Elbow and Forearm

Thomas H. Berquist

Laura W. Bancroft

Magnetic resonance imaging (MRI) of the elbow and forearm can clearly define normal bone and soft tissue anatomy and pathology.¹^,²^,³^,⁴^,⁵^,⁶^,⁷^,⁸ Clinical information (symptomatic region, the relationship of symptoms to flexion, extension, pronation, and supination) and the type of pathology suspected are important in planning MRI examinations. To solve a given clinical problem, the patient must be comfortable, properly positioned, and the best image planes and pulse sequences selected to optimize lesion identification and characterization of lesions.

TECHNIQUE

Patient Positioning and Coil Selection

Patient positioning is as important with MRI as with other radiographic techniques (see Chapter 3). The types of coils available, gantry limitations, patient size, and clinical status may lead to suboptimal examinations, particularly in the upper extremity. The confining nature of the most high field strength MR gantries, excluding open and extremity systems, reduces positioning options, especially for larger patients.¹^,²^,³^,⁴^,⁵^,⁶^,⁷ Imaging can be accomplished with lower field strength open or extremity units. We currently use both 1.5 and 3.0Tunits for elbow examinations.² Patients are usually most comfortable when supine with the elbow extended, forearm supinated, and arm at their side (Fig. 10.1). The contralateral arm can be placed above the head to improve centering of the elbow to be examined.² When the elbow being examined is above the head (Fig. 10.1B and C), patient discomfort becomes an issue. A dedicated circumferential elbow coil can be used in this position (Fig. 10.2A). The larger phased array coil is preferred for examination of larger areas such as the forearm or forearm and elbow (Fig. 10.2B).

Different positions and coils may be required with larger patients.²^,³^,⁵^,⁶ With larger patients, the elbow may have to be positioned with the arm above the head and the elbow extended as much as possible (Superman position) and the patient in a rotated or prone position (Fig. 10.1).¹^,²^,³^,⁵ In this setting, the prone position with the arm above the head is most often selected.¹^,⁹^,¹⁰^,¹¹ Unfortunately, patient discomfort can be significant when the arm is above the head. As a result, images may be degraded by motion artifact. In our initial review of 200 upper extremity cases, we found image degradation due to motion in 25%.Motion artifact is usually not a problem when the patient is supine with the arm at the side.¹^,² These positioning approaches can be used with children and adults.

The site of pain or suspected pathology can be marked with a vitamin E capsule. However, care should be taken not to compress or distort the underlying soft tissues. Marking the symptomatic site is particularly useful when the study is normal.³ Oral sedation may be required in children under 5 years of age (see Chapter 3).¹²

In certain situations, such as biceps insertion pathology, positioning the patient with the elbow flexed or appropriately rotated displays anatomy to better advantage (Fig. 10.3). This may be impossible with large patients. Smaller patients can be rotated into the oblique position with the elbow flexed at the side. Axial examinations during
pronation and supination are also useful for evaluating the biceps tendon and subtle abnormalities in the radioulnar joint. Both axial and sagittal images should be obtained. When motion studies are required, we have used gradient echo (GRE) sequences (see below) and cine studies. Quick et al.¹³ used fast imaging steady state precession (FISP) sequence to perform motion studies of the elbow and other joints. True FISP is a steady state precession GRE sequence. The parameters used in this study include repetition time/echo time (TR/TE) of 2.2/1.1 ms, flip angle (FA) 50°, field of view (FOV) 12 to 27 cm, section thickness of 6 mm, and a 256 × 135 matrix.¹³

Figure 10.1 Illustration of positions for imaging the elbow. Positioning the arm (A) at the side is most comfortable for the patient. When the arm is positioned (B, C) above the head, the patients have more difficulty tolerating the examination. The patient is rotated in B, which is often necessary with larger patients or when elbow flexion is needed to evaluate the biceps tendon.

Giuffre and Moss¹⁴ used the flexed abducted supinated position to evaluate the biceps tendon. The elbow is flexed with the arm above the head and the forearm positioned with the thumb up (Fig. 10.4). This approach improves the ability to include the entire biceps tendon in the image plane enhancing the ability to differentiate partial from complete tears and other subtle pathology. This position may be difficult to maintain, resulting in motion artifact.¹^,²

Figure 10.2 Photographs of the elbow (A) and larger phased-array (B) coils.

Comparison of both extremities is useful in patients with subtle pathology. This doubles the examination time with conventional coils. Dual coils allow simultaneous examinations of both upper extremities. This will reduce image time significantly without reduction in image quality.¹⁵^,¹⁶^,¹⁷

Yoshioka et al.¹⁸ used microscopic coils to evaluate the elbow. Their work is preliminary. Conventional pulse sequences, FOV of 5 to 7 cm, image matrix of 140 to 224 × 512, 2 to 6 acquisitions, and a 14 × 17 cm flex coil with a 23 mm microscopic coil were used together to evaluate
the elbow. Signal to noise ratios and spatial resolution were improved compared to conventional coil techniques.¹⁸

Figure 10.3 Normal distal biceps tendon. A: Sagittal 1.5-T T1-weighted image with the elbow flexed demonstrates the biceps tendon as it expands (arrowheads) near its attachment on the tuberosity of the radius. B: Properly rotated 3.0-T turbo spin-echo fat-suppressed T2-weighted image clearly demonstrates the biceps tendon (arrows) to the level of the radial tuberosity.

Other general parameters for elbow imaging include a small FOV (10 to12 cm); 256 × 192, 256 × 256, 512 × 512 matrixes; and 1 to 2 acquisitions. Section thickness varies with the area of interest and volume of tissue, but it is typically 4 mm or less in the elbow (Table 10.1). A larger FOV is required to examine the forearm or the elbow and forearm together.

Figure 10.4 Illustration of the flexed abducted supinated view for evaluation of the biceps tendon. The thumb is up.

