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Sports injuries of the elbow
Magn Reson Imaging Clin N Am 11 (2003) 239–253
Sports injuries of the elbow Christine B. Chung, MD*, Hyun-Jin Kim, MD Department of Radiology, University of California San Diego and Veterans Affairs Healthcare System, 3350 La Jolla Village Drive, La Jolla, CA 92161, USA
The elbow is a complex joint comprised of three components: the humeroradial, humeroulnar, and proximal radioulnar articulations. As is often the case in the architecture of the body, structural complexity parallels functional complexity. In the elbow, though the primary motion of flexion and extension explains its designation as a hinge joint, it also is capable of axial rotation. Perhaps most importantly, the elbow serves as the functional link between the glenohumeral joint and the hand, facilitating remarkable accessibility of the fine motor and sensory abilities of the hand and fingers for the performance of the activities of daily living so commonly take for granted. Elbow injuries in the athlete are common and can be classified into acute or chronic injuries. The following discussion of sports injuries of the elbow will address the complex anatomy of the elbow, variations in normal anatomy that represent pitfalls in imaging diagnosis, and commonly encountered osseous and soft tissue pathology. Osseous anatomy and pathology The elbow articulation is comprised of three osseous (distal humerus, proximal ulna, and radius) structures that fit together like the pieces of a three-dimensional jigsaw puzzle to form three articulations. At the distal aspect of the humerus, the bone widens into a fanlike configuration. The medial most extent, the medial epicondyle, is an osseous projection that serves as the attachment site for the superficial flexor group of the forearm
* Corresponding author. E-mail address: [email protected] (C. Chung).
and the ulnar collateral ligament complex. The lateral epicondyle is the osseous projection that serves as the attachment site for the superficial extensor muscles of the forearm and parts of the radial collateral ligament complex. The medial third of the humeral articular surface is referred to as the trochlea, is intimate with the ulna, and forms the humeroulnar articulation. The lateral articulating surface of the humerus is formed by the capitellum, a smooth, rounded prominence that arises from its anterior and inferior surfaces. From its anterior margin with the distal humeral shaft, the capitellum curves downward and posteriorly. As it does so, its width decreases from anterior to posterior. This morphology of the capitellum (smooth surface), in conjunction with the knowledge that the adjacent lateral epicondyle (rough surface) is a posteriorly oriented osseous projection of the distal humerus, explains the pseudodefect of the capitellum (Fig. 1) [1]. The pseudodefect is encountered in coronal MR images, when an apparent interruption in the capitellar surface occurs at the posterior aspect of the joint. This appearance can be mistaken for an osteochondral lesion of the capitellum when it is simply the junction between the anterolateral capitellum and posterolateral lateral epicondyle. The articular surface of the proximal ulna is formed by the combination of the posterior olecranon and the anterior coranoid processes with the articular surfaces taking the configuration of a figure of eight. At the waist of the eight, or junction between anterior and posterior aspects of the ulna, the articular surface is traversed by a cartilage-free bony ridge (Fig. 2). This trochlear ridge is 2 to 3 mm wide and is at the same height as the adjacent cartilaginous surface, resulting in
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Fig. 1. (A) Coronal T1-weighted MR image of the elbow demonstrated irregular contour (arrow) in the region of the capitellum. (B) Corresponding sagittal T1-weighted MR image verifies the coronal image was obtained at the junction of the anterior capitellum and the posterior lateral epicondyle (arrow), the pseudodefect of the capitellum.
no impediment to smooth motion of the joint [2]. Knowledge of this anatomic detail avoids the mistaken diagnosis of central osteophyte formation, or articular surface irregularity on sagittal MR images of the elbow. The figure-of-eight morphology of the ulnar articular surface results in an additional imaging pitfall in diagnosis that of the trochlear groove (Fig 3). The waist of the figure of eight is formed by the tapered central surfaces of the coronoid and olecranon processes medially and laterally, forming small cortical notches devoid of cartilage. On sagittal MR images, these focal regions devoid of cartilage could be mistaken for a focal chondral lesion [2]. The proximal end of the radius consists of head, neck, and tuberosity. The radial head is shaped like a mortar with a cupped articular surface. The neck is the constricted portion of the bone distal to the articular surface. The tuberosity is beneath the medial aspect of the neck and serves as the attachment site for the biceps tendon.
Osteochondral lesions In the case of acute medial elbow injury, the involvement of a valgus force is usually described as one of the most common mechanisms of injury [3]. Subchondral bone and cartilage injuries that occur in this setting result from impaction and shearing forces applied to the articular surfaces (Fig. 4). The overall configuration of the humeroradial articulation, in this case, can be likened to a mortar and pestle with the capitellar articular surface impacting that of the radius to result in a chondral or osteochondral lesion of the capitellar surface. These acute posttraumatic lesions are manifested on MR images as irregularity of the chondral surface, disruption or irregularity of the subchondral bone plate, or the presence of a fracture line (Fig. 5). The acuity of the lesion and posttraumatic etiology are implied by the presence of marrow edema and joint effusion. Close inspection of the location of the lesion on coronal and sagittal MR images is of the utmost
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Fig. 2. A gross anatomic section in the sagittal plane obtained through the midportion of the ulnar articular surface demonstrates a focal area (arrow) between the coronoid articular surface (Co) and the olecranon articular surface (Ol) devoid of cartilage. This region is called the trochlear ridge and should not be mistaken for a central osteophyte.
importance to distinguish a true osteochondral lesion from the pseudodefect of the capitellum. Correlation with presenting clinical history is also helpful in determining the etiology of imaging findings. The entity of osteochondritis dissecans remains controversial, primarily because of debate over its etiology. The precise relationship of osteochondritis dissecans and an osteochondral fracture is unclear, but many investigators regard the former as a posttraumatic abnormality that may lead to osteonecrosis. Osteochondritis dissecans is believed to occur in immature athletes between 11 and 15 years of age, rarely in adults [4]. Osteochondritis dissecans of the elbow involves primarily the capitellum, but reports have described this process in the radius and trochlea [5]. Regardless of the etiology of the osteochondral injury, the role of imaging is to provide information regarding the integrity of the overlying articular cartilage, the viability of the separated fragment, and the presence of associated intraarticular bodies. CT and MR imaging with and without arthrography can provide this information to varying degrees, although no scientific investigation has been performed to date that establishes specific indications for each study. MR imaging, with its excellent soft tissue contrast, can directly visualize the articular cartilage and the character of the interface of the osteochondral lesion with native bone. The presence of joint fluid or granulation tissue at this interface, manifested as increased signal intensity on fluid-
Fig. 3. This sagittal MR arthrogram image in a cadaveric specimen at the margin of the ulnar articular surface demonstrates a focal area (arrow) between the coronoid articular surface (Co) and the olecranon articular surface (Ol) devoid of cartilage that is referred to as the trochlear groove. This normal anatomic appearance can be easily confused with an osteochondral lesion.
sensitive MR images, generally indicates an unstable lesion. The introduction of contrast into the articulation in conjunction with MR imaging can be helpful in two ways: (1) to facilitate the identification of intraarticular bodies (Fig. 6) and (2) to establish communication of the bonefragment interface with the articulation by following the route of contrast, providing even stronger evidence for an unstable fragment [6,7].
