbow is in extension (figure 2).

For the purposes of sonographic evaluation, the elbow is divided into four anatomic quadrants: anterior, lateral, posterior, and medial. The structures assessed during the ultrasound examination include those listed below [2-5].

Anterior ‒ Structures evaluated in the anterior elbow include: brachialis and brachioradialis muscles, distal biceps tendon (figure 3), radial (figure 4 and figure 5) and median nerves (figure 6), brachial artery (figure 7), and anterior joint capsule.

Medial ‒ Structures evaluated in the medial elbow include: common wrist flexor tendon (figure 8 and figure 9 and figure 10) and ulnar collateral ligament (figure 11 and figure 12).

Posterior ‒ Structures evaluated in the posterior elbow include: posterior elbow joint, triceps tendon insertion, cubital tunnel, and ulnar nerve (figure 13 and figure 10).

Lateral ‒ Structures evaluated in the lateral elbow include: common wrist extensor tendon (figure 14 and figure 15), radiocapitellar joint, and radial head (figure 1).

ULTRASOUND EXAMINATION OF THE ELBOW — A systematic approach to imaging the elbow is best. The standard approach divides the joint into four quadrants: anterior, medial, posterior, and lateral. Within each of these areas, particular structures are readily identified and evaluated.

Anterior elbow — Begin the musculoskeletal ultrasound examination of the elbow by having the patient fully extend the affected elbow with the palm facing up. The transducer is oriented in line with the axis of the humerus to obtain longitudinal images of the structures crossing the anterior elbow (picture 1). Using this view, the radiocapitellar and humeroulnar joints, coronoid fossa, and anterior fat pad are seen (image 1).

Next, the transducer is rotated 90 degrees to obtain a transverse image of the anterior elbow (picture 2). Moving the transducer caudally, the transition from biceps muscle to tendon is seen, as well as the brachialis and brachioradialis muscles as they pass anterior to the elbow joint. The brachialis muscle originates at the lower half of the anterior aspect of the humerus and inserts on the tuberosity of the ulna. The brachioradialis muscle originates on the lateral supracondylar ridge and passes distal to the styloid process of the radius. Medial and superficial to the brachialis muscle lies the brachial artery, and medial to the artery is the median nerve. The brachioradialis sits lateral to the brachialis and both lie just anterior to the joint line (image 2).

As the transducer is moved further distally, the biceps tendon comes into view as it inserts onto the tuberosity of the proximal radius (radial tuberosity). Despite its superficial location, the distal biceps tendon can be difficult to image clearly. A number of techniques are used to visualize the tendon insertion. The most common method begins by having the patient fully extend their elbow and maximally supinate their forearm. The transducer is oriented in the long axis of the tendon (picture 3)and the sonographer scans along the tendon distally towards its insertion on the radial tuberosity (image 3). Note that as the tendon travels distally to its insertion, it moves deeper and laterally. To maintain a satisfactory image of the tendon as it approaches its insertion, the sonographer needs to tilt (or "toe down") the transducer as the tendon moves to keep the transducer perpendicular to the tendon. If this is not done, the resulting anisotropy can obscure the images.

Two alternative techniques for visualizing the distal biceps tendon have been described. The first is commonly referred to as the "snake charmer." To perform this technique, the patient fully flexes their elbow and maximally pronates their forearm. The transducer is held in short axis relative to the forearm (picture 4), and placed approximately 4 to 5 cm distal to the olecranon. The distal biceps tendon insertion is seen wrapping around the radius in its long axis (image 4 and movie 1). Using this technique, only the distal aspect of the tendon insertion is visible, but this is typically a good starting place to determine whether the tendon is intact distally.

The second alternative technique uses the common flexor bundle as a window to visualize the tendon insertion. To perform this technique, the patient fully supinates their forearm and keeps their elbow flexed at 90 degrees, bringing the distal biceps tendon nearly perpendicular to the radius. The transducer is then positioned in long axis relative to the biceps tendon. Scanning is performed from posterior to anterior relative to the humerus. The distal biceps tendon lies adjacent to (and travelling in same direction as) the brachial artery and vein (image 5).

Next, the radial nerve is examined. The transducer is placed proximal and anterolateral to the elbow and oriented in a transverse plane to the joint. The nerve is seen initially between the brachialis (deep) and brachioradialis (superficial) muscles. The nerve divides at the level of the joint and the posterior interosseous nerve (PIN) can be seen passing over the radial head and into the radial tunnel within the arcade de Frohse. This part of the examination is performed with the transducer held in a transverse orientation relative to the nerve. The clinician glides the probe distally, which brings the PIN into view, which can then be followed diving deep between the heads of the supinator, adjacent to the radial neck (image 6 and movie 2).

Lateral elbow — As the transducer is moved laterally, the origin of the common extensor tendon at the lateral epicondyle comes into view. The common extensor tendon is the common origin of the extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles at the lateral epicondyle.

To perform this part of the examination, the patient rests their elbow on a table with the elbow flexed to 90 degrees. The proximal edge of the transducer is placed directly on the bony lateral epicondyle and aligned in a long axis orientation to the muscle (picture 5). The common extensor tendon lies superficial to the radiocapitellar joint and attaches to the lateral epicondyle. With this view, the confluence of the muscle fibers as they form the common extensor tendon, which inserts onto the bony epicondyle, can be appreciated (image 7).

By turning the transducer 90 degrees to the transverse plane, the common extensor tendon becomes visible in its short axis at its origin on the bony lateral epicondyle. As the transducer is moved distally, we see the transition from tendon to muscle. Deep to the tendon lies the radiocapitellar joint, with the radial collateral ligament crossing superficially. The radial collateral ligament merges with the annular ligament and as a bundle they extend from the lateral epicondyle to the radial head and the ulna. In this view, the ligament complex and radial head are seen. Dynamic evaluation of the radiocapitellar joint may reveal fluid within the joint and radiocapitellar instability. Bony injury and irregularities of the proximal radius and radial head may also be seen.

