MR Imaging of the Elbow




Almost all movements of the upper extremities during routine daily life and many athletic activities require a painless and stable elbow joint. Studying the elbow is a diagnostic challenge because of its complex anatomy. MR imaging is an extremely important tool in the evaluation of common elbow disorders, the spectrum of which ranges from obvious acute lesions to chronic overuse injuries whose imaging manifestations can be subtle.


Key points








  • The elbow is a complex anatomic region difficult to assess even by experienced examiners.



  • Precise imaging diagnosis helps the management of acute lesions and chronic overuse injuries of the elbow.



  • MR imaging is of great importance for patients on the way to regaining a normal elbow joint that permits a functional range of painless motion.






Imaging protocols


MR images are acquired using T1-weighted and T2-weighted and proton density (PD) images, with and without fat suppression. Current protocols differ between specialists, according to their preferences. MR imaging of the elbow is directly dependent on the use of surface coils specialized for the imaging of extremities; moreover, the field of view should be limited to the minimal area necessary to encompass all anatomic structures.


The elbow must be placed close to or at the scanner’s isocenter to provide the field homogeneity required for off-center fat suppression. Typically, patients are placed in a supine position with their arm to the side, or in a lateral decubitus position with their back leaning against the scanner. The patient also can be positioned prone with their arm extended overhead (the Superman position), a position that, albeit less well tolerated and more prone to introducing motion degradation artifacts, can be useful with larger patients. In certain situations, such as with biceps insertion pathology, the tendon can be imaged better with the elbow flexed, the shoulder abducted, and the forearm supinated: the so-called FABS (flexed abducted supinated) position.




Imaging protocols


MR images are acquired using T1-weighted and T2-weighted and proton density (PD) images, with and without fat suppression. Current protocols differ between specialists, according to their preferences. MR imaging of the elbow is directly dependent on the use of surface coils specialized for the imaging of extremities; moreover, the field of view should be limited to the minimal area necessary to encompass all anatomic structures.


The elbow must be placed close to or at the scanner’s isocenter to provide the field homogeneity required for off-center fat suppression. Typically, patients are placed in a supine position with their arm to the side, or in a lateral decubitus position with their back leaning against the scanner. The patient also can be positioned prone with their arm extended overhead (the Superman position), a position that, albeit less well tolerated and more prone to introducing motion degradation artifacts, can be useful with larger patients. In certain situations, such as with biceps insertion pathology, the tendon can be imaged better with the elbow flexed, the shoulder abducted, and the forearm supinated: the so-called FABS (flexed abducted supinated) position.




Anatomy


The elbow is a complex joint formed by 3 distinct articulations: the ulnohumeral, radiohumeral, and radioulnar articulations. The first 2 articulations function as a hinge, permitting flexion and extension between the arm and forearm; the last 2 accomplish the pivot motion of pronation and supination and are functionally linked to the distal radioulnar joint and the wrist. These joints have a common articular cavity and share a multitude of enveloping structures, including the synovium, capsule, and ligaments, all of which render the elbow a single anatomic unit.


The osseous anatomy of 3 bones: the humerus, radius, and ulna; and, although examining the elbow can appear deceptively simple, knowledge of a few potential MR imaging pitfalls ( Box 1 ) can greatly reduce the risk of misdiagnoses, including osteochondral defects ( Figs. 1 and 2 ).



Box 1





  • Pseudodefect of the capitellum



  • Pseudolesion of the trochlear notch



  • The anterior bundle of the UCL and the LUCL frequently have striated appearance



  • Bifid DBT



  • Anconeus epitrochlearis



  • Ulnar nerve high signal intensity on fluid-sensitive sequences



  • Plicae size less than 3 mm



Anatomic variants that must be recognized and distinguished from pathologic abnormality



Fig. 1


Anatomic variants to be recognized and distinguished from pathologic abnormality. Sagittal T2-weighted images showing ( A ) pseudodefect of the capitellum ( arrow ); ( B ) pseudolesion of the trochlear notch ( arrow ).



Fig. 2


Anatomic variants to be recognized and distinguished from pathologic abnormality. ( A ) Coronal T1-weighted image shows the typical striated appearence of the UCL ( arrow ). ( B ) Sagittal T2-weighted image demonstrates an anconeus epitrochlearis muscle ( arrow ). ( C ) Axial short tau inversion recovery (STIR) shows the normal appearence of the ulnar nerve at the elbow ( arrow ). ( D ) Axial proton density-weighted image of a bifid DBT ( arrow ).


The capsule of the elbow is reinforced by strong collateral ligaments, but is relatively weak and loose anteriorly and posteriorly, permitting a large range of flexion through extension. The ulnar collateral ligament (UCL) consists of 3 ligamentous bundles ( Fig. 3 , Table 1 ). The anterior bundle is the major medial stabilizer of the elbow and, fortunately, is the easiest to image (see Box 1 , Figs. 2 and 7 ). It arises from the medial epicondyle and attaches to the coronoid process (sublime tubercle). This bundle itself has functional anterior and posterior components, with the former component more important in extension and the latter more important in flexion; however, they are not seen as separate structures. The posterior bundle extends from below the medial epicondyle to the medial olecranon, forming the floor of the cubital tunnel. It becomes a secondary stabilizer of the elbow when the joint is flexed beyond 90°. The transverse bundle consists of fibers that extend from the anterior and posterior bundles and does not contribute to elbow stability.




Fig. 3


Normal UCL. ( A ) Coronal T1-weighted image of the anterior bundle ( arrow ). ( B ) Axial PD-weighted image of the posterior bundle ( arrow ).