Capsule anatomy and pathology The osseous structures of the elbow are invested in a two-layer capsule. The synovial capsule or membrane comprises the deep layer and lines the more superficial fibrous capsule and the annular ligament. The fat pads of the elbow are located between the synovial and fibrous capsules.
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In addition, if viewed en face in the sagittal imaging plane, it could be misdiagnosed as an intraarticular body. The second variation in elbow anatomy that occurs in the elbow articulation is that of the plica. As previously mentioned, plica are believed to be the remnants of embryonic septae. These structures can become inflamed and thickened, resulting in impingement, snapping, and the sensation of intraarticular bodies. The diagnosis of a painful snapping plica can be confirmed if the plica snaps back and forward over the radial head in flexion and extension. This entity is often associated with focal areas of synovitis and cartilage lesions in the radial head [9]. The most common location for an abnormal plica is in the posterolateral joint space (Fig. 8) [10].
Ligament anatomy and pathology
Fig. 4. This diagram demonstrates the shearing and compressive forces associated with a valgus stress at the elbow. The compression at the humeroradial articulation can result in osteochondral injury to the capitellar articular surface and radial head or neck fractures. Compression at the lateral elbow results in opening of the medial joint space and potential insufficiency of the medial supporting structures (capsule, ulnar collateral ligament complex, and common flexor tendon).
As there are normal variations in osseous anatomy that can simulate pathology for the inexperienced reader, so there are similar variations in capsular anatomy. One such variation is a tongue of synovial tissue that projects into the joint between the radius and ulna, partially dividing the articulation into humeroulnar and humeroradial portions (Fig. 7). This has been referred to as the synovial fold [8]. Embryologically, the elbow joint space is formed by mesenchymal cavitations in three regions (humeroradial, humeroulnar, and proximal radioulnar) that ultimately become confluent. The synovial fringe is believed to be a septal remnant, or incomplete plica [8]. It can become compressed between the radial head and the humerus, resulting in pain and inflammation.
Classic descriptions of the ligamentous anatomy of the elbow emphasized radial and ulnar collateral ligaments, characterized as regions of focal thickening of the fibrous capsule that served to reinforce and stabilize the joint. Though the characterization and function of the ligaments has remained constant in the literature, the concept of their exact structural designation has become more complex [11]. Ulnar collateral ligament complex The medial collateral ligament of the elbow is comprised of three components, an anterior, posterior, and transverse bundle. The ligament originates from the central 65% of the anteroinferior surface of the medial epicondyle. The anterior band is taut from full extension to 60 degrees of flexion, whereas the posterior component is taut from 60 to 120 degrees of flexion. The anterior band is the strongest and stiffest component of the medial or ulnar collateral ligament complex. Its distal attachment is to the most medial portion of the coronoid process, also called the sublime tubercle, in close proximity to the attachment of the anterior capsule and brachialis tendon. The posterior bundle of the medial collateral ligament is a less discrete structure or thickening of the posterior elbow capsule and attaches in a broad fashion along the periphery of the medial ulna. The transverse bundle, also known as Cooper’s ligament, is comprised of fibers that bridge the base of the anterior and posterior bundles of the ligament complex.
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Fig. 5. (A) Coronal fat-suppressed T2-weighted fast spin echo MR image of the elbow demonstrates irregularity of the capitellar articular surface with bone marrow edema in the capitellum (arrow) and in the radial head (curved arrow). (B) Corresponding fat-suppressed T2-weighted fast spin echo MR image verifies the anterior articular location of the findings. The location, in conjunction with the bone marrow edema in the radius, suggests a posttraumatic etiology to this abnormality.
Valgus instability The principle function of the ulnar collateral ligament complex is to maintain medial joint stability to valgus stress. The anterior bundle is the most important component of the ligamentous complex to this end, as it serves as the primary medial stabilizer of the elbow from 30 to 120 degrees of flexion. The most common mechanisms of ulnar collateral ligament insufficiency are chronic attenuation, as seen in overhead or throwing athletes, and posttraumatic, usually after a fall on the outstretched arm. In the case of the latter, an acute tear of the ulnar collateral (Fig. 9) may be encountered. With throwing sports, high valgus stresses are placed on the medial aspect of the elbow. The maximum stress on the ulnar collateral ligament occurs during the late cocking and acceleration phases of throwing [12]. Repetitive insults to the ligament allow microscopic tears that progress to
significant attenuation or frank tearing within its substance. Though MR imaging allows direct visualization of the ligament complex, in chronic cases, the development of heterotopic calcification along the course of the ligament has been described [13]. Valgus instability is examined with the patient seated and his or her hand and forearm secured between the examiner’s torso and arm. The patient’s elbow is flexed to 25 degrees to unlock the olecranon process from its fossa, and the medial collateral ligament is palpated while a valgus stress is applied. Studies have shown that acquired valgus laxity does not exist in asymptomatic athletes, and that furthermore, there is no threshold value of measurement indicated for the diagnosis of acquired valgus laxity [14]. Treatment for ulnar collateral ligament injury in the throwing athlete includes rest with cessation of throwing, physical therapy with muscle strengthening, and nonsteroidal antiinflammatories.
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Fig. 6. Sagittal MR arthrogram image in a 34-year-old patient with a history of locking elbow shows a large intraarticular body (arrow) in the coronoid fossa outlined by contrast material.
Operative repair is typically reserved for competitive athletes or those involved in heavy manual labor because valgus laxity has been shown to cause minimal functional impairment in normal activities of daily living [11].
Fig. 7. Gross anatomic specimen oriented in the coronal plane in the region of the humeroradial articulation demonstrates a tongue of synovial tissue (arrow), the synovial fold, extending between the radial and the capitellar articular surfaces.
The annular ligament is circular in shape and extends around the radial head neck junction to attach at the anterior and posterior margins of the radial notch of the ulna. It serves as a restraining ligament, maintaining the radial head in contact
Radial collateral ligament complex Similar to the medial side of the elbow, on the lateral side, a radial collateral ligament complex is present. The radial, or lateral, collateral ligament complex consists of four components: radial collateral ligament, annular ligament, lateral ulnar collateral ligament, and accessory lateral collateral ligament. The radial collateral ligament is less distinct and more variable than its counterpart on the medial side. It is a thick, rough, triangular band of fibrous tissue that attaches superiorly to the lateral epicondyle of the humerus, beneath the origin of the common extensor tendon and inferiorly to the annular ligament. This ligament remains taut through the normal range of flexion and extension of the elbow.