Posterior elbow — To perform the examination of the posterior elbow, the seated patient places their hand on a bed or table with the elbow flexed to approximately 90 degrees (picture 6). Using a long axis view and looking from proximal to distal, the transition of triceps muscle to tendon can be appreciated. The triceps muscle has three heads that merge into a single tendon that inserts posteriorly onto the olecranon process. Deep to the triceps tendon is the olecranon fossa and olecranon recess. By having the patient slowly move their elbow from flexion into extension while scanning (dynamic imaging), any fluid filling this posterior recess can be identified. More superficially, any fluid present within the olecranon bursa can also be visualized.

As the transducer is moved posteromedially, the cubital tunnel comes into view. The cubital tunnel is seen best when the patient is positioned with their hand on a table and their elbow flexed to about 30 degrees. The transducer is placed in a transverse orientation relative to the nerve. The ulnar nerve is seen in its short axis as it passes through the tunnel lying against the medial wall adjacent to the ulna (image 8 and movie 3). The triceps tendon lies lateral to the nerve.

As the transducer is moved distally, the two heads of the flexor carpi ulnaris muscle can be seen on either side of the ulnar nerve. The ulnar nerve can be imaged dynamically to assess for instability. To do so, the examiner must maintain very light pressure on the transducer to avoid inadvertently holding the nerve within the groove. With the transducer held in the transverse plane, the patient's elbow is passively flexed and extended. An unstable nerve will be seen subluxing or dislocating from its normal location within the groove, moving away from the medial head of the triceps, and ending up on the medial side of the medial epicondyle.

Medial elbow — To perform the examination of the medial elbow, the patient's elbow may rest on the examination table with the shoulder externally rotated and elbow slightly flexed. The transducer is placed over the bony medial epicondyle and oriented in the long axis of the common flexor tendon, which attaches to the epicondyle (image 9). The common flexor tendon is the origin for the pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, and flexor carpi ulnaris muscles. The common flexor tendon is superficial, and shorter than the common extensor tendon, and more of the musculotendinous transition is visible with ultrasound. Deep to the tendon lies the ulnar collateral ligament (UCL) (image 10). The UCL arises from the posterior distal aspect of the medial epicondyle and inserts onto the coronoid process. The UCL is comprised of three bands, of which the anterior band inserts onto the sublime tubercle of the ulna.

For optimal imaging, when evaluating the common flexor tendon the distal tip of the transducer should point towards the palmaris longus tendon at the wrist. When evaluating the UCL the distal portion of the transducer should be rotated slightly so it points towards the little finger. In addition, the elbow may be flexed further when imaging the UCL, approaching 90 degrees.

Dynamic scanning can be used to assess the integrity of the UCL. To do so, the transducer is oriented in the long axis of the ligament. The sonographer then applies a valgus stress to the elbow while watching for widening of the joint space (movie 4).

SONOGRAPHIC PITFALLS AND APPEARANCE OF ELBOW PATHOLOGY — Although most structures surrounding the elbow are superficial, it is important to recognize the difference between pathology and artifact. When imaging tendons, beware of anisotropy. Unless an abnormality is seen on more than one orthogonal view, be cautious of calling it pathologic. When visualizing nerves, particularly the ulnar nerve in the cubital tunnel, use dynamic US to assist the evaluation. Although the nerve may appear normal when stationary, a dynamic evaluation may reveal instability.

Common pathology that may be seen during a musculoskeletal US examination of the elbow includes the following:

Common extensor tendinosis with spur (image 11)

Ulnar collateral ligament tear (image 12)

Medial epicondylosis (image 13)

Distal biceps tendon tear (image 14)

Triceps insertion injury

Ulnar nerve pathology

ADDITIONAL ULTRASOUND RESOURCES — Instructional videos demonstrating proper performance of the ultrasound examination of the elbow and related pathology can be found at the website of the American Medical Society for Sports Medicine: anterior elbow ultrasound, lateral elbow ultrasound, posterior elbow ultrasound, and medial elbow ultrasound. Registration must be completed to access these videos, but no fee is required.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Musculoskeletal ultrasound".)

SUMMARY AND RECOMMENDATIONS

Uses of wrist ultrasound examination – The elbow is susceptible to a variety of injuries and conditions. Due to the relatively superficial location of a majority of the elbow structures, many of these pathologic conditions can be assessed using ultrasound (US). Specifically for the elbow, the advantages of US evaluation include dynamic imaging of the ulnar collateral ligament medially and the ulnar nerve at the cubital tunnel; visualization of soft tissue abnormalities, including tendon tears and the typical changes associated with tendinopathy; and identification of an elbow joint effusion. (See 'Uses, advantages, and limitations of elbow, wrist, and hand ultrasound' above.)

Anatomy – An understanding of elbow anatomy is essential for interpreting US images. A few salient details and images pertaining to elbow anatomy are provided above, while a more detailed discussion of the clinical anatomy of the elbow is provided separately. (See 'Elbow anatomy for ultrasound evaluation' above and "Evaluation of elbow pain in adults", section on 'Clinical anatomy'.)

Examination performance – US of the elbow is relatively straightforward due to the superficial location of most of the structures of interest. A systematic approach to imaging the elbow is best. The standard approach divides the joint into four quadrants: anterior, medial, posterior, and lateral. Within each of these areas, particular structures are readily identified and evaluated. Performance of the US examination for each quadrant is described in the text. (See 'Ultrasound examination of the elbow' above.)

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