Anatomy of the elbow joint

Osseous structures of the elbow

The elbow joint is one of the most congruent and constrained joints in the body. The elbow joint consists of the ulnohumeral joint, the radiocapitellar joint, and the proximal radioulnar joint which are all located within a single synovium-lined joint capsule (Fig. 1). The elbow joint is best classified as a trochoginglymoid joint which allows for two types of motion: flexion-extension and axial rotation. The ulnohumeral joint is a hinge or ginglymoid joint which allows for approximately 150° of elbow flexion. The radiocapitellar and proximal radioulnar joints are trochoid joints which allow for approximately 75° of forearm pronation and 85° of forearm supination [1].

Fig. 1
figure 1

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the elbow in a cadaveric specimen. The elbow joint consists of the ulnohumeral joint (short black arrow), the radiocapitellar joint (long black arrow), and the proximal radioulnar joint (arrowhead) which are all located within a single synovium-lined joint capsule.

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The ulnohumeral joint consists of the articulation of the trochlea of the humerus with the sigmoid notch of the ulna. The trochlea is the hyperboloid-shaped distal articular surface of the humerus which is covered by hyaline cartilage over an arc of approximately 330°. The trochlea consists of a lateral surface and a larger and more distally projecting medial surface which are separated by the trochlear groove (Fig. 2). The sigmoid notch is an ellipsoid shaped depression in the proximal ulna between the coronoid process and the tip of the olecranon process which forms an arc of approximately 190° in the lateral plane (Fig. 3). The sigmoid notch is not completely covered by hyaline cartilage. In most individuals, a transverse trochlear ridge is present at the junction of the coronoid process and olecranon process which divides the sigmoid notch into fairly equal anterior and posterior halves. During extension of the elbow, the tip of the olecranon process of the proximal ulna inserts into the olecranon fossa of the distal humerus (Fig. 4). During flexion of the elbow, the coronoid process of the proximal ulna inserts into the large coronoid fossa of the distal humerus which is located immediately superior to the trochlea (Fig. 5) [1]. The congruent articulation between the trochlea of the humerus and the sigmoid notch of the ulna accounts for a significant proportion of the stability of the elbow joint but only at the extremes of elbow flexion and extension [2, 3].

Fig. 2
figure 2

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the distal humerus in a cadaveric specimen. The trochlea consists of a lateral surface (short white arrow) and a larger and more distally projecting medial surface (long white arrow) which are separated by the trochlear groove (short black arrow). Also note the capitellum (long open arrow) and the medial epicondyle (short open arrow).

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Fig. 3
figure 3

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the proximal ulna in a cadaveric specimen. The sigmoid notch (long arrow) is an ellipsoid-shaped depression in the proximal ulna between the coronoid process (short arrow) and the tip of the olecranon process (arrowhead).

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Fig. 4
figure 4

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the elbow in a cadaveric specimen. During extension of the elbow, the tip of the olecranon process of the proximal ulna (arrow) inserts into the olecranon fossa of the distal humerus (arrowheads).

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Fig. 5
figure 5

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the distal humerus in a cadaveric specimen. Note the coronoid fossa (arrow) and radial fossa (arrowhead) on the anterior surface of the distal humerus. During flexion of the elbow, the coronoid process of the proximal ulna inserts into the coronoid fossa and the radial head inserts into the radial fossa.

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The radiocapitellar joint consists of the articulation of the capitellum of the humerus with the radial head. The capitellum is the spheroidal-shaped distal articular surface of the humerus which is almost completely covered with hyaline cartilage. The capitellum is separated from the trochlea by a groove which articulates with the rim of the radial head throughout the range of motion of the elbow joint (Fig. 2). The concave proximal surface of the radial head articulates with the capitellum and is completely covered with articular cartilage (Fig. 6). During flexion of the elbow, the radial head inserts into the radial fossa of the distal humerus which is located superior to the articular surface of the capitellum (Fig. 5) [1].

Fig. 6
figure 6

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the elbow in a cadaveric specimen. The concave proximal surface of the radial head (arrow) articulates with the capitellum (arrowhead).

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The proximal radioulnar joint consists of the articulation of the radial head with the semilunar notch of the proximal ulna. The semilunar or lesser sigmoid notch is a depression within the proximal ulna located just distal to the lateral aspect of the coronoid process (Fig. 7). The lesser sigmoid notch forms an arc of approximately 70° and is divided into medial and lateral portions by a small groove. Hyaline cartilage completely covers the semilunar notch. Hyaline cartilage also covers approximately 240° of the outside circumference of the radial head. It is this portion of the radial head which articulates with the semilunar notch of the proximal ulna throughout the range of pronation and supination of the elbow (Fig. 8). The anterolateral third of the circumference of the radial head is not covered by articular cartilage [1].