Fig. 8. Gross anatomic specimen oriented in the axial plane shows a fold of synovial tissue (arrow), the posterior plica, extending into the posterolateral joint space.
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Fig. 10. Coronal MR arthrogram image in a 40-year-old patient demonstrates the normal appearance and course of the lateral ulnar collateral ligament (arrows). It extends from the undersurface of the lateral epicondyle and around the posterior head neck junction of the radius as it courses distally to its insertion on the supinator crest of the ulna.
Fig. 9. Coronal inversion recovery MR image in a 27year-old patient shows abnormal signal intensity and morphology of the ulnar collateral ligament. There is focal discontinuity of the ligament just distal to the humeral attachment consistent with a full thickness tear.
with the ulna and preventing inferior displacement of the radius. The lateral ulnar collateral ligament originates from the lateral epicondyle and blends with the fibers of the annular ligament proximally. It extends posteriorly to cradle the head–neck junction of the radius as it moves to its distal attachment at the supinator crest of the ulna (Fig. 10). This structure is one of the primary stabilizers of the elbow and is taut in flexion and extension. The accessory lateral collateral ligament is not uniformly present but represents discrete fibers that extend from the annular ligament to the supinator crest. When present, it may serve to stabilize the annular ligament during varus stress. Varus instability Lateral elbow instability related to isolated abnormalities of the lateral collateral ligament complex is not as well described as that on the medial side of the elbow. If it were to occur, the
mechanism would be a stress or force applied to the medial side of the articulation, resulting in compression on that side, with opening of the lateral articulation and subsequent insufficiency of the radial collateral ligament (Figs. 11, 12). As the radial collateral ligament attaches on and is intimately associated with the annular ligament, an abnormality discovered in one of the structures requires careful inspection of the other. Varus stress applied to the elbow may occur as an acute injury, but rarely as a repetitive stress as encountered on the medial side. Though lateral collateral ligament injuries rarely occur as the result of an isolated varus stress, other causes can commonly result in this injury, including dislocation, subluxation and overly aggressive surgery (release of the common extensor tendon or radial head resection). Varus instability is also tested with the elbow in full extension and 30 degrees of flexion to unlock the olecranon. A varus stress is applied to the elbow while palpating the lateral joint line. Posterolateral rotary instability and elbow dislocation The subject of elbow instability is complex and has been a challenge because of the difficulty establishing a mechanism of injury and reliable clinical tests for diagnosis. With the realization that elbow instability is more common than previously thought, marked advances in the understanding of this entity are occurring.
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Fig. 11. This diagram demonstrates the shearing and compressive forces associated with a varus stress at the elbow. The compression at the medial elbow results in opening of the lateral joint space, and potential insufficiency of the lateral supporting structures (capsule, radial collateral ligament complex, and common extensor tendon).
A simple classification for elbow instability does not exist. The literature points to five criteria that should be considered to produce a useful classification system for treatment: (1) timing (acute, chronic, recurrent), (2) articulation involved (elbow versus radial head), (3) direction of displacement (valgus, varus, anterior, posterolateral rotary), (4) degree of displacement (subluxation or dislocation), and (5) presence or absence of associated fractures [15]. For recurrent instability, posterolateral rotary instability is the most common pattern. This type of instability represents a spectrum of pathology consisting of three stages according to the degree of soft tissue disruption. In stage 1, there is posterolateral subluxation of the ulna on the humerus that results in insufficiency of the lateral ulnar collateral ligament (Fig. 13) [15–17]. In stage 2, the elbow dislocates incompletely so that the coronoid is
perched under the trochlea. In this stage, the radial collateral ligament, and anterior and posterior portions of the capsule, are disrupted in addition to the lateral ulnar collateral ligament. In stage 3, the elbow dislocates anteriorly so that the coronoid rests behind the humerus. Stage 3 is subclassified into three categories. In stage 3A, the anterior band of the medial collateral ligament is intact and the elbow is stable to valgus stress after reduction. In stage 3B, the anterior band of the medial collateral ligament is disrupted so that the elbow is unstable with valgus stress. In stage 3, the entire distal humerus is stripped of soft tissues, rendering the elbow grossly unstable even when a splint or cast is applied with the elbow in a semiflexed position. This classification system is helpful because each stage has specific clinical, radiographic, and pathologic features that are predictable and have implications for treatment [15]. Traditional teaching dictated that the mechanism of injury for elbow dislocation included hyperextension. More recently, it is believed that this mechanism is the result of a fall on the outstretched hand. The elbow experiences an axial compressive force during flexion as the body approaches the ground. As the body rotates internally on the elbow (forearm rotates externally on the humerus), a supination moment occurs at the elbow. This combination of valgus and supination with axial compression during flexion results in the posterolateral rotary subluxation or dislocation of the elbow. The corresponding pathoanatomy previously described can be thought of simply as the disruption of a soft tissue ring that progresses from posterolateral to medial in three stages [15]. Subluxation or dislocation of the elbow can be associated with fractures. Fracture dislocations most commonly involve the coronoid and radial head, a constellation of findings referred to as the ‘‘terrible triad’’ of the elbow because the injury complex is difficult to treat and prone to unsatisfactory results [15]. Radial head fractures do not cause clinically significant instability unless the medial collateral ligament is disrupted. An important feature of elbow injuries to recognize is that the small flake fracture of the coronoid, commonly seen in elbow dislocations, is not an avulsion fracture. Nothing attaches to the tip of the coronoid, rather the capsule attaches on the downward slope of the coronoid, the brachialis even more distal. This fracture is a shear fracture and is likely pathognomonic of an episode of elbow subluxation or dislocation (Fig. 14).
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Fig. 12. (A) Coronal T1-weighted MR image of the elbow in a 47-year-old man shows discontinuity of the radial collateral ligament (arrow) at the humeral attachment. The ligament also demonstrates somewhat abnormal morphology with thickening. The overlying common extensor tendon is normal. (B) Corresponding axial fat-suppressed proton density weighted MR image shows abnormal morphology and signal intensity (arrow) of the posterior attachment of the annular ligament, consistent with a high-grade partial tear.
A second consideration with respect to elbow dislocation is that as the ring of soft tissues is disrupted from posterolateral to medial, the capsule is torn and insufficient. In the absence of an intact capsule, joint fluid dissects through the soft tissue planes of the forearm, negating an indirect radiographic sign of trauma in the elbow, that of the joint effusion. Tendon anatomy and pathology The many muscles about the elbow can be divided into four groups: posterior, anterior, medial, and lateral. The muscles of the posterior group are the triceps and anconeus. The muscles of the anterior group are the biceps brachii and brachialis. The muscles in the medial group are the pronator teres, the palmaris longus, and the flexors of the hand and wrist. The muscles in the lateral group include the supinator, brachioradialis, and extensor muscles of the hand and wrist. Specific anatomic considerations and tendon
pathology commonly encountered in the elbow will be addressed. The classification of tendon injuries about the elbow can be organized by location, acuity, and degree of injury. Tendon injury related to a single isolated event is uncommon, although exceptions to this rule do occur. More commonly, tendinous injuries in this location relate to chronic repetitive microtrauma. MR imaging, with its excellent soft tissue contrast, is particularly well suited to diagnose tendon pathology. This is done primarily by close inspection of signal intensity and morphology of the tendons. As elsewhere in the body, the tendons about the elbow should be smooth, linear structures of low signal intensity. Abnormal morphology (attenuation or thickening) can be seen in tendinosis or tear. If signal intensity becomes bright or increased on fluid sensitive sequences within the substance of a tendon, a tear is present. Tears can be further characterized as partial or complete. A complete tear is diagnosed by a focal area of discontinuity.