Pulse Sequences and Image Planes

Image planes for the elbow and forearm include axial, sagittal, coronal, oblique, and reformatting of thin-section GRE images.¹^,²^,³^,⁵^,¹⁹^,²⁰ The axial image plane is useful for neurovascular, tendon, annular ligament, ulnar collateral ligament, lateral collateral ligament, and muscle anatomy. The sagittal plane is useful as a second plane for biceps and triceps tears or to define the extent of a lesion identified on axial images. Sagittal images are also useful for evaluation of articular cartilage, loose bodies, and synovits. The coronal plane is useful for evaluating the articular surfaces and the collateral ligaments.²^,³^,²⁰ Some authors suggest oblique coronal (parallel to the humeral shaft with the elbow slightly flexed) image planes for evaluating the collateral ligaments.¹⁹^,²¹ Reformatting thin (1 mm) GRE image blocks or three-dimensional imaging also provides the flexibility to align complex anatomic structures. Soft tissue contrast is reduced with these sequences compared to conventional or fast spin-echo (FSE) sequences.²^,³^,⁵^,²²

We begin most examinations with a coronal scout image (Table 10.1) which takes 26 seconds to perform (Fig. 10.5). Three to five 1-cm-thick images are obtained using a large FOV (32 to 40 cm).

Axial images are obtained using T1-weighted and either FSE T2-weighted or fast STIR sequences. The section thickness is typically 4 mm. Image planes are matched with the T1- and T2-weighted sequences to allow comparison of sections. Additional T2-weighted FSE images are obtained in
the coronal and sagittal planes (Table 10.1). We also obtain dual echo steady state (DESS) images in the coronal plane using 1-mm sections to better evaluate the articular cartilage and collateral ligaments. Coronal and sagittal images are oriented based upon the position of the epicondyles (Fig. 10.6).

Table 10.1 Routine Examination MRI of the Elbow and Forearm at 1.5 T

	Pulse Sequence	Slice Thickness	FOV	Matrix	Excitations (NEX)	Image Time
Scout (coronal)	15/5, FA 40	1 cm/skip 0.5 mm	32-40	256 × 128	1	26 s
Axial T1-weighted	SE 530/17	4 mm	8-12	512 × 512	1	4 min 35 s
Axial STIR Or	7,090/101, TI 160	4 mm/skip 0.04 mm	8-12	256 × 256	2	4 min 38 s
Axial T-2 weighted	4,000/102, ETL 8	4 mm/skip 0.04 mm	8-12	256 × 256	2	3 min 18 s
FSE with FS
Coronal T2-weighted	4,000/102, ETL 8	4 mm/skip 0.04 mm	8-12	256 × 256	2	3 min 18 s
FSE with FS
Coronal DESS	23.87/6.73	1 mm/22/slab	12-14	256 × 256	12	4 min 36 s
Sagittal T2-weighted	4000/102, ETL 8	4 mm/skip 0.04mm	12-14	256 × 256		3 min 18 s
FSE with FS
MR arthrography
Axial T1-weighted with FS	500/12	4 mm/skip 0.5 mm	10-14	256 × 256	1	3 min 16 s
Sagittal T1-weighted with FS	500/12	4 mm/skip 0.5 mm	10-14	256 × 256	1	3 min 16 s
Coronal T1-weighted with FS	500/12	4 mm/skip 0.5 mm	10-14	256 × 256	1	3 min 16 s
Coronal PD FSE	2,000/19	4 mm/skip 0.5 mm	10-14	256 × 256	1	3 min 30 s
Coronal T2 FSE with FS	4,140/92	4 mm/skip 0.5 mm	10-14	256 × 256	1	3 min 20 s
SE, spin echo; FA, flip angle; FSE, fast spin echo; FS, fat suppression; DESS, dual echo steady state; PD, proton density.

Figure 10.5 Coronal scout image of the elbow with axial image planes selected. The left side of the trunk is also seen due to the large (40 cm) field of view. The axis of the humerus and forearm (dark lines) must be considered to obtain true axial images. The normal carrying angle of the elbow is 3° to 29°. Therefore, axial images of the forearm need to be angled (black transverse line).

Intravenous gadolinium is commonly given to improve evaluation of synovial, osseous, and soft tissue lesions. Fat-suppressed post-contrast T1-weighted images are obtained in the two most appropriate image planes.

GRE sequences provide less soft tissue contrast, but can be useful for motion studies or reformatting to improve anatomic alignment of structures. Parameters include 400 to 450 TR, 20 TE, FA 45°, and 1-mm sections with a 256 × 256 matrix and two acquisitions.¹^,³^,⁵ Motion studies may include axial images in differing degrees of pronation and supination or sagittal images in different degrees of flexion and extension. The latter are more difficult to perform in closed high field strength magnets. Figure 10.7 demonstrates the image appearance of the pulse sequences commonly used for the elbow and forearm.

We have not performed elbow arthrography commonly in our practice. However, this technique is more optimal for loose bodies when there is no joint effusion, capsular and ligament tears, and osteochondral lesions.³^,²³^,²⁴ The elbow can be entered laterally (radio-capitellar joint) or posteriorly in the olecranon fossa. We inject 4 to 5 ccs of diluted gadolinium (1 mmol solution). Gadolinium is mixed with a solution of 50% Ropivacaine and 50% iodinated contrast. This assists with confirming needle position and confirming
that pain, if present, is intra-articular. Following injection, fat-suppressed T1-weighted images are obtained in the axial, coronal, and sagittal planes. In addition, we obtain T2-weighted fat-suppressed FSE images in the coronal plane to better evaluate the capsule and collateral ligaments.

Figure 10.6 Axial T1-weighted images with coronal (A) and sagittal (B) planes aligned with the epicondyles.

ANATOMY

Anatomy of the elbow and forearm is complex but effectively demonstrated by MRI (Figs. 10.8,10.9,10.10).²^,³^,²⁷^,²⁸^,²⁹^,³⁰

Articular Structures

The elbow articulations are formed by three osseous structures. The lower end of the humerus, consisting of the capitellum and the trochlea, articulates with the radial head and ulna, respectively (Fig. 10.9). The radial head also articulates with the adjacent radial notch of the ulna (Fig. 10.8C).²⁸^,²⁹^,³⁰ This allows the radial head to rotate, providing supination and pronation of the forearm. The trochlear notch of the olecranon surrounds almost 180° of the trochlea, making the elbow one of the most inherently stable joints in humans.³¹^,³² The distal articular surface of the humerus is tilted 30° anteriorly and there is a posterior tilt of the trochlear notch, yielding a resistance to posterior subluxation of the elbow in both flexion and extension.³² The ulnohumeral articulation is the most important stabilizer of the elbow under varus stress, providing 55% of the resistance to varus stress when the elbow is fully extended and 75% of the resistance when the elbow is flexed 90°. The remainder of the stabilization is provided by the capsuloligamentous structures.³² All articular surfaces are covered with hyaline cartilage; this cartilage is best appreciated on DESS or fat-suppressed FSE proton-density images.²^,²⁷^,³³

The articular capsule of the elbow is thin anteriorly and posteriorly. Additional support is provided anteriorly by the brachialis muscle and posteriorly by the triceps muscle (Fig. 10.11). The anterior capsule attaches to the humerus just above the radial and coronoid fossa and extends beyond the coronoid process of the ulna to the anterior portion of the annular ligament (Fig. 10.11). The posterior capsule is closely related to the triceps tendon and attaches to the humerus above the olecranon fossa, attaching inferiorly to the upper and lateral margins of the trochlear notch of the ulna, the roughened area on the lateral side of the ulna, and the annular ligament (Fig. 10.11). Medially and laterally, the capsule blends with the medial and lateral collateral ligaments (Figs. 10.11 and 10.12). The capsule is not usually clearly demonstrated on MRI unless there is an effusion or MR arthrography has been used. In this setting, it is often best appreciated on axial and sagittal images (Figs. 10.8 and 10.11). It may be difficult to separate the capsule from the brachialis muscle anteriorly and triceps tendon posteriorly.²⁷^,³⁴

Five main synovial recesses can be distinguished within the elbow joint on MRI, especially when there is a joint effusion or when MR arthrography is performed (Fig. 10.13).²⁷

The olecranon recess is the largest of the five, and is subdivided into the superior, medial, and lateral olecranon recesses. The anterior humeral recess is divided into the coronoid and radial fossae (Fig. 10.13A). The annular recess surrounds the radial neck (Fig. 10.13B). The ulnar collateral ligament (UCL) and radial collateral ligament (RCL)
recesses are deep in the respective UCL and RCL. Synovial folds of various sizes and shapes normally project into the joint space and should not be mistaken for intra-articular loose bodies.²⁷ These synovial folds usually occur at the junction of two synovial recesses or a triangular meniscuslike structure at the joint line margin.²⁷

Figure 10.7 Commonly used pulse sequences for the elbow. 3.0 T coronal T1-weighted (A) and DESS (B) sequences. The DESS sequences are particularly useful for demonstrating articular cartilage. Axial T1- (C) and fat-suppressed turbo spin-echo T2-weighted (D) images. E: Sagittal fat-suppressed turbo spin-echo T2-weighted image.

Figure 10.8 Axial proton density-weighted MR images with anatomy labeled and illustration demonstrating the level of section. A: Axial image through the supracondylar region. B: Axial image through the medial and lateral epicondyle. C: Axial image through the radial head. D: Axial image at a level just distal to the radial head. E: Axial image at the level of the radial tuberosity. F: Axial image below the tuberosity level. G: Axial image of the proximal forearm.

Figure 10.8 (continued)

Ligaments

Supplementary support for the elbow is provided medially and laterally by the radial and ulnar collateral ligament complexes (Figs. 10.12 and 10.14).²⁸^,³⁴ These ligaments can be identified on the coronal, posterior coronal oblique, and axial MR images (Fig. 10.12).²^,²⁰^,²⁷ Varus and valgus injuries to the elbow can result in disruption of either the radial or the ulnar collateral ligaments and capsule.²^,³⁴^,³⁵^,³⁶^,³⁷ Therefore, these structures need to be further defined (Fig. 10.14). Theulnar (medial) collateral ligament ismuchstronger than the radial (lateral) collateral ligament (Fig. 10.12).²³ The UCL is comprised of three bands that are in continuity with each other. The anterior band is the dominant structure and the primary constraint resisting valgus stress on the elbow.²⁸^,³⁵^,³⁸ It courses anteriorly from the anteroinferior
surface of the epicondyle to attach the medial edge of the coronoid process (Fig. 10.14A). The posterior band is smaller and has a fan-like configuration.²⁵ It extends from behind the medial epicondyle and courses slightly posteriorly to attach onto the medial aspect of the olecranon (Fig. 10.14A). The transverse band is clinically less significant, small, or sometimes absent, and is often difficult to identify on MRI.²^,³^,³⁰

Figure 10.9 Coronal image of the elbow and forearm with anatomy labeled and illustration demonstrating the section level. A: Coronal image through the posterior elbow and forearm. B: Coronal image through the mid elbow and forearm. C: Coronal image through the anterior elbow and forearm.

Figure 10.9 (continued)

The RCL complex is composed of the lateral ulnar collateral ligament, radial collateral ligament, and annular ligament (Fig. 10.14B). The lateralUCL(LUCL)originates from the lateral epicondyle, extends distally along the posterior radial head, blends with some fibers of the annular ligament, then courses obliquely and medially to attach onto the proximal supinator crest of the ulna.²⁰ The LUCL is the primary stabilizer against varus stress, and its disruption can lead to posterolateral rotatory instability of the elbow.³⁹ The radial collateral ligament arises from the anterior inferior aspect of the lateral epicondyle, deep to the common extensor tendon. It extends distally to insert onto the annular ligament and fibers of the supinator muscle (Fig. 10.14B). The annular ligament encircles the proximal radial neck and attaches anteriorly and posteriorly onto the radial notch of the ulna (Figs. 10.14B and 10.15). There is an additional ligament, the quadrate ligament, which extends between the radial neck and ulna.²⁸^,³⁸