Fig. 7
figure 7

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the distal humerus and proximal ulna in a cadaveric specimen. The semilunar or lesser sigmoid notch is a depression within the proximal ulna (arrowhead) located just distal to the lateral aspect of the coronoid process (arrow).

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Ligamentous structures of the elbow

The medial collateral ligament, or ulnar collateral ligament, consists of three distinct components: the anterior or oblique bundle; the posterior bundle; and the transverse bundle (Fig. 9). The anterior bundle of the medial collateral ligament originates from the central portion of the anterior inferior surface of the medial epicondyle just posterior to the axis of rotation of the elbow joint. The anterior bundle consists of an anterior band and a posterior band which both insert on the sublime tubercle on the medial aspect of the base of the coronoid process of the ulna. The anterior band is taut between 0 and 60° of flexion, while the posterior band is taut between 60 and 120° of flexion. The posterior bundle of the medial collateral originates from the posterior surface of the medial epicondyle and inserts on the medial aspect of the olecranon process of the ulna. The posterior bundle is more of a fan-shaped thickening of the posterior capsule of the elbow joint than a distinct well-defined ligamentous structure. The transverse bundle of the medial collateral ligament consist of horizontal fibers running along the medial joint capsule from the coronoid process to the tip of the olecranon process of the ulna. The transverse bundle is variable in size and is often difficult to distinguish from the adjacent elbow joint capsule. The anterior band and to a lesser extent the posterior band of the anterior bundle of the medial collateral ligament accounts for the vast majority of the stability of the elbow joint against valgus and internal rotatory stress. The posterior bundle of the medial collateral ligament is a secondary stabilizer of the elbow joint against valgus and internal rotatory stress but only at 120° of elbow flexion. The transverse bundle does not provide any stability to the elbow joint since the ligament both originates and inserts on the proximal ulna [4, 5, 6, 7, 8, 9, 10, 11].

Fig. 8
figure 8

Normal anatomy of the elbow. Three-dimensional surface-shaded display CT reformat image of the elbow in a cadaveric specimen. The radial head (arrowhead) articulates with the semilunar notch of the proximal ulna (arrow).

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The lateral collateral ligament consists of three distinct components: the radial collateral ligament; the annular ligament; and the ulnar band of the lateral collateral ligament (Fig. 10). The radial collateral ligament originates from the lateral epicondyle of the humerus and extends distally to blend into the fibers of the annular ligament. The annular ligament is a thick band which completely encircles the radial head. The anterior portion of the annular ligament attaches to the anterior aspect of the sigmoid notch, while the posterior portion of the ligament expands and divides into several bands which attach to the posterior edge of the sigmoid notch. The ulnar band of the lateral collateral ligament arises from the lateral epicondyle of the humerus and extends distally to insert on the tubercle of the supinator crest of the proximal ulna immediately distal to the insertion of the annular ligament. The proximal fibers of the ulnar band of the lateral collateral ligament cannot be distinguished from the proximal fibers of the radial collateral ligament. The distal fibers of the ulnar band of the lateral collateral ligament adhere closely to the intermuscular fascia of the extensor carpi ulnaris muscle and supinator muscle. The ulnar band of the lateral collateral ligament and the annular ligament, which coalesce to insert broadly on the proximal aspect of the ulna, together account for the vast majority of the stability of the elbow joint against varus and external rotatory stress. The annular ligament also functions to stabilize the proximal radioulnar joint [12, 13, 14].

Fig. 9
figure 9

Normal anatomy of the medial collateral ligament of the elbow. The medial collateral ligament consists of three distinct components: the anterior or oblique bundle (black arrow); the posterior bundle (white arrow); and the transverse bundle (arrowhead). (Adapted from [8])

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Fig. 10
figure 10

Normal anatomy of the lateral collateral ligament. The lateral collateral ligament consists of three distinct components: the radial collateral ligament (black arrow); the annular ligament (arrowhead), and the ulnar band of the lateral collateral ligament (white arrow). (Adapted from [14])

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Muscular and tendonous structures of the elbow

Many muscles surround the elbow joint. The musculature of the elbow is divided into anterior, posterior, medial, and lateral muscle compartments.

The anterior muscle compartment is comprised of the brachialis muscle and biceps muscle which both function to flex the elbow. The brachialis muscle arises from the anterior surface of the distal humerus and inserts along the base of the coronoid process and into the tuberosity of the ulna. The biceps muscle is superficial to the brachialis muscle in the distal arm, and its tendon passes through the cubital fossa to insert on the posterior aspect of the radial tuberosity. The bicipitoradial bursa separates the distal biceps tendon from the anterior aspect of the radial tuberosity. The bicipital aponeurosis or lacertus fibrosis is the continuation of the anterior medial fascia surrounding the distal biceps muscle which courses over the median nerve and brachial artery to insert into the deep fascia of the forearm (Figs. 11, 12) [1].