Table 1

Ulnar collateral ligament
























Bundle Location Function View
Anterior From epicondyle to coronoid process Major medial stabilizer Coronal
Posterior Cubital tunnel floor Secondary stabilizer Axial
Transverse Between anterior and posterior bundles No contribution to stability


The radial collateral ligament (RCL) is a complex structure ( Fig. 4 , Table 2 ). The annular ligament is the primary stabilizer of the proximal radioulnar joint (PRUJ) and is best seen on axial images wrapping around the side of the radial head from one side of the radial notch to the other. The RCL arises from the anterior margin of the lateral epicondyle, inserts onto the annular ligament and fascia of the supinator muscle, and is best seen on coronal images. The lateral ulnar collateral ligament (LUCL) is the major posterolateral stabilizer and can be seen on coronal or sagittal images, arising more posteriorly and superficially from the lateral epicondyle, and inserting onto the supinator crest.




Fig. 4


Normal RCL complex. ( A ) Axial T1-weighted image of the annular ligament ( arrows ). ( B ) Coronal T1-weighted image of the RCL ( arrow ). ( C ) Coronal T1-weighted image of the LUCL ( arrow ).


Table 2

Radial collateral ligament
























Ligament Location Function View
Annular Around radial head Primary stabilizer PRUJ Axial
Sagittal
Radial From epicondyle to annular ligament Annular ligament stabilizer Coronal
Lateral ulnar From epicondyle to supinator crest Major posterolateral stabilizer Coronal
Sagittal


Numerous muscles originate at or insert into the osseous surfaces of the elbow. They can be divided into anterior, posterior, medial, and lateral compartments ( Table 3 ).



Table 3

Muscles compartments of the elbow



















Compartment Muscles
Lateral Extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum communis, extensor carpi ulnaris, extensor digiti minimi, anconeus, supinator
Medial Pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, brachioradialis
Anterior Brachialis, biceps
Posterior Triceps

Adapted from Walz DM, Newman JS, Konin GP, et al. Epicondylitis: pathogenesis, imaging, and treatment. Radiographics 2010;30:169, 177.


The distal biceps tendon (DBT) consists of 2 unique anatomic and functional subunits, even though it usually is seen, on imaging, inserting as a single, flat paratenon-lined extrasynovial structure with no tendon sheath ( Fig. 5 ). The superficial fibers of the biceps tendon form a broad aponeurotic sheet, termed the lacertus fibrosus (LF), which sweeps across the antecubital fossa, covering and protecting the median nerve and brachial artery. It also blends with the antebrachial fascia that covers the superficial forearm flexors, thereby assisting with forearm supination and elbow flexion. An intact LF can also prevent retraction of a ruptured biceps tendon, facilitating repair of chronic ruptures.




Fig. 5


DBT appears as a single unit ( A ), although it should be thought of as having 2 heads ( B ). As the tendon approaches the radial tuberosity, it gradually externally rotates 90°, causing the short head (SH, arrow ) to insert distal to the long head (LH, arrow ). The SH plays a greater role in flexion of the elbow; meanwhile, the LH acts as a powerful supinator.


The triceps is the only major extensor of the elbow. It is a tripinnate muscle composed of long, lateral, and medial heads. As a result of this laminar anatomy, each component may be injured separately. It primarily inserts onto the olecranon and posterior joint capsule.


The 3 major nerves in the elbow are the radial, median, and ulnar nerve. The ulnar nerve is the most frequently injured because it is relatively exposed while coursing through the cubital tunnel; however, ulnar neuropathy may also arise from nontraumatic causes (see Box 1 , Fig. 2 ).


The bursae about the elbow joint include the olecranon, bicipitoradial, and interosseous bursae. Bursitis can arise from different causes, with the olecranon bursa the most commonly affected ( Fig. 6 ). Several synovial plicae have been described, with the posterolateral plicae being the most frequently identified (see Box 1 , Fig. 6 ).




Fig. 6


( A ) Axial STIR shows an olecranon chronic bursitis demonstrated by a mild thickening of the synovial membrane ( arrow ) and heterogeneous signal ( asterisk ). ( B ) Sagittal STIR shows a bicipitoradial acute bursitis visible as a fluid collection with thin walls ( arrow ). ( C ) Sagittal T2-weighted image shows enlarged posterolateral plicae with high signal intensity ( arrow ).




Elbow instability


The elbow is one of the most stable articulations in the human skeleton. Because the forces that cross the elbow joint are principally valgus in nature, the joint is not often subjected to varus stress, nor does its articular anatomy predispose it to true varus instability ( Box 2 ).



Box 2




  • 1.

    The most important static soft tissue constraints are the LUCL and the anterior bundle of the UCL.


  • 2.

    Caution should be exercised when making the diagnosis of partial UCL detachment: remember the striated appearance of the ligament.


  • 3.

    UCL midsubstance disruptions account for most traumatic injuries.


  • 4.

    Conventional MR imaging shows sensitivity, specificity, and accuracy that approach 100% for full-thickness UCL tears.


  • 5.

    The anterior bundle of the UCL is often intact even when the radial head and coronoid process are both fractured.


  • 6.

    Posttraumatic laxity, disruption, or avulsion of the LUCL is considered to be the main contributing factor in PLRI.


  • 7.

    The most common injury to the LUCL is soft tissue avulsion at the proximal humeral attachment, often with concomitant injury to the common origin of the RCL.


  • 8.

    Elbow dislocation is most commonly associated with a torn capsule, but the capsule may be intact if the coronoid process is fractured.


  • 9.

    An abnormal posterolateral plicae usually reflects incompetence of the UCL.


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Sep 18, 2017 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on MR Imaging of the Elbow

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