Bursae

There are several important superficial and deep bursae about the elbow that should be emphasized because of the potential for confusion with cysts or other pathology on MRI. Superficial bursae include the olecranon, medial, and lateral epicondylar bursae. There are three potential olecranon bursae locations. The most common is the
subcutaneous olecranon bursa. There are also intratendinous and subtendinous bursae in the olecranon region (Fig. 10.16) (Table 10.2).²⁸^,³⁴ The subtendinous bursa (bicipitoradialis) is best seen on axial and sagittal MR images and should not be confused with an elbow effusion. An inflamed bursa can be differentiated from a simple effusion by the lack of fluid in the anterior compartment of the elbow. The other two superficial bursae, the medial epicondylar and lateral epicondylar, should not be confused with disruptions or tears in the medial and lateral collateral ligaments. Figure 10.17 demonstrates the location of the other superficial and deep bursa in the elbow region. The relationship of these bursae to branches of the radial and ulnar nerves (Fig. 10.17) is important.²⁷^,³⁴ These bursae are normally
not identified, but when inflamed and fluid-filled (due to trauma, infection, synovitis, or gout), they can be demonstrated on T2-weighted or GRE images.⁵ In this setting, the bursae will appear as homogeneous, high intensity structures with clearly defined margins.¹^,²

Figure 10.10 Sagittal images of the elbow and forearm with anatomy labeled and illustration demonstrating the section level. A: Sagittal image through the lateral radiocapitellar joint. B: Sagittal image through the ulnar-trochlear articulation.

Figure 10.11 MR images of the capsule of the elbow (broken lines) seen on coronal T1-weighted images anteriorly (A) and posteriorly (B) and sagittal (C) image.

Muscles of the Elbow and Forearm

The muscular anatomy of the elbow and forearm is complex (Tables 10.3 and 10.4).²⁷^,³⁴^,³⁵ Generally, there are four basic movements in the elbow and forearm. The elbow is limited to flexion and extension. Pronation and supination occurs between the radius and ulna. It should be kept in mind that in the extended position, the normal carrying angle of the elbow ranges from 3° to 29° (Fig. 10.5). When discussing the muscles of the elbow and forearm, it is simplest to discuss them based upon their function (Tables 10.3 and 10.4).²⁷^,²⁹^,³⁴

There are two major categories as described above, namely flexors and extensors, and pronators and supinators. The chief flexors of the elbow are the biceps, brachialis, and
brachioradialis (Figs. 10.8, 10.10, and 10.18) (Table 10.3). The biceps brachii crosses the elbow anteriorly to insert onto the radial tubercle and serves as a supinator and flexor (Figs. 10.3, 10.8, and 10.18).²⁷ The brachialis is a large muscle that arises from the anterior humerus and passes anterior to the elbow before inserting onto the proximal ulna near the coronoid process (Figs. 10.8, 10.9, 10.18, and 10.19). The brachioradialis arises from the radial side of the distal humerus (Fig. 10.18), crosses the lateral epicondyle, and extends distally to insert just proximal to the metaphysis of the radius (Figs. 10.8, 10.9, 10.10). In its activity as a flexor, the brachioradialis is aided by the adjacent muscles of the extensor group, especially the extensor carpi radialis longus.³^,²⁷^,³⁴ A fourth and less important flexor of the elbow is the pronator teres, which functions optimally only when the forearm is pronated. The pronator teres arises from the supracondylar
portion of the humerus, extends obliquely across the medial aspect of the elbow, and inserts onto the upper third of the radius (Figs. 10.8, 10.9, and 10.18).²⁷^,³⁴

Figure 10.12 Coronal DESS images at 3.0-T demonstrating the ulnar (arrow in A) and radial (arrow in B) collateral ligaments.

Figure 10.13 Recesses of the elbow. A: Sagittal MR arthrogram image demonstrating the olecranon (arrow) and anterior humeral (arrowhead) recesses. B: Axial MR arthrogram image demonstrating the annular recess. (Courtesy of Jeffrey J. Peterson MD, Mayo Clinic Florida.)

Figure 10.14 Lateral illustrations of the ligaments of the elbow from the medial (A) and lateral (B) sides.

Figure 10.15 Axial T1-weighted 3.0 T image demonstrating the annular ligament (arrows).

Extension of the elbow (Table 10.3) is accomplished primarily by the triceps, especially the medial head, and the anconeus (Figs. 10.8, 10.10, and 10.20). ²⁷^,²⁹ Thetriceps (Fig. 10.20) takes its origin (three heads) from the infraglenoid tubercle of the scapula, posterior humerus above the radial
groove, and the lower posterior humerus.²⁷^,³⁴ It inserts onto the olecranon. The anconeus (Figs. 10.8 and 10.20) arises from the posterior lateral epicondyle and extends distally and medially to insert onto the lateral ulna (Fig. 10.20).

Table 10.2 Elbow Bursae

Superficial

Olecranon (subcutaneous, intratendinous, subtendinous)

Medial epicondylar

Lateral epicondylar

Deep

Radiohumeral bursa

Supinator bursa

Bicipitoradial bursa

Subextensor carpi radialis brevis bursa

Ulnar nerve bursa

From Morrey BF. The Elbow and its Disorders, 4th ed. Philadelphia, PA: Elsevier/Saunders, 2009.

Figure 10.16 Illustration of the olecranon bursae. The superficial subcutaneous bursa is most commonly seen. The intratendinous and subtendinous bursae are less frequently identified.

Table 10.3 Muscles of the Elbow

Muscle	Origin	Insertion	Action	Blood Supply	Innervation
Biceps brachii	Two heads 1) Supraglenoid tubercle	1) Radial tuberosity (bursa separates tendon from tuberosity)	Elbow flexor supinator	Brachial branches	Musculocutaneous C5-C6
	2) Coracoid	2) Aponeurosis to forearm flexors
Brachialis	Low 2/3 anterior humerus	Coronoid and ulnar tuberosity	Elbow flexor	Brachial branches	Musculocutaneous C5-C6
Brachioradialis	Supracondylar ridge lateral humerus	Distal lateral radius	Elbow flexor	Radial and radial recurrent arteries	Radial C5-C6
Pronator teres	Two heads 1) Medial supracondylar ridge and interosseous membrane 2) Coronoid of ulna	Midlateral radius	Pronation accessory elbow flexor	Ulnar and recurrent ulnar arteries	Median C5-C7
Triceps brachii	Three heads 1) Infraglenoid tubercle 2) Posterior humerus above radial groove 3) Lower 2/3	Olecranon	Elbow extensor	Profunda brachii	Radial
Anconeus	Posterolateral epicondyle	Lateral olecranon and proximal ulna	Elbow extensor	Recurrent radial artery	Radial
Supinator	Lateral epicondyle, radial ligament, annular ligament, ulna	Upper lateral radius	Supination	Radial artery	Median
From Berquist TH. MRI of the Musculoskeletal System, 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2001; Rosse C, Rosse PC. Hollinshead’s textbook of anatomy. Philadelphia, PA: Lippincott-Raven, 1997; and Morrey BF. The Elbow and its Disorders, 3rd ed. Philadelphia, PA: WB Saunders, 2000.

Figure 10.17 Illustrations of the bursae of the elbow as seen (A) anteriorly and (B) posteriorly. Note the relationship of the bursae to the ulnar nerve and neural branches anteriorly. T2-weighted sagittal (C) and axial (D) images in a patient with olecranon bursitis demonstrate fluid distending the olecranon bursa (arrows).

Figure 10.17 (continued)

The main pronators of the radius and ulna are the pronator teres proximally and the pronator quadratus distally (Tables 10.3 and 10.4) (Fig. 10.21). The pronator teres (Figs. 10.8, 10.10, and 10.21) originates from the medial supracondylar ridge and coronoid of the ulna. It passes distally and laterally to insert onto the lateral aspect of the midradius.²⁷^,²⁹ The origins and insertions of the pronator quadratus are discussed in Chapter 11.

Supination is accomplished by the supinator and biceps brachii muscles, with some supination resulting from contraction of the extensor pollicis longus, abductor pollicis longus, and, to a lesser extent, the extensor carpi radialis longus and brachioradialis (Fig. 10.22).²⁷^,³⁴ The supinator (Figs. 10.10 and 10.22) originates from the lateral epicondyle, lateral collateral ligament complex, and adjacent ulna. The muscle passes distally to insert onto the upper lateral radius.²⁷^,²⁹^,³⁴ The muscles responsible for pronation are almost exclusively innervated by the median nerve, while those responsible for supination are innervated by the musculocutaneous and radial nerves (Table 10.3).²⁷

The majority of the forearm muscles arise from the humerus and cross the elbow prior to inserting distally.²⁷^,³¹^,³⁴ The flexor group arises from the medial humerus and/or ulna. This muscle group is innervated by both the median and ulnar nerves, but the median nerve is the major contributor (Table 10.4). The extensors arise from the lateral aspect of the humerus and radius and are supplied predominantly by the radial nerve (Table 10.4).²⁷

Flexors

The flexor group is divided into three layers—superficial, intermediate, and deep.²⁷ The superficial layer originates predominantly from the common flexor tendon at the medial epicondyle (Fig. 10.23). Muscles in the superficial group include the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris (Fig. 10.23) (Table 10.4). The two heads of the pronator teres originate from the common flexor tendon and the coronoid process of the elbow. The pronator teres extends under the brachialis and inserts onto the lateral aspect of the midradius. The flexor carpi radialis also originates from the common flexor tendon at the medial epicondyle and extends distally, crosses the flexor retinaculum along the groove of the trapezium, and inserts onto the second metacarpal base. Along its course, the flexor carpi radialis covers part of the flexor digitorum superficialis (Fig. 10.8). The palmaris longus arises from the common flexor tendon medially and extends for only about one-third the length of the forearm. Distally the tendinous portion crosses the wrist superficial to the flexor retinaculum (Fig. 10.23) and continues to become a part of the palmar aponeurosis in the hand. The flexor carpi ulnaris (the last of the superficial group) also has two heads, the first arising from the common flexor tendon, the second from the olecranon and posterior upper two-thirds of the ulna (Fig. 10.23). This muscle covers the ulnar nerve and vessels along much of its course in the forearm (Fig. 10.8) and crosses
the wrist through the pisohamate and pisometacarpal ligaments to insert onto the hamate hook and fifth metacarpal base.²⁷^,²⁹^,³⁰

Table 10.4 Muscles of the Forearm

Muscles	Origin	Insertion	Action	Innervation
Flexors
Superficial group
Pronator teres	Two heads 1) Medial supracondylar ridge and interosseous membrane 2) Coronoid of ulna	Midlateral radius	Pronator, elbow flexor	Median C5-C7
Flexor carpi radialis	Common flexor tendon (medial epicondyle)	Second metacarpal base	Wrist flexor	Median
Palmaris longus	Common flexor tendon (medial epicondyle)	Palmar aponeurosis	Wrist flexor	Median
Flexor carpi ulnaris	Two heads 1) Common flexor tendon 2) Upper radius and distal to tubercle	Hamate hook and 5th metacarpal base	Wrist flexor	Ulnar nerve
Intermediate group
Flexor digitorum superficialis	Two heads 1) Common flexor tendon 2) Upper radius and distal to tubercle	Base 2-5 middle phalanx	Flexion proximal interphalangeal joints	Median
Deep group
Flexor digitorum profundus	Anterior 2/3 ulna and interosseous membrane	Distal phalanges 2-5	Flexion of fingers	Median and ulnar
Flexor pollicis longus	Middle 1/3 radius and interosseous membrane	Distal phalanx thumb	Thumb flexor	Median
Pronator quadratus	Distal 1/4 anterior ulna	Distal 1/4 anterior radius	Pronation	Median
Extensors
Superficial group
Brachioradialis	Low 2/3 anterior humerus	Coronoid and ulnar tuberosity	Elbow flexor	Radial C5-C6
Extensor carpi radialis longus	Low 1/3 supracondylar ridge humerus	Radial dorsal base 2nd metacarpal	Extend wrist	Radial
Extensor carpi radialis brevis	Common extensor tendon lateral epicondyle	Base 3rd metacarpal	Extend wrist	Radial
Extensor digitorum	Common extensor tendon lateral epicondyle	Distal 2-5 phalanges	Common extensor fingers	Radial
Extensor digiti minimi	Extensor digitorum	Distal small finger	Extensor 5th finger	Radial
Extensor carpi ulnaris	Two heads 1) Common extensor tendon 2) Posterior ulnar border	Medial side base 5th metacarpal	Wrist extensor, ulnar abduction	Radial
Deep group
Abductor pollicis longus	Posterior ulna, interosseous membrane, middle posterior radius	Lateral base 1st metacarpal	Long abduction thumb	Radial
Extensor pollicis brevis	Midposterior radius	Base proximal phalanx of thumb	Extensor thumb	Radial
Extensor pollicis longus	Mid 1/3 posterior radius	Base distal phalanx of thumb	Extends phalanges of thumb	Radial
Extensor indicis	Posterior radius and interosseous membrane	Proximal phalanx index finger	Extensor index finger	Radial
From Berquist TH. MRI of the Musculoskeletal System, 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2001; Rosse C, Rosse PC. Hollinshead’s Textbook of Anatomy. Philadelphia, PA: Lippincott-Raven, 1997; and Morrey BF. The Elbow and its Disorders, 3rd ed. Philadelphia, PA: WB Saunders, 2000.

Figure 10.18 Illustration of the superficial flexor muscles of the elbow.

The flexor digitorum superficialis (sublimis) forms the intermediate layer of the flexor group (Fig. 10.24). This muscle also arises from the medial common flexor tendon; a second head originates from the upper radius, distal to the tubercle. This large, flat muscle covers the median nerve and ulnar nerve and artery as it courses distally in the forearm (Figs. 10.8 and 10.24).²⁷^,³⁰ Prior to transversing the
flexor retinaculum, the flexor digitorum superficialis gives off four tendons. After passing through the flexor retinaculum and carpal tunnel, these four tendons have common sheaths with the flexor digitorum profundus and split distally to insert onto either side of the bases of the second through fifth middle phalanges.²⁷^,²⁹^,³⁰^,³⁴

Figure 10.19 Sagittal 3.0-T fat suppressed proton density weighted image demonstrating the insertion of the brachialis muscle/tendon near the coronoid process of the ulna (arrow).

Figure 10.20 Illustration of the extensors of the elbow.

Figure 10.21 Illustration of the pronators of the forearm.

Figure 10.22 Illustration of the supinators of the forearm.

Figure 10.23 Illustration of the superficial flexor and extensor muscles of the forearm.

Figure 10.24 Illustration of the intermediate flexor compartment of the forearm.

The deep flexor group includes the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus (Fig. 10.25) (Table 10.4). The flexor digitorum profundus arises from the anterior two-thirds of the ulna in its midportion and the interosseous membrane. This muscle also divides into four tendons that join the flexor digitorum superficialis in a common tendon sheath as they pass beneath the flexor retinaculum and carpal tunnel. The tendons insert onto the bases of the distal second through fifth phalanges.²⁹^,³⁰^,³⁸ The flexor pollicis longus arises from the middle one-third of the radius and interosseous membrane and has an independent tendon sheath distally as it passes through the carpal tunnel. Thus, it is located more radially and separate from the flexor digitorum profundus and flexor digitorum superficialis tendons (Fig. 10.25). Upon leaving the carpal tunnel, the flexor pollicis longus passes through the thenar muscle region to insert onto the distal phalanx of the thumb. The third and final muscle of the deep group is the pronator quadratus, which is a flat, quadrangular muscle lying behind the flexor
digitorum longus and flexor pollicis longus. This muscle arises from the distal ulna to insert onto the distal radius in a near-transverse direction (Fig. 10.25).²⁷^,²⁸^,²⁹^,³⁴

Figure 10.25 Illustration of deep flexors of the forearm.

Extensors

The extensor muscles of the forearm are actually flexors of the elbow, as noted above. All of the extensor muscles are innervated by the radial nerve.²⁷ The extensor muscles, like the flexors, are divided into superficial and deep compartments. The superficial group includes the brachioradialis, extensor carpi radialis longus, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris (Fig. 10.26).²⁷^,²⁹^,³⁰ The brachioradialis, as described above, has a long origin above the supracondylar ridge, where it lies between the brachialis and triceps muscles. The radial nerve lies between it and the brachialis (Fig. 10.8). Superiorly, the brachioradialis partially covers the extensor carpi radialis longus as it passes distally to insert onto the lateral side of the distal radius. The extensor carpi radialis longus arises from the lower third of the anterior supracondylar ridge and is covered superiorly by the brachialis. The extensor carpi radialis longus overlaps the extensor carpi radialis brevis and gives rise to a flat tendon at the level of the mid forearm. It then accompanies its companion, the extensor carpi radialis brevis, distally. The extensor carpi radialis longus extends along the posterior radial surface deep to the abductor pollicis longus and extensor pollicis longus, passes under the extensor retinaculum (where it shares a common tendon sheath with the extensor carpi radialis brevis), and inserts onto the radial dorsal aspect of the base of the second metacarpal (Figs. 10.8, 10.9, 10.10). At this location, there may be a small bursa between the second metacarpal base and the tendon. This bursa is usually not visible on MRI unless it is inflamed and distended with fluid. The extensor carpi radialis brevis is the most lateral of the extensor muscles and arises from the common extensor tendon at the lateral epicondyle, and also has a small head that arises from the radial collateral ligament. This muscle is largely covered by the extensor carpi radialis longus in its proximal portion (Figs. 10.8 and 10.26). The extensor digitorum is located adjacent to it on the ulnar side. In the distal forearm, the muscle is separated from the extensor digitorum by the abductor pollicis longus and extensor pollicis brevis (Figs. 10.8 and 10.26). At the wrist, the tendon of the extensor carpi radialis brevis lies immediately adjacent to the ulnar side of the extensor carpi radialis longus, and both tendons share a common sheath as they pass under the extensor retinaculum. The extensor carpi radialis longus inserts onto the base of the third metacarpal. Its chief function is to extend the wrist, but it also assists in elbow flexion. The extensor digitorum (extensor digitorum communis) is the common extensor of the fingers. This muscle occupies the central
portion of the dorsal forearm. It originates from the common extensor tendon and shares an origin with the belly of the extensor digiti minimi. Distally, three to four tendons are present with a common sheath within the extensor retinaculum. The sheath is shared with the extensor digiti indicis. The tendons pass under the extensor retinaculum and receive slips from the lumbricals and interosseous muscles in the hand, thereafter dividing into central and lateral bands (see Chapter 11). The central bands insert onto the middle and lateral bands on the sides of the distal phalanges. The primary function of the extensor digitorum is to serve as an extender and abductor of the fingers. The extensor digiti minimi arises largely from a septum adjacent to the extensor digitorum and occupies a superficial position on the dorsal forearm between the extensor digitorum and extensor carpi ulnaris. The slender tendon of this muscle continues in a separate compartment under the extensor retinaculum to insert onto the dorsal aspect of the small finger in a similar fashion to the extensor digitorum. The extensor carpi ulnaris is the most medial of the superficial muscles. It has two heads, the first arising from the lateral epicondyle via the common extensor tendon, and the second from the posterior border of the ulna. The tendon of this muscle passes through a special compartment in the extensor retinaculum and also through the ulnar groove. The insertion is the medial side of the base of the fifth metacarpal. Its primary functions are wrist extension and ulnar abduction.²⁷^,²⁹^,³⁰^,³⁴

Figure 10.26 Illustration of extensor muscles of the forearm.

Deep Extensors

The deep extensors of the forearm include the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis (Fig. 10.27). The supinator is included in this group because of its position in the deep compartment (Fig. 10.8). The abductor pollicis longus is the long abductor of the thumb and arises from the posterior ulna distal to the supinator, the interosseous membrane, and the middle third of the posterior radius. This muscle passes obliquely to emerge between the extensor carpi radialis brevis and extensor digitorum with the extensor pollicis brevis medial and inferior to it (Figs. 10.8 and 10.27). The abductor pollicis longus and extensor pollicis brevis pass superficial to the radial extensor tendons and both share a common sheath at the wrist. At this level, it lies superior to the radial artery and passes to the dorsum of the hand where it inserts onto the base of the first metacarpal on its lateral side (see Chapter 11). The abductor pollicis longus serves as a radial abductor of the wrist and also a radial extender of the thumb. The extensor pollicis brevis is the short extensor of the thumb and arises from the midportion of the posterior radius distal to the abductor pollicis longus and also from the interosseous membrane. It passes between the extensor digitorum and abductor pollicis longus and crosses the wrist superficial to the radial extensors. This tendon forms the anterior boundary of the anatomic snuff box. The radial artery is deep to this tendon and the tendon of the abductor pollicis longus. The extensor pollicis brevis inserts onto the base of the proximal phalanx of the thumb, where it serves as an extensor of the thumb and radial abductor of the wrist. The extensor pollicis longus arises from the middle posterior third of the radius and interosseous membrane, is in contact with the abductor pollicis longus, and partially overlaps the extensor pollicis brevis superiorly. At the wrist, it lies on the radial side of the extensor digitorum. The tendon runs obliquely across the wrist in a separate compartment under the extensor retinaculum and in a groove just medial to the radial tubercle. It emerges to form the dorsal margin of the anatomic snuff box. Its tendon covers or is dorsal to the extensor pollicis brevis and inserts onto the base of the distal phalanx of the thumb. This muscle serves as an extensor of both phalanges of the thumb. The final muscle of the deep compartment is the extensor indicis (extensor indicis proprius), which is the extensor of the index finger. It arises distal to the extensor pollicis longus on the posterior radius and interosseous membrane, and is largely covered by the superficial muscle group along its course. The tendon passes deep to the extensor digiti minimi and deep to the extensor digitorum, with which it shares a common sheath in the dorsum of the hand. Along the dorsal aspect of the hand, the extensor indicis lies on the ulnar side of the extensor digitorum and inserts with an expansion onto the dorsal aspect of the proximal phalanx.³^,²⁷^,²⁹

Figure 10.27 Illustration of the deep extensor muscles of the forearm.

Figure 10.28 Illustrations of the neurovascular anatomy of the elbow and forearm.

Neurovascular Anatomy

Knowledge of the neurovascular anatomy and the relationship of the neurovascular structures to the various muscles and compartments of the elbow and forearm is critical for evaluating MR images (Fig. 10.28).⁴⁰ Soft tissue masses and traumatic conditions, including nerve compression syndromes involving these structures, can cause significant clinical symptoms.²^,²⁷^,³⁰^,⁴¹ Therefore, it is important that the relationship of the arteries, veins, and nerves to the various compartments and muscle groups is appreciated. Following the nerves and vessels is most easily accomplished with contiguous axial images (Fig. 10.8), especially when viewed in cine mode. Because of the variation in the course of these structures, they are rarely included in their entirety in the coronal or sagittal planes. Three-dimensional volume imaging and angiographic techniques will provide excellent visualization of the major vascular structures; however, following the course of nerves and identifying lesions in or adjacent to them will likely still be most easily accomplished on axial images.³^,³⁰^,³³

At the level of the distal humerus (Fig. 10.8A), the brachial artery is located anteromedially adjacent to its accompanying vein. The median nerve usually lies along the medial aspect at the junction of the biceps and brachialis muscles. The ulnar nerve is positioned more posteriorly along the medial aspect of the triceps (Figs. 10.8 and 10.28). At this same level, the radial nerve is most commonly seen between the brachialis muscle and brachioradialis just anterior to the lateral aspect of the supracondylar portion of the humerus. Near the elbow, the radial nerve courses anteriorly along the margin of the brachialis muscle and medial to the brachioradialis (Fig. 10.28) to a point just above the supinator, where it divides into the deep and superficial branches. Once this division has occurred, the nerve is more difficult to follow into the forearm on MR images (Fig. 10.8). However, at this point, the superficial branch of the nerve lies anterior to the extensor carpi radialis longus and the deep branch is generally seen either within or between the supinator and extensor digitorum, posterior to the radius (Figs. 10.8 and 10.28). The median nerve courses along the anterior aspect of the antecubital fossa, passes beneath the flexor digitorum superficialis, and lies between this muscle and the flexor digitorum profundus as it passes distally into the forearm (Figs. 10.24 and 10.28). The median nerve is a larger structure and usually can be easily identified on axial MR images (Fig. 10.8). The ulnar nerve passes posterior to the medial epicondyle and is clearly identified on most images at this level (Fig. 10.8). More distally, the ulnar nerve is usually located between the flexor digitorum profundus and the flexor carpi ulnaris (Figs. 10.8 and 10.28).²⁷^,³⁴

The major vessels in the elbow and forearm are more easily identified than the smaller, low signal intensity nerves. The brachial artery courses with the median nerve in the antecubital fossa prior to dividing into the radial and ulnar arteries. The radial artery lies superficial to the flexor pollicis longus as it extends into the forearm. The ulnar artery
usually accompanies the median nerve along its course superficial to the flexor digitorum profundus. Figure 10.28 demonstrates the major neurovascular anatomy of the forearm and elbow.²⁷^,⁴¹ Figure 10.29 depicts the normal MR angiogram of the elbow and proximal forearm.

Figure 10.29 Normal MR angiogram of the elbow and proximal forearm. The distal brachial artery (large arrow), proximal radial (large double arrows), and ulnar (open arrow) arteries are illustrated. The proximal portions of the anterior and posterior ulnar recurrent arteries (curved arrow), anterior and posterior interosseous arteries (small arrowheads), and posterior interosseous recurrent artery (large arrowhead) are well visualized.

PITFALLS

Pitfalls when interpreting MRIs of the elbow and forearm are usually related to normal anatomic variants, technical errors, improper coil selection, patient motion or flow, and other imaging artifacts.¹^,²^,⁴²^,⁴³^,⁴⁴^,⁴⁵

The list of normal anatomic variants involving the elbow and forearm is potentially long. A frequent osseous variant is the supracondylar process. This hook-like, bony projection is a vestigial remnant that is also seen in birds, and is usually noted 1 to 2 inches above the medial epicondyle in humans. This structure is almost always asymptomatic. However, a ligamentous structure (ligament of Struthers) can extend from the supracondylar process to the medial epicondyle and compress the median nerve or brachial artery.²⁷^,⁴⁶^,⁴⁷ Identification of the supracondylar process is easily accomplished with routine radiography. However, the relationship of the ligament of Struthers to the neurovascular structures may be most easily viewed with coronal and axial MRI.²

Rosenberg et al.⁴²^,⁴⁵ described a pseudodefect at the junction of the capitellum and lateral epicondyle (Fig. 10.30) that should not be confused with osteochondritis dissecans or an osteochondral impaction fracture. This pseudodefect is due to a normal osseous groove in this region that can give the appearance of an osteochondral abnormality on axial, sagittal, and coronal MR images. The pseudodefect deepens as the images proceed more laterally. Occasionally, one or more fine, low signal lines extend from the pseudodefect into the marrow; these should not be mistaken for fractures.⁴²^,⁴⁵^,⁴⁸ Similarly, there is normally a transverse
ridge in the trochlear notch that is not covered with hyaline cartilage. This finding is most easily appreciated on sagittal images and should not be mistaken for a cartilage lesion (Fig. 10.31).⁴⁴

Figure 10.30 Capitellar pseudodefect. Coronal T1-weighted (A) and fat suppressed proton density turbo spin-echo T-2 weighted (B) images demonstrating the normal variant. There is no marrow edema to suggest active impaction.

Figure 10.31 Trochlear notch. Sagittal turbo spin-echo fat-suppressed proton density image demonstrating the normal trochlear notch (arrow).

Soft tissue anomalies, including combination of muscle bellies, accessory origins or absence of one of the heads when multiple origins are present, and total absence (palmaris longus 12.9%) are not unusual. These changes are not usually clinically significant.²³ Certain anomalous muscles can be significant. The anconeus epitrochlearis is present in place of the cubital tunnel retinaculum in up to 11% of patients. This can result in ulnar nerve compression (Fig. 10.32).³⁴^,⁴⁴ Readers are referred to anatomic references for a more complete discussion of normal anatomic variants.²⁷^,⁴⁴^,⁴⁵^,⁴⁶^,⁴⁷^,⁴⁸

Figure 10.32 Axial T1-weighted image of the elbow demonstrates an anconeus epitrochlearis (arrow) compressing the ulnar nerve (arrowhead).

Other errors in interpretation of MR images are due to improper choice of pulse sequences, image planes, coils, and patient position (see Chapter 3). Many mistakes can be avoided by careful review of clinical history and physical findings.

Image artifacts have been more fully discussed in Chapters 1 and 3. Most artifacts in the upper extremity are due to motion and/or flow artifacts.¹^,⁴⁹^,⁵⁰^,⁵¹^,⁵²^,⁵³ Flow artifacts may also create problems in image interpretation. Flow artifact suppression techniques (see Chapter 3) can reduce artifacts;
however, it is still useful to change the phase encoding direction to prevent artifacts from degrading important areas on the image (Fig. 10.33).¹^,²^,⁵³

Figure 10.33 Flow artifact. Axial images of the elbow showing flow artifact in the (A) vertical y-axis and (B) transverse or x-axis. The ulnar nerve region (small arrowhead) is distorted by flow artifact (large arrowheads) in A, which could interfere with diagnosis of pathology in this region.

Pitfalls may also be avoided by comparing radiographs and other imaging modalities with MRI. Metal artifact can cause significant signal intensity distortion. Knowledge of the type of implant is useful to select the proper pulse sequence parameters to reduce the artifact or confirm that MRI would not be useful.²^,³ Titanium implants cause less artifact due to reduced ferromagnetic content.

Heterotopic calcification or ossification is common about the elbow, especially at the flexor and extensor tendon attachments. Signal intensity may vary depending upon the presence of marrow in ossifications. Calcifications are low signal intensity on all pulse sequences.⁵⁴

The presence of joint effusion on radiographs after trauma has been considered synonymous with occult fracture. However, in children this may not be the case.⁵⁵^,⁵⁶^,⁵⁷ Donnelly et al.⁵⁵

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