Fig. 11
figure 11

Normal anatomy of the elbow. A Axial T1-weighted spin-echo image of the elbow at the level of the distal humerus. Note the pronator teres muscle (1), biceps muscle (2), brachialis muscle (3), brachioradialis muscle (4), extensor carpi radialis longus muscle (5), triceps muscle (6), and ulnar nerve (arrow). B Axial T1-weighted spin-echo image of the elbow slightly distal to the previous image. Note the pronator teres muscle (1), brachialis muscle (2), brachioradialis muscle (3), extensor carpi radialis longus muscle (4), ulnar nerve (arrow 1), cubital tunnel retinaculum (arrow 2), common flexor tendon (arrow 3), median nerve (arrow 4), brachial artery (arrow 5), biceps tendon (arrow 6), and common extensor tendon (arrow 7). C Axial T1-weighted spin-echo image of the elbow slightly distal to the previous image. Note the flexor carpi ulnaris muscle (1), flexor digitorum superficialis muscle (2), flexor carpi radialis muscle (3), pronator tere muscle (4), brachialis muscle (5), brachioradialis muscle (6), extensor carpi radialis longus and breves muscles (7), extensor digitorum muscle (8), anconeus muscle (9), ulnar nerve (arrow 1), median nerve (arrow 2), bicipital aponeurosis (arrow 3), biceps tendon (arrow 4), and branches of radial nerve with adjacent branches of radial artery (arrow 5). D Axial T1-weighted spin-echo image of the elbow slightly distal to the previous image. Note the flexor digitorum profundus muscle (1), flexor carpi ulnaris muscle (2), flexor digitorum superficialis muscle (3), flexor carpi radialis muscle (4), pronator teres muscle (5), brachioradialis muscle (6), extensor carpi radialis longus and brevis muscles (7), extensor digitorum muscle (8) extensor carpi ulnaris muscle (9), anconeus muscle (10), deep head of the supinator muscle (11), superficial head of the supinator muscle (12), ulnar nerve (arrow 1), brachialis tendon (arrow 2), biceps tendon (arrow 3), and posterior interosseous nerve with adjacent posterior interosseous artery (arrow 4)

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Fig. 12
figure 12

Normal anatomy of the elbow. Sagittal T1-weighted spin-echo image of the elbow. Note the biceps tendon (open arrow), brachialis muscle (white arrow), and triceps tendon (black arrow)

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The posterior muscle compartment is comprised of the triceps muscle, anconeous muscle, and anconeus epitrochlearis muscle. The triceps muscle consist of medial, lateral, and long heads which blend together to form a single musculotendonous unit which inserts into the tip of the olecranon process of the proximal ulna. The olecranon bursa separates the triceps tendon from the olecranon process. The triceps muscle functions to extend the elbow. The anconeous muscle arises from the posterior portion of the lateral epicondyle and inserts into the posterior lateral surface of the proximal ulna [1]. The anconeous muscle covers the lateral aspect of the radial head and annular ligament and may play a minor role in stabilizing the elbow joint [15]. The anconeus epitrochlearis muscle is an accessory muscle which is present in 3–28% of elbows. When present, the anconeus epitrochlearis replaces the cubital tunnel retinaculum and extends from the medial humeral epicondyle to the tip of the olecranon process of the proximal ulna (Figs. 11, 12) [16].

The medial compartment is comprised of the pronator teres muscle, flexor carpi radialis muscle, palmaris longus muscle, flexor carpi ulnaris muscle, and flexor digitorum superficialis muscle which function to flex the wrist and pronate the forearm. These muscles all originate from the medial epicondyle by way of the common flexor tendon. The pronator teres muscle and flexor carpi ulnaris muscle also arise from the coronoid process and proximal medial aspect of the ulna, while the flexor digitorum superficialis muscle also arises from the proximal portion of the radius (Fig. 11) [1]. The flexor carpi ulnaris and to a lesser extent the flexor digitorum superficialis muscle overlie the anterior band of the medial collateral ligament and play a secondary role in dynamically stabilizing the elbow joint against valgus stress [17].

The lateral muscle compartment consists of the brachioradialis muscle, extensor carpi radialis longus and brevis muscles, extensor digitorum muscle, extensor carpi ulnaris muscle, and supinator muscle which all function to extend the wrist and supinator the forearm. The brachioradialis and extensor carpi radialis longus muscles originate from the anterior lateral surface of the distal humerus. The extensor carpi radialis muscle, extensor digitorum muscle, and extensor carpi ulnaris muscle all arise from the lateral epicondyle by way of the common extensor tendon. The extensor carpi ulnaris also arises from the superior aspect of the aponeurosis of the anconeous muscle. The supinator muscle originates from the anterior aspect of the lateral epicondyle and from the lateral proximal crest of the ulna. The muscle extends distally and radially to wrap around and diffusely insert onto the proximal ulna (Fig. 11) [1]. The proximal fascial bands and intermuscular septa of the muscles of the lateral compartment, especially the extensor carpi ulnaris muscle and supinator muscle, play a secondary role in dynamically stabilizing the elbow joint against varus stress [11].

Nerves of the elbow

The major nerves which traverse the elbow joint include the radial nerve, the median nerve, and the ulnar nerve. These nerves all arise from the brachial plexus and provide sensory and motor innervation to the soft tissue structures of the upper extremity [1].

The radial nerve is a continuation of the posterior cord of the brachial plexus. Within the upper arm, the nerve courses distally and laterally within the spiral groove of the humerus. The nerve then penetrates the lateral intermuscular septum and enters into the anterior compartment of the arm accompanied by the deep branch of the radial artery. The radial nerve gives rise to motor branches which innervates the medial and lateral heads of the triceps muscle and the brachioradialis muscle. The radial nerve then courses distally deep to the fascia of the brachioradialis muscle before dividing into its two major branches, the posterior interosseous nerve and the superficial radial nerve, at the level of the radiocapitellar joint. The posterior interosseous nerve passes between the superficial and deep heads of the supinator muscle and courses distally through the posterior compartment of the forearm accompanied by the posterior interosseous artery [1]. The proximal edge of the superficial head of the supinator muscle may form a fibrous arch, referred to as the arcade of Frohse, through which the posterior interosseous nerve passes [18]. The posterior interosseous nerve innervates the extensor carpi radialis longus and brevis muscles, the extensor digitorum muscle, the extensor carpi ulnaris muscle, the anconeus muscle, the extensor pollicis longus and brevis muscles, the extensor indicis muscle, and the abductor pollicis longus muscle. The superficial radial nerve courses distally into the forearm between the supinator muscle and the brachioradialis muscle. The superficial radial nerve gives rise to sensory branches which innervate the dorsal soft tissue of the forearm (Fig. 11) [1].

The median nerve is formed from branches of the medial and lateral cords of the brachial plexus. The nerve courses distally within the anterior compartment of the upper arm superficial to the brachialis muscle. The median nerve passes beneath the bicipital aponeurosis into the antecubital fossa where it lies medial to the biceps tendon and brachial artery. The nerve then passes between the humeral head and the ulnar head of the pronator teres muscle. The median nerve gives rise to motor branches which innervate the pronator teres muscle, the flexor carpi radialis muscle, the palmaris longus muscle, and the flexor digitorum superficialis muscle. The median nerve then gives rise to its main branch, the anterior interosseous nerve, near the inferior border of the pronator teres muscle. The anterior interosseous nerve courses distally through the anterior compartment of the forearm between the flexor digitorum superficialis muscle and the flexor digitorum profundus muscle. The anterior interosseous nerve innervates the flexor pollicis longus muscle and the lateral portion of the flexor digitorum profundus muscle (Fig. 11) [1].

The ulnar nerve arises from the medial cord of the brachial plexus. Within the upper arm, the nerve courses distally along the medial margin of the triceps muscle accompanied by the superior ulnar collateral branch of the brachial artery and the ulnar collateral branch of the radial artery. The nerve then passes from the anterior compartment to the posterior compartment of the upper arm through the arcade of Struthers approximately 8 cm proximal to the medial epicondyle. The arcade of Struthers is a thick fascial band running from the medial head of the triceps muscle to the medial intermuscular septum. The ulnar nerve then passes through the cubital tunnel where it lies within a groove in the posterior aspect of the medial epicondyle of the distal humerus [1]. The floor of the cubital tunnel is formed by the posterior bundle of the ulnar collateral ligament. The roof of the cubital tunnel is formed by the cubital tunnel retinaculum and the deep layer of the aponeurosis of the of the flexor carpi ulnaris muscle. The cubital tunnel retinicalum is an aponeurotic-like band which originates from the tip of the medial epicondyle and inserts onto the olecranon process and into the margin of the triceps fascia. The cubital tunnel retinaculum may be completely absent or may be replaced by the anconeus epitrochlearis muscle [19]. After coursing through the cubital tunnel, the ulnar nerve passes between the humeral and ulnar heads of the flexor carpi ulnaris muscles. The nerve then courses distally through the anterior compartment of the forearm between the flexor carpi ulnaris muscle and the flexor digitorum profundus muscle. The ulnar nerve gives rise to motor branches which innervate the flexor carpi ulnaris muscle and the medial portion of the flexor digitorum profundus muscle (Fig. 11) [1].

Imaging technique

Magnetic resonance imaging of the elbow is best performed on a high field strength magnet. A surface coil is essential for obtaining high-quality images. A variety of coils may be used for imaging the elbow. A wrist coil can be used in small adults and children when a large field of view is not needed. Larger patients can be imaged with a flexible coil, anterior neck coil, shoulder coil, or knee coil. A larger coil, such as the shoulder or knee coil, is especially useful when the patient cannot fully extend the elbow or when the patient needs to be imaged in the prone position with the arm overhead.

The elbow is best imaged with the patient supine and with the arm in the anatomic position at the patient’s side. This is the most comfortable position for the patient which decreases the likelihood of patient motion during the examination. This position also minimizes the rotation of the forearm and the proximal radioulnar joint with respect to the distal humerus which optimizes visualization of the collateral ligaments and common flexor and extensor tendons in the coronal plane. For large patients and for scanners which do not allow off-center imaging, the patient can be positioned in the prone position with the arm overhead. This position places the elbow joint close to the isocenter of the scanner and thereby improves image quality; however, the prone position is relatively uncomfortable for the patient which increases the likelihood of patient motion during the examination. This position also results in significant forearm pronation and radioulnar joint rotation which makes it more difficult to evaluate the collateral ligaments and common flexor and extensor tendons in the coronal plane.

A routine imaging protocol of the elbow should include sequences in the axial, coronal, and sagittal planes. Axial images should ideally be performed in a plane perpendicular to the long axis of the humerus, radius, and ulna with the elbow in a fully extended position. Axial images should extend from the level of the distal humeral metaphysis superiorly to the level of the radial tuberosity inferiorly. Coronal images are usually obtained parallel to a line bisecting both humeral epicondyles on an axial source image; however, a cadaver study has shown that the collateral ligaments of the elbow are optimally visualized in a 20° posterior oblique coronal plane in relation to the humeral diaphysis with the elbow extended and a coronal plane aligned with the humeral diaphysis with the elbow flexed 20–30°. These modified coronal planes are obtained using a sagittal scout image (Fig. 13) [20]. Sagittal images should be obtained in a plane orthoganol to the coronal images.

Fig. 13
figure 13

Modified oblique coronal plane of the elbow used to optimally image the collateral ligaments. Sagittal T1-weighted spin-echo scout image of the elbow shows the modified oblique coronal plane (multiple lines) oriented 20° posterior to the long axis of the humeral diaphysis (bold line).

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The exact sequences which used during routine imaging of the elbow vary considerably from institution to institution. At our institution, the routine elbow protocol consists of T1-weighted fast spin-echo sequences and fat-suppressed T2-weighted fast spin-echo sequences in the axial, coronal, and sagittal planes. All sequences are performed with a field of view between 12 and 14 cm and a matrix of 256×192 pixels or 256×256 pixels. Axial images of the elbow are acquired with a slice thickness of 4 mm and an interslice gap of 1 mm, while coronal and sagittal images are acquired with a slice thickness of 3 mm and an interslice gap of 0.2 mm. A T2-weighted fast spin-echo sequence with chemical fat suppression is especially useful for identifying subtle edema within the osseous and soft tissue structures of the elbow and should be obtained in at least one imaging plane. A short-tau inversion recovery (STIR) sequence can be used instead of a fat-suppressed T2-weighted fast spin-echo sequence especially when using imaging systems with poor chemical fat suppression. The routine use of gradient-echo sequences when imaging the elbow is controversial. Some musculoskeletal radiologists believe that T2*-weighted gradient-echo sequences produce images with excellent spatial resolution which are especially helpful in evaluating the collateral ligaments of the elbow [21, 22, 23, 24]. Other musculoskeletal radiologists do not find gradient-echo sequences particularly helpful in evaluating the elbow and do not include these sequences in their routine imaging protocol [25, 26, 27]. Gradient-echo sequences are very sensitive to magnetic susceptibility changes and should not be routinely used in patients with a history of prior elbow surgery.

Magnetic resonance arthrography of the elbow is very helpful in evaluating for intra-articular loose bodies, unstable osteochondral defects, and tears of the collateral ligaments. Both normal saline or a dilute gadolinium solution containing a mixture of 1 part gadolinium and 250 parts normal saline can be used as intra-articular contrast. When performing magnetic resonance arthrography, a 22-guage needle is first inserted into the radiocapitellar joint under fluoroscopic guidance. The needle is usually inserted into the radiocapitellar joint using a lateral approach. Alternatively, the needle can be inserted using a posterior approach just proximal to the olecranon between the bony prominences of the medial and lateral epicondyles. After confirming proper positioning of the needle with a small amount of iodinated contrast material, approximately 5–10 cc of normal saline or a dilute gadolinium solution is injected into the elbow joint. When performing magnetic resonance arthrography with gadolinium contrast, fat-suppressed T1-weighted spin-echo images of the elbow should be performed in multiple planes to take advantage of the short T1 relaxation time of gadolinium. The imaging protocol should also include fat-suppressed T2-weighted fast spin-echo images or STIR images in at least one plane in order to detect osseous contusions, tendon injuries, partial thickness superficial collateral ligament tears, and other extra-articular abnormalities of the elbow [28].

Osseous abnormalities

Panner’s disease and osteochondritis dissecans of the elbow

Panner’s disease and osteochondritis dissecans are commonly used synonymously to describe osteochondral lesions of the humeral capitellum in young individuals. It is possible that these two conditions represent different stages of the same patholothic process affecting the developing capitellar epiphysis; however, Panner’s disease and osteochondritis dissecans of the capitellum should be consider two distinct conditions as they affect different patient populations and have different clinical outcomes.

Panner’s disease is an osteochondrosis of the humeral capitellum. The condition usually affects males between the ages of 7 and 12 years and occurs during the period of active ossification of the capitellar epiphysis. Patients usually present with pain, swelling, and tenderness over the lateral aspect of the elbow. Radiographs show fragmentation of the capitellar ossification center with irregular areas of relative sclerosis intermixed with areas of rarefaction. The entire capitellar epiphysis may be involved. Panner’s disease is always a benign, self-limiting condition. Osteochondral loose bodies never form, and the capitellar epiphysis eventual assumes a normal appearance as growth progresses. Due to its benign clinical course, magnetic resonance imaging is rarely used to evaluate patients with Panner’s disease [29].

Osteochondritis dissecans of the humeral capitellum, on the other hand, usually affects males between the ages of 12 and 15 years and occurs at a time when the capitellar epiphysis is almost completely ossified. The exact etiology of osteochondritis dissecans of the capitellum is presently unknown. Most authors believe that repetitive trauma to the poorly vascularized capitellum is the primary cause of osteochondritis dissecans. Most individuals with osteochondritis dissecans of the capitellum have a history of frequent repetitive overuse of the elbow. The condition primarily occurs in the dominant elbow of young male baseball pitchers or less commonly in the elbow of young female gymnasts [30, 31, 33, 33, 34, 35]. Osteochondritis dissecans usually occurs in the anterolateral aspect of the capitellar epiphysis. The blood supply to this region of the distal humeral epiphysis is tenuous and consists of end arterioles with no connection to adjacent metaphyseal vessels [36]. Genetic factors may also play a role in the pathogenesis of osteochondritis dissecans. There are various reports of osteochondritis dissecans of the capitellum occurring in multiple members of the same family [37, 38]. In addition, osteochondritis dissecans of the capitellum may occur in both elbows of the same individual [39, 40]. Biomechanical differences in the articular cartilage of the radial head and capitellum may also play a role in the development of osteochondritis dissecans. The central portion of the radial head is significantly stiffer than the adjacent capitellum. The disparity in the mechanical properties of the central radial head and lateral capitellum results in increased strain in the lateral capitellum during high valgus stress activities [41]. While osteochondritis dissecans of the elbow almost always involves the capitellum, there are rare reports of osteochondritis dissecans involving the trochlea, radial head, and olecranon [39, 40, 42].

Most individuals with osteochondritis dissecans of the capitellum present during the adolescent period with pain, tenderness, and swelling over the lateral aspect of the elbow [30, 31, 32, 33, 34, 35]. Radiographs are the initial study of choice for the diagnosis of osteochondritis dissecans of the capitellum. Radiographs performed in the early stages of the osteochondritis dissecans may be normal or show only subtle changes within the capitellum. As the disease progresses, flattening of the contour, focal rarefaction, and nondisplaced fragmentation of the subchondral bone of the capitellum becomes evident. In the late stages of the disease, a focal defect of the articular surface of the capitellum with an associated loose body can often be seen [43].

Magnetic resonance imaging can also be used to evaluate patients with osteochondritis dissecans of the capitellum (Fig. 14). Cases of early osteochondritis dissecans of the capitellum have been described on magnetic resonance imaging as focal areas of low signal intensity on T1-weighted images which appear normal on T2*-weighted gradient-echo images [44]. Two distinct signal intensity patterns of osteochondritis dissecans of the capitellum on magnetic resonance imaging have been recently described. The type-I pattern consists of a focal area of intermediate intensity signal surrounded by a low signal intensity ring on T1-weighted images. The inner most portion of the low signal intensity ring becomes high signal intensity on T2-weighted images. The type-II pattern consists of a focal area of homogenous low signal intensity on T1-weighted images and homogeneously high signal intensity on T2-weighted images. The exact clinical significance of these two patterns of osteochondritis dissecans of the elbow is presently unknown [45].

Fig. 14
figure 14

Osteochondritis dissecans of the capitellum in a 15-year-old male baseball pitcher with lateral elbow pain. A Coronal T1-weighted spin-echo image of the elbow shows a focal area of intermediate signal intensity within the anterior capitellum (arrow). B Coronal fat-suppressed T2-weighted fast spin-echo image of the elbow at the same location shows high signal intensity edema (arrow) surrounding the osteochondritis dissecans fragment (arrowhead).

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When evaluating the elbow on magnetic resonance imaging, it is important not to mistake the normal pseudodefect of the capitellum for an area of osteochondritis dissecans. The pseudodefect of the capitellum is caused by the abrupt transition between the smooth articular surface of the posterior inferior aspect of the capitellum and the rough nonarticular surface of the adjacent lateral epicondyle. This pseudodefect should be recognized as a normal anatomic variant and should not be confused with osteochondritis dissecans which is located more anteriorly within the capitellum (Fig. 15) [46].

Fig. 15
figure 15

Pseudodefect of the capitellum. A Coronal T1-weighted spin-echo image of the elbow shows the smooth articular surface of the posterior capitellum (arrow). B Coronal T1-weighted spin-echo image of the elbow immediately posterior to the previous image shows the irregular surface of the central aspect of the lateral humeral epicondyle (arrow). This should not be mistaken for an articular surface defect of the posterior capitellum.

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The key to sussessful treatment of osteochondritis dissecans of the capitellum is early detection of the disorder. Once radiographic changes are noted, more than half of patients with osteochondritis dissecans who are treated both conservatively and with surgical intervention remain symptomatic at long-term follow-up [32, 47]. Magnetic resonance imaging is superior to plain-film radiographs in the early detection of osteochondritis dissecans of the capitellum [44]. Magnetic resonance imaging is also superior to plain-film radiographs in evaluating the size, location, stability, and viability of the osteochondritis dissecans fragment. These factors are all important when determining the best treatment option in patients with osteochondritis dissecans of the capitellum [48].

An osteochondritis dissecans fragment is thought to be unstable on magnetic resonance imaging if it is surrounded by fluid signal intensity cysts or by a complete high signal intensity ring on T2-weighted images [49, 50]. Intravenous gadolinium contrast can be used during magnetic resonance imaging to evaluate the viability and stability of an osteochondritis dissecans fragment. Enhancement of the osteochondritis dissecans fragment on post-contrast images suggests that the fragment is viable and has a good blood supply. In addition, the presence of a ring of diffuse enhancement between an osteochondritis dissecans fragment and the adjacent subchondral bone of the capitellum is thought to represent granulation tissue and suggests that the fragment is unstable [51].

Magnetic resonance arthrography can also be used to determine the stability of an osteochondritis dissecans fragment. The presence of intraarticular contrast material around an ostechondritis dissecans fragment indicates disruption of the articular surface and suggests that the fragment is unstable [52].

The treatment of patients with osteochondritis dissecans of the capitellum is determined by the viability, stability, and size of the osteochondritis dissecans fragment. Conservative treatment should be reserved for individuals with stable and viable osteochondritis dissecans fragments and consists of activity modification and muscle strengthening exercises. Approximately 50% of early osteochondritis dissecans lesions with stable and viable fragments will heal with nonoperative therapy [47]. Surgical intervention is indicated for individuals who do not respond to initial conservative treatment and for individuals with unstable and nonviable osteochondritis dissecans fragments. Surgical intervention usually consists of debridement of the osteochondral dissecans fragment and drilling or microfracture of the adjacent subchondral bone. Internal stabilization of an acute osteochondritis dissecan lesion consisting of a single large fragment may be performed using bioabsorbable or metallic implants. Osteochondral autograft transplantation should be considered in patients with large osteochondritis dissecans lesions associated with extensive loss of the subchondral bone of the capitellum [48]. Most patients treated surgically for osteochondritis dissecans of the capitellum show at least some degree of initial improvement of their symptoms [53, 54, 55]; however, more than half of these individuals experience persistent elbow pain on long-term follow-up evaluation [56, 57].

Sports-related osseous injuries

Stress injury to the olecranon process of the proximal ulna has been described in professional baseball players and world-class javelin throwers. Prolonged exposure to the repetitive stress of throwing may result in tensile failure of the trabecular bone of the posterior medial aspect of the olecranon process. This injury is relatively uncommon and usually occurs in athletes with intact ulnar collateral ligaments. Patients present with posterior medial elbow pain which is most severe in the acceleration and follow-through phases of the throwing motion. Magnetic resonance imaging is useful in the early detection of stress injury to the proximal ulna before the development of a complete fracture though the olecranon process. Poorly defined patchy areas of bone marrow edema are noted on T1-weighted and T2-weighted images within the subcortical region of the posterior medial aspect of the proximal ulna (Fig. 16). Patients usually respond well to conservative treatment consisting of activity modification and muscle strengthening exercises [58, 59, 60].

Fig. 16
figure 16

Stress injury of the proximal ulnar in a professional male baseball pitcher with posteromedial elbow pain. Short-tau inversion recovery image of elbow shows mild, poorly defined edema (arrow) along the posteromedial superior aspect of the olecranon process of the proximal ulna. (Reprinted with permission from [58])

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Trauma

Magnetic resonance imaging is helpful in detecting radiographically occult fractures of the elbow in both children and adults (Fig. 17). Multiple studies have described the magnetic resonance imaging findings of patients with traumatic elbow joint effusions and no radiographically identifiable fracture. In children, magnetic resonance imaging detected occult fractures in 22–57% and soft tissue injuries in 62% of patients with traumatic elbow joint effusions [61, 62]. In adults, magnetic resonance imaging detected occult fractures in 47–100% and soft tissue injuries in 16–24% of patients with traumatic elbow joint effusions [62, 63]. Most individuals in these studies who did not have occult fractures had post-traumatic bone marrow contusions of the osseous structures of the elbow [61, 62, 63]. The ability of magnetic resonance imaging to detect radiographically occult fractures and soft tissue injuries in patients with traumatic elbow joint effusions appears to be only clinically significant in the adult population. The detection of occult fractures and soft tissue injuries in children has not been shown to influence the treatment of these individuals. All children with occult fractures or soft tissue injuries of the elbow detected by magnetic resonance imaging were successfully treated conservatively with a posterior splint [61, 62, 63, 64]; however, the detection of occult fractures or soft tissue injuries resulted in surgical treatment in 2 of 6 adult patients in one study [62].

Fig. 17
figure 17

Occult fracture of the elbow in a 30-year-old man with diffuse elbow pain following trauma. A Radial head X-ray view of the elbow shows no abnormality. B Fat-suppressed T2-weighted fast spin-echo image of the elbow shows diffuse bone marrow edema within the radial head and neck (arrowhead). C Axial T1-weighted spin-echo image of the elbow shows a low signal intensity fracture line through the radial neck (arrowhead).

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Magnetic resonance imaging is also useful in children to further evaluate elbow fractures which are detected on plain film radiographs. Most physeal injuries of the distal humerus occur between the ages of 4 and 8 years when the ossification centers of the distal humerus are poorly visualized on plain film radiographs [65]. It is often difficult to distinguish between Salter-Harris type-II fractures and Salter Harris type-IV fractures of the distal humerus on elbow radiographs in young children. Magnetic resonance imaging can be used to further evaluate physeal fractures of the distal humerus and to detect extension of these fractures into the articular surface of the elbow joint. In addition, the multiplanar capability of magnetic resonance imaging can determine the degree of articular surface displacement of fractures involving the epiphysis of the distal humerus and proximal ulna (Fig. 18) [66, 67]. The ability of magnetic resonance imaging to further evaluate pediatric elbow fractures is clinically significant and can lead to a change in the management of the patient. Salter-Harris type-II fractures of the distal humerus and nondisplaced fractures involving the epiphysis of the distal humerus and proximal ulna can be treated with closed reduction and cast immobilization; however, fractures involving the epiphysis of the distal humerus and proximal ulna require open reduction and internal fixation if there is more than 2 mm of displacement of the articular surface [65, 68].

Fig. 18
figure 18

Fracture of the proximal ulna in a 10-year-old boy with diffuse elbow pain following trauma. A Lateral X-ray view of elbow shows an oblique fracture through the olecranon process (arrow) which appears to extend into the articular surface of the proximal ulna (arrowhead). B Sagittal fat-suppressed proton-density spin-echo image of the elbow better demonstrates the intra-articular fracture of the proximal ulna (arrow). Note that there is no significant displacement of the articular surface of the proximal ulna (arrowhead)

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