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Fig. 13. Inversion recovery coronal MR image of the elbow in a 52-year-old man shows abnormal high signal intensity (arrows) in the expected position of the lateral ulnar collateral ligament, with no visualization of a normal ligament.
Common flexor tendon and medial muscles The muscular anatomy about the medial elbow is complex and includes three separate layers. The most superficial layer includes the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. The middle layer is comprised of the flexor digitorum superficialis, and the deep layer is made up of the flexor digitorum profundus. Only the flexor digitorum profundus does not take a part of its origin from the common flexor tendon. In rare cases, it may be necessary to localize pathology to a specific muscle group; however, the majority of pathology will occur in the common flexor tendon near its distal humeral attachment. Common extensor tendon and lateral muscles The lateral extensor muscles include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles. Only
Fig. 14. Sagittal fat-suppressed proton density weighted MR image demonstrates several findings of acute dislocation: (1) anterior subluxation of the humerus, (2) coronoid process fracture (arrow), (3) irregularity of the articular surface of the olecranon (curved arrow), and (4) disruption of the anterior and posterior capsule (double arrow). The corresponding coronal image (not shown here) further demonstrated complete disruption of the radial and ulnar collateral ligament complexes.
the extensor carpi radialis longus does not take a part of its origin from the common extensor tendon. As with the medial muscles, the vast majority of pathology encountered in this region is associated with the common extensor tendon rather than specific muscles. Epicondylitis and overuse syndromes Chronic stress applied to the elbow is the most frequent injury in athletes, and a spectrum of pathology can exist with varying degrees of severity. The frequency of involvement of the common flexor and extensor tendons to the medial and lateral epicondyles, respectively, has led to the designation of ‘‘epicondylitis’’ as a general term applied to these overuse syndromes. Anatomically, these overuse syndromes are classified by location and are further associated with sports that incite
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the pathology. The injury is believed to result from extrinsic tensile overload of the tendon, which, over time, produces microscopic tears that do not heal appropriately. Although these overuse entities about the elbow have been termed ‘‘epicondylitis’’ for the purpose of clinical diagnosis, inflammatory osseous changes rarely occur. The imaging findings are those reflecting chronic change in the tendon as evidenced by tendinosis alone or in conjunction with partial or complete tear. The distinction between types of pathology is made by consideration of morphology and signal intensity changes. Medial epicondylitis involves pathology of the common flexor tendon and is associated primarily with the sport of golfing. It also has been reported with javelin throwers, racquetball and squash players, swimmers, and bowlers. The pronator teres and flexor carpi radialis tendons are involved most frequently resulting in pain and tenderness to palpation over the anterior aspect of the medial epicondyle of the humerus and origin of the common flexor tendon. The mechanism of injury
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includes repetitive valgus strain with pain resulting from resisting pronation of the forearm or flexion of the wrist [18]. The imaging findings encountered can include tendinosis or tendinosis with superimposed partial or full thickness tear (Fig. 15). When assessing the tendon, it is necessary to closely scrutinize the underlying ulnar collateral ligament complex to ensure integrity. Lateral epicondylitis is the most common problem in the elbow in athletes and has been termed ‘‘tennis elbow.’’ This term may be somewhat inappropriate as 95% of cases of the clinical entity of lateral epicondylitis occur in non–tennis players [18]. Moreover, it has been estimated that 50% of people partaking in any sport with overhead arm motion will develop this process [19]. Lateral epicondylitis is associated with repetitive and excessive use of the wrist extensors. The pathology most commonly affects the extensor carpi radialis brevis at the common extensor tendon (Fig. 16). A number of investigators have described the pathology encountered in the
Fig. 15. (A) Frontal view of the elbow shows subtle irregularity (arrow) of the medial aspect of the distal humerus. (B) Coronal fat-suppressed T2-weighted fast spin echo image shows a focal full-thickness tear (arrow) of the attachment of the common flexor tendon to the medial epicondyle.
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Biceps tendon The biceps brachii muscle consists of two heads, the short head and long head. The short head arises from the tip of the coracoid process, in common with the coracobrachialis. The long head arises from the supraglenoid tubercle of the scapula. The two muscles join to form a common tendon 6 to 7 cm above the elbow joint line. This common tendon traverses the antecubital fossa to dive to its attachment at the radial tuberosity. An aponeurosis, the bicipital aponeurosis or lacertus fibrosus, arises from the musculotendinous junction, passes across the brachial artery, and merges with the fascia that covers the pronator teres and superficial flexors of the forearm. The distal biceps tendon does not have a tendon sheath, rather there is a bursa (cubital bursa) intimately associated with its attachment to the radial tuberosity [24]. Distal biceps tendon rupture
Fig. 16. Coronal fat-suppressed T2-weighted fast spin echo image of the elbow in a 50-year-old tennis player demonstrates abnormal morphology of the common extensor tendon with superimposed intrasubstance high signal intensity (arrow) consistent with a partial tear of the tendon. These imaging findings support the clinical diagnosis of tennis elbow.
degenerated tendon of this disease process. Histologically, necrosis, round cell infiltration, focal calcification, and scar formation have been shown [20]. In addition, invasion of blood vessels, fibroblastic proliferation, and lymphatic infiltration, the combination of which are referred to as angiofibroblastic hyperplasia, occur and ultimately lead to mucoid degeneration as the process continues [21,22]. The absence of a significant inflammatory response has been emphasized repeatedly and may explain the inadequacy of the healing process. The imaging findings in this process are exactly those encountered in the clinical entity of medial epicondylitis. As on the medial side, when pathology is encountered in the tendon, close scrutiny of the underlying ligamentous complex is necessary to exclude concomitant injury. In particular, thickening and tears of the lateral ulnar collateral ligament have been encountered with lateral epicondylitis [23].
Rupture of the tendon of the biceps brachii muscle at the elbow is rare, and constitutes less than 5% of all biceps tendon injuries [25]. It usually occurs in the dominant arm of males. Injuries to the musculotendinous junction have been reported, but the most common injury is complete avulsion of the tendon from the radial tuberosity. Although the injury often occurs acutely after a single traumatic event, the failure is thought to be the result of preexisting changes in the distal biceps tendon caused by intrinsic tendon degeneration, enthesopathy at the radial tuberosity, or cubital bursal changes. The typical mechanism of injury relates to forceful hyperextension applied to a flexed and supinated forearm. Athletes involved in strength sports, such as competitive weightlifting, football, and rugby, often sustain this injury. Clinically the patient gives a history of feeling a ‘‘pop’’ or sudden sharp pain in the antecubital fossa. The classic presentation of a complete distal biceps rupture is that of a mass in the antecubital fossa caused by proximal migration of the biceps muscle belly. Accurate diagnosis is more difficult in cases of the rare partial tear of the tendon, or more common complete tear of the tendon without retraction. The latter case can occur with an intact bicipital aponeurosis, which serves to tether the ruptured tendon to the pronator flexor muscle group (Fig. 17). MR imaging diagnosis of biceps tendon pathology becomes important in patients who do not present with the classic history or mass in the antecubital fossa, or for evaluation of the integrity
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Fig. 17. (A) Axial T1-weighted MR image shows abnormal morphology of the distal biceps tendon (arrow). The thickened lacertus fibrosus is intact (curved arrow). (B) Oblique coronal fat-suppressed T2-weighted MR image demonstrates a small stump of residual tendon (arrow) coursing toward the radial tuberosity. The high signal intensity around the tendon remnant is fluid within the cubital bursa.
of the lacertus fibrosus. MR imaging diagnosis of tendon pathology, as previously mentioned, is largely dependent on morphology, signal intensity, and the identification of areas of tendon discontinuity. In the case of the biceps tendon, an important indirect sign of tendon pathology is the presence of cubital bursitis (Fig. 17). With delayed diagnosis, chronic pain can ensue, as well as weakness in flexion, supination, and with grip strength. Treatment options favor surgical reattachment because nonoperatively treated ruptures have been reported to result in loss of 20% of elbow flexion strength and 40% of supination strength. If operative treatment is chosen, early repair is desirable, particularly when the lacertus fibrosus is ruptured and there is muscle retraction. If the lacertus fibrosus is intact, delayed primary repair is feasible [25]. Triceps tendon The triceps consists of three muscle bellies: the long head, the lateral head, and the medial head. The long head of the triceps arises by a strong
tendon from the infraglenoid tubercle of the scapula near the inferior margin of the glenoid cavity. It descends into the arm between the teres major and teres minor muscles. The lateral head originates from the posterior and lateral surfaces of the humerus and from the lateral intermuscular septum. The medial head arises from the posterior surface of the humerus, medial and below the radial groove, and from the medial and lower part of the lateral intermuscular septum. The tendon of the triceps descends to attach to the upper surface of the olecranon process of the ulna and to the antebrachial fascia near the laterally located anconeus muscle and tendon. Rupture of the triceps tendon is rare. The mechanism of injury has been reported to result from a direct blow to the triceps insertion or a deceleration force applied to the extended arm with contraction of the triceps as in a fall. Similar to pathology encountered in the distal biceps tendon, most ruptures occur at the insertion site, although musculotendinous junction and muscle belly injuries have been reported. Complete
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ruptures are more common than partial tears. Associated findings may include olecranon bursitis, subluxation of the ulnar nerve, or fracture of the radial head. Accurate clinical diagnosis relies on the presence of local pain, swelling, ecchymosis, a palpable defect, and partial or complete loss of the ability to extend the elbow. With more than 2 cm of retraction between the origin and the insertion, a 40% loss of extension strength can result [25]. For MR imaging diagnosis of triceps tendon pathology, it is imperative to be aware that the triceps tendon appearance is largely dependent on arm position. The tendon will appear lax and redundant when imaged in full extension, whereas it is taut in flexion. MR imaging features of a tear are similar to those associated with any other tendon. The treatment of a complete rupture is surgical repair; partial tears are often treated conservatively.
Summary There is a wide spectrum of pathology that affects the elbow in the athlete. This is further complicated by the complex anatomy of this articulation and the numerous normal anatomic variations that can serve as pitfalls in imaging diagnosis. A detailed knowledge of the anatomy and pathology that commonly affect this articulation can facilitate the ease and accuracy of imaging diagnosis. References [1] Rosenberg ZS, Beltran J, Cheung YY. Pseudodefect of the capitellum: potential MR imaging pitfall. Radiology 1994;191(3):821–3. [2] Rosenberg ZS, Beltran J, Cheung Y, Broker M. MR imaging of the elbow: normal variant and potential diagnostic pitfalls of the trochlear groove and cubital tunnel. AJR Am J Roentgenol 1995; 164(2):415–8. [3] Pincivero DM, Heinrichs K, Perrin DH. Medial elbow stability. Clinical implications. Sports Med 1994;18(2):141–8. [4] Bradley JP, Petrie RS. Osteochondritis dissecans of the humeral capitellum. Diagnosis and treatment. Clin Sports Med 2001;20(3):565–90. [5] Patel N, Weiner SD. Osteochondritis dissecans involving the trochlea: report of two patients (three elbows) and review of the literature. J Pediatr Orthop 2002;22(1):48–51.
[6] Steinbach LS, Palmer WE, Schweitzer ME. Special focus session. MR arthrography. Radiographics 2002;22(5):1223–46. [7] Carrino JA, Smith DK, Schweitzer ME. MR arthrography of the elbow and wrist. Semin Musculoskelet Radiol 1998;2(4):397–414. [8] Clarke RP. Symptomatic, lateral synovial fringe (plica) of the elbow joint. Arthroscopy 1988;4(2): 112–6. [9] Antuna SA, O’Driscoll SW. Snapping plicae associated with radiocapitellar chondromalacia. Arthroscopy 2001;17(5):491–5. [10] Awaya H, Schweitzer ME, Feng SA, et al. Elbow synovial fold syndrome: MR imaging findings. AJR Am J Roentgenol 2001;177(6): 1377–81. [11] Cohen MS, Bruno RJ. The collateral ligaments of the elbow: anatomy and clinical correlation. Clin Orthop 2001;(383):123–30. [12] Phillips CS, Segalman KA. Diagnosis and treatment of post-traumatic medial and lateral elbow ligament incompetence. Hand Clin 2002;18(1):149–59. [13] Mulligan SA, Schwartz ML, Broussard MF, Andrews JR. Heterotopic calcification and tears of the ulnar collateral ligament: radiographic and MR imaging findings. AJR Am J Roentgenol 2000; 175(4):1099–102. [14] Singh H, Osbahr DC, Wickham MQ, et al. Valgus laxity of the ulnar collateral ligament of the elbow in collegiate athletes. Am J Sports Med 2001; 29(5):558–61. [15] O’Driscoll SW. Classification and evaluation of recurrent instability of the elbow. Clin Orthop 2000;(370):34–43. [16] Potter HG, Weiland AJ, Schatz JA, et al. Posterolateral rotatory instability of the elbow: usefulness of MR imaging in diagnosis. Radiology 1997; 204(1):185–9. [17] Dunning CE, Zarzour ZD, Patterson SD, et al. Ligamentous stabilizers against posterolateral rotatory instability of the elbow. J Bone Joint Surg Am 2001;83-A(12):1823–8. [18] Frostick SP, Mohammad M, Ritchie DA. Sport injuries of the elbow. Br J Sports Med 1999; 33(5):301–11. [19] Field LD, Savoie FH. Common elbow injuries in sport. Sports Med 1998;26(3):193–205. [20] Nirschl RP, Pettrone FA. Tennis elbow. The surgical treatment of lateral epicondylitis. J Bone Joint Surg Am 1979;61(6A):832–9. [21] Regan W, Wold LE, Coonrad R, Morrey BF. Microscopic histopathology of chronic refractory lateral epicondylitis. Am J Sports Med 1992; 20(6):746–9. [22] Nirschl RP. Elbow tendinosis/tennis elbow. Clin Sports Med 1992;11(4):851–70. [23] Bredella MA, Tirman PF, Fritz RC, et al. MR imaging findings of lateral ulnar collateral ligament abnormalities in patients with lateral
C.B. Chung, H.-J. Kim / Magn Reson Imaging Clin N Am 11 (2003) 239–253 epicondylitis. AJR Am J Roentgenol 1999;173(5): 1379–82. [24] Skaf AY, Boutin RD, Dantas RW, et al. Bicipitoradial bursitis: MR imaging findings in eight patients and anatomic data from contrast
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material opacification of bursae followed by routine radiography and MR imaging in cadavers. Radiology 1999;212(1):111–6. [25] Rettig AC. Traumatic elbow injuries in the athlete. Orthop Clin North Am 2002;33(3):509–22.
Sports injuries of the elbow Christine B. Chung, MD*, Hyun-Jin Kim, MD Department of Radiology, University of California San Diego and Veterans Affairs Healthcare System, 3350 La Jolla Village Drive, La Jolla, CA 92161, USA
The elbow is a complex joint comprised of three components: the humeroradial, humeroulnar, and proximal radioulnar articulations. As is often the case in the architecture of the body, structural complexity parallels functional complexity. In the elbow, though the primary motion of flexion and extension explains its designation as a hinge joint, it also is capable of axial rotation. Perhaps most importantly, the elbow serves as the functional link between the glenohumeral joint and the hand, facilitating remarkable accessibility of the fine motor and sensory abilities of the hand and fingers for the performance of the activities of daily living so commonly take for granted. Elbow injuries in the athlete are common and can be classified into acute or chronic injuries. The following discussion of sports injuries of the elbow will address the complex anatomy of the elbow, variations in normal anatomy that represent pitfalls in imaging diagnosis, and commonly encountered osseous and soft tissue pathology. Osseous anatomy and pathology The elbow articulation is comprised of three osseous (distal humerus, proximal ulna, and radius) structures that fit together like the pieces of a three-dimensional jigsaw puzzle to form three articulations. At the distal aspect of the humerus, the bone widens into a fanlike configuration. The medial most extent, the medial epicondyle, is an osseous projection that serves as the attachment site for the superficial flexor group of the forearm
* Corresponding author. E-mail address: [email protected] (C. Chung).
and the ulnar collateral ligament complex. The lateral epicondyle is the osseous projection that serves as the attachment site for the superficial extensor muscles of the forearm and parts of the radial collateral ligament complex. The medial third of the humeral articular surface is referred to as the trochlea, is intimate with the ulna, and forms the humeroulnar articulation. The lateral articulating surface of the humerus is formed by the capitellum, a smooth, rounded prominence that arises from its anterior and inferior surfaces. From its anterior margin with the distal humeral shaft, the capitellum curves downward and posteriorly. As it does so, its width decreases from anterior to posterior. This morphology of the capitellum (smooth surface), in conjunction with the knowledge that the adjacent lateral epicondyle (rough surface) is a posteriorly oriented osseous projection of the distal humerus, explains the pseudodefect of the capitellum (Fig. 1) [1]. The pseudodefect is encountered in coronal MR images, when an apparent interruption in the capitellar surface occurs at the posterior aspect of the joint. This appearance can be mistaken for an osteochondral lesion of the capitellum when it is simply the junction between the anterolateral capitellum and posterolateral lateral epicondyle. The articular surface of the proximal ulna is formed by the combination of the posterior olecranon and the anterior coranoid processes with the articular surfaces taking the configuration of a figure of eight. At the waist of the eight, or junction between anterior and posterior aspects of the ulna, the articular surface is traversed by a cartilage-free bony ridge (Fig. 2). This trochlear ridge is 2 to 3 mm wide and is at the same height as the adjacent cartilaginous surface, resulting in
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Fig. 1. (A) Coronal T1-weighted MR image of the elbow demonstrated irregular contour (arrow) in the region of the capitellum. (B) Corresponding sagittal T1-weighted MR image verifies the coronal image was obtained at the junction of the anterior capitellum and the posterior lateral epicondyle (arrow), the pseudodefect of the capitellum.
no impediment to smooth motion of the joint [2]. Knowledge of this anatomic detail avoids the mistaken diagnosis of central osteophyte formation, or articular surface irregularity on sagittal MR images of the elbow. The figure-of-eight morphology of the ulnar articular surface results in an additional imaging pitfall in diagnosis that of the trochlear groove (Fig 3). The waist of the figure of eight is formed by the tapered central surfaces of the coronoid and olecranon processes medially and laterally, forming small cortical notches devoid of cartilage. On sagittal MR images, these focal regions devoid of cartilage could be mistaken for a focal chondral lesion [2]. The proximal end of the radius consists of head, neck, and tuberosity. The radial head is shaped like a mortar with a cupped articular surface. The neck is the constricted portion of the bone distal to the articular surface. The tuberosity is beneath the medial aspect of the neck and serves as the attachment site for the biceps tendon.
Osteochondral lesions In the case of acute medial elbow injury, the involvement of a valgus force is usually described as one of the most common mechanisms of injury [3]. Subchondral bone and cartilage injuries that occur in this setting result from impaction and shearing forces applied to the articular surfaces (Fig. 4). The overall configuration of the humeroradial articulation, in this case, can be likened to a mortar and pestle with the capitellar articular surface impacting that of the radius to result in a chondral or osteochondral lesion of the capitellar surface. These acute posttraumatic lesions are manifested on MR images as irregularity of the chondral surface, disruption or irregularity of the subchondral bone plate, or the presence of a fracture line (Fig. 5). The acuity of the lesion and posttraumatic etiology are implied by the presence of marrow edema and joint effusion. Close inspection of the location of the lesion on coronal and sagittal MR images is of the utmost
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Fig. 2. A gross anatomic section in the sagittal plane obtained through the midportion of the ulnar articular surface demonstrates a focal area (arrow) between the coronoid articular surface (Co) and the olecranon articular surface (Ol) devoid of cartilage. This region is called the trochlear ridge and should not be mistaken for a central osteophyte.
importance to distinguish a true osteochondral lesion from the pseudodefect of the capitellum. Correlation with presenting clinical history is also helpful in determining the etiology of imaging findings. The entity of osteochondritis dissecans remains controversial, primarily because of debate over its etiology. The precise relationship of osteochondritis dissecans and an osteochondral fracture is unclear, but many investigators regard the former as a posttraumatic abnormality that may lead to osteonecrosis. Osteochondritis dissecans is believed to occur in immature athletes between 11 and 15 years of age, rarely in adults [4]. Osteochondritis dissecans of the elbow involves primarily the capitellum, but reports have described this process in the radius and trochlea [5]. Regardless of the etiology of the osteochondral injury, the role of imaging is to provide information regarding the integrity of the overlying articular cartilage, the viability of the separated fragment, and the presence of associated intraarticular bodies. CT and MR imaging with and without arthrography can provide this information to varying degrees, although no scientific investigation has been performed to date that establishes specific indications for each study. MR imaging, with its excellent soft tissue contrast, can directly visualize the articular cartilage and the character of the interface of the osteochondral lesion with native bone. The presence of joint fluid or granulation tissue at this interface, manifested as increased signal intensity on fluid-
Fig. 3. This sagittal MR arthrogram image in a cadaveric specimen at the margin of the ulnar articular surface demonstrates a focal area (arrow) between the coronoid articular surface (Co) and the olecranon articular surface (Ol) devoid of cartilage that is referred to as the trochlear groove. This normal anatomic appearance can be easily confused with an osteochondral lesion.
sensitive MR images, generally indicates an unstable lesion. The introduction of contrast into the articulation in conjunction with MR imaging can be helpful in two ways: (1) to facilitate the identification of intraarticular bodies (Fig. 6) and (2) to establish communication of the bonefragment interface with the articulation by following the route of contrast, providing even stronger evidence for an unstable fragment [6,7].
Capsule anatomy and pathology The osseous structures of the elbow are invested in a two-layer capsule. The synovial capsule or membrane comprises the deep layer and lines the more superficial fibrous capsule and the annular ligament. The fat pads of the elbow are located between the synovial and fibrous capsules.
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In addition, if viewed en face in the sagittal imaging plane, it could be misdiagnosed as an intraarticular body. The second variation in elbow anatomy that occurs in the elbow articulation is that of the plica. As previously mentioned, plica are believed to be the remnants of embryonic septae. These structures can become inflamed and thickened, resulting in impingement, snapping, and the sensation of intraarticular bodies. The diagnosis of a painful snapping plica can be confirmed if the plica snaps back and forward over the radial head in flexion and extension. This entity is often associated with focal areas of synovitis and cartilage lesions in the radial head [9]. The most common location for an abnormal plica is in the posterolateral joint space (Fig. 8) [10].
Ligament anatomy and pathology
Fig. 4. This diagram demonstrates the shearing and compressive forces associated with a valgus stress at the elbow. The compression at the humeroradial articulation can result in osteochondral injury to the capitellar articular surface and radial head or neck fractures. Compression at the lateral elbow results in opening of the medial joint space and potential insufficiency of the medial supporting structures (capsule, ulnar collateral ligament complex, and common flexor tendon).
As there are normal variations in osseous anatomy that can simulate pathology for the inexperienced reader, so there are similar variations in capsular anatomy. One such variation is a tongue of synovial tissue that projects into the joint between the radius and ulna, partially dividing the articulation into humeroulnar and humeroradial portions (Fig. 7). This has been referred to as the synovial fold [8]. Embryologically, the elbow joint space is formed by mesenchymal cavitations in three regions (humeroradial, humeroulnar, and proximal radioulnar) that ultimately become confluent. The synovial fringe is believed to be a septal remnant, or incomplete plica [8]. It can become compressed between the radial head and the humerus, resulting in pain and inflammation.
Classic descriptions of the ligamentous anatomy of the elbow emphasized radial and ulnar collateral ligaments, characterized as regions of focal thickening of the fibrous capsule that served to reinforce and stabilize the joint. Though the characterization and function of the ligaments has remained constant in the literature, the concept of their exact structural designation has become more complex [11]. Ulnar collateral ligament complex The medial collateral ligament of the elbow is comprised of three components, an anterior, posterior, and transverse bundle. The ligament originates from the central 65% of the anteroinferior surface of the medial epicondyle. The anterior band is taut from full extension to 60 degrees of flexion, whereas the posterior component is taut from 60 to 120 degrees of flexion. The anterior band is the strongest and stiffest component of the medial or ulnar collateral ligament complex. Its distal attachment is to the most medial portion of the coronoid process, also called the sublime tubercle, in close proximity to the attachment of the anterior capsule and brachialis tendon. The posterior bundle of the medial collateral ligament is a less discrete structure or thickening of the posterior elbow capsule and attaches in a broad fashion along the periphery of the medial ulna. The transverse bundle, also known as Cooper’s ligament, is comprised of fibers that bridge the base of the anterior and posterior bundles of the ligament complex.
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Fig. 5. (A) Coronal fat-suppressed T2-weighted fast spin echo MR image of the elbow demonstrates irregularity of the capitellar articular surface with bone marrow edema in the capitellum (arrow) and in the radial head (curved arrow). (B) Corresponding fat-suppressed T2-weighted fast spin echo MR image verifies the anterior articular location of the findings. The location, in conjunction with the bone marrow edema in the radius, suggests a posttraumatic etiology to this abnormality.
Valgus instability The principle function of the ulnar collateral ligament complex is to maintain medial joint stability to valgus stress. The anterior bundle is the most important component of the ligamentous complex to this end, as it serves as the primary medial stabilizer of the elbow from 30 to 120 degrees of flexion. The most common mechanisms of ulnar collateral ligament insufficiency are chronic attenuation, as seen in overhead or throwing athletes, and posttraumatic, usually after a fall on the outstretched arm. In the case of the latter, an acute tear of the ulnar collateral (Fig. 9) may be encountered. With throwing sports, high valgus stresses are placed on the medial aspect of the elbow. The maximum stress on the ulnar collateral ligament occurs during the late cocking and acceleration phases of throwing [12]. Repetitive insults to the ligament allow microscopic tears that progress to
significant attenuation or frank tearing within its substance. Though MR imaging allows direct visualization of the ligament complex, in chronic cases, the development of heterotopic calcification along the course of the ligament has been described [13]. Valgus instability is examined with the patient seated and his or her hand and forearm secured between the examiner’s torso and arm. The patient’s elbow is flexed to 25 degrees to unlock the olecranon process from its fossa, and the medial collateral ligament is palpated while a valgus stress is applied. Studies have shown that acquired valgus laxity does not exist in asymptomatic athletes, and that furthermore, there is no threshold value of measurement indicated for the diagnosis of acquired valgus laxity [14]. Treatment for ulnar collateral ligament injury in the throwing athlete includes rest with cessation of throwing, physical therapy with muscle strengthening, and nonsteroidal antiinflammatories.
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Fig. 6. Sagittal MR arthrogram image in a 34-year-old patient with a history of locking elbow shows a large intraarticular body (arrow) in the coronoid fossa outlined by contrast material.
Operative repair is typically reserved for competitive athletes or those involved in heavy manual labor because valgus laxity has been shown to cause minimal functional impairment in normal activities of daily living [11].
Fig. 7. Gross anatomic specimen oriented in the coronal plane in the region of the humeroradial articulation demonstrates a tongue of synovial tissue (arrow), the synovial fold, extending between the radial and the capitellar articular surfaces.
The annular ligament is circular in shape and extends around the radial head neck junction to attach at the anterior and posterior margins of the radial notch of the ulna. It serves as a restraining ligament, maintaining the radial head in contact
Radial collateral ligament complex Similar to the medial side of the elbow, on the lateral side, a radial collateral ligament complex is present. The radial, or lateral, collateral ligament complex consists of four components: radial collateral ligament, annular ligament, lateral ulnar collateral ligament, and accessory lateral collateral ligament. The radial collateral ligament is less distinct and more variable than its counterpart on the medial side. It is a thick, rough, triangular band of fibrous tissue that attaches superiorly to the lateral epicondyle of the humerus, beneath the origin of the common extensor tendon and inferiorly to the annular ligament. This ligament remains taut through the normal range of flexion and extension of the elbow.
Fig. 8. Gross anatomic specimen oriented in the axial plane shows a fold of synovial tissue (arrow), the posterior plica, extending into the posterolateral joint space.
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Fig. 10. Coronal MR arthrogram image in a 40-year-old patient demonstrates the normal appearance and course of the lateral ulnar collateral ligament (arrows). It extends from the undersurface of the lateral epicondyle and around the posterior head neck junction of the radius as it courses distally to its insertion on the supinator crest of the ulna.
Fig. 9. Coronal inversion recovery MR image in a 27year-old patient shows abnormal signal intensity and morphology of the ulnar collateral ligament. There is focal discontinuity of the ligament just distal to the humeral attachment consistent with a full thickness tear.
with the ulna and preventing inferior displacement of the radius. The lateral ulnar collateral ligament originates from the lateral epicondyle and blends with the fibers of the annular ligament proximally. It extends posteriorly to cradle the head–neck junction of the radius as it moves to its distal attachment at the supinator crest of the ulna (Fig. 10). This structure is one of the primary stabilizers of the elbow and is taut in flexion and extension. The accessory lateral collateral ligament is not uniformly present but represents discrete fibers that extend from the annular ligament to the supinator crest. When present, it may serve to stabilize the annular ligament during varus stress. Varus instability Lateral elbow instability related to isolated abnormalities of the lateral collateral ligament complex is not as well described as that on the medial side of the elbow. If it were to occur, the
mechanism would be a stress or force applied to the medial side of the articulation, resulting in compression on that side, with opening of the lateral articulation and subsequent insufficiency of the radial collateral ligament (Figs. 11, 12). As the radial collateral ligament attaches on and is intimately associated with the annular ligament, an abnormality discovered in one of the structures requires careful inspection of the other. Varus stress applied to the elbow may occur as an acute injury, but rarely as a repetitive stress as encountered on the medial side. Though lateral collateral ligament injuries rarely occur as the result of an isolated varus stress, other causes can commonly result in this injury, including dislocation, subluxation and overly aggressive surgery (release of the common extensor tendon or radial head resection). Varus instability is also tested with the elbow in full extension and 30 degrees of flexion to unlock the olecranon. A varus stress is applied to the elbow while palpating the lateral joint line. Posterolateral rotary instability and elbow dislocation The subject of elbow instability is complex and has been a challenge because of the difficulty establishing a mechanism of injury and reliable clinical tests for diagnosis. With the realization that elbow instability is more common than previously thought, marked advances in the understanding of this entity are occurring.
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Fig. 11. This diagram demonstrates the shearing and compressive forces associated with a varus stress at the elbow. The compression at the medial elbow results in opening of the lateral joint space, and potential insufficiency of the lateral supporting structures (capsule, radial collateral ligament complex, and common extensor tendon).
A simple classification for elbow instability does not exist. The literature points to five criteria that should be considered to produce a useful classification system for treatment: (1) timing (acute, chronic, recurrent), (2) articulation involved (elbow versus radial head), (3) direction of displacement (valgus, varus, anterior, posterolateral rotary), (4) degree of displacement (subluxation or dislocation), and (5) presence or absence of associated fractures [15]. For recurrent instability, posterolateral rotary instability is the most common pattern. This type of instability represents a spectrum of pathology consisting of three stages according to the degree of soft tissue disruption. In stage 1, there is posterolateral subluxation of the ulna on the humerus that results in insufficiency of the lateral ulnar collateral ligament (Fig. 13) [15–17]. In stage 2, the elbow dislocates incompletely so that the coronoid is
perched under the trochlea. In this stage, the radial collateral ligament, and anterior and posterior portions of the capsule, are disrupted in addition to the lateral ulnar collateral ligament. In stage 3, the elbow dislocates anteriorly so that the coronoid rests behind the humerus. Stage 3 is subclassified into three categories. In stage 3A, the anterior band of the medial collateral ligament is intact and the elbow is stable to valgus stress after reduction. In stage 3B, the anterior band of the medial collateral ligament is disrupted so that the elbow is unstable with valgus stress. In stage 3, the entire distal humerus is stripped of soft tissues, rendering the elbow grossly unstable even when a splint or cast is applied with the elbow in a semiflexed position. This classification system is helpful because each stage has specific clinical, radiographic, and pathologic features that are predictable and have implications for treatment [15]. Traditional teaching dictated that the mechanism of injury for elbow dislocation included hyperextension. More recently, it is believed that this mechanism is the result of a fall on the outstretched hand. The elbow experiences an axial compressive force during flexion as the body approaches the ground. As the body rotates internally on the elbow (forearm rotates externally on the humerus), a supination moment occurs at the elbow. This combination of valgus and supination with axial compression during flexion results in the posterolateral rotary subluxation or dislocation of the elbow. The corresponding pathoanatomy previously described can be thought of simply as the disruption of a soft tissue ring that progresses from posterolateral to medial in three stages [15]. Subluxation or dislocation of the elbow can be associated with fractures. Fracture dislocations most commonly involve the coronoid and radial head, a constellation of findings referred to as the ‘‘terrible triad’’ of the elbow because the injury complex is difficult to treat and prone to unsatisfactory results [15]. Radial head fractures do not cause clinically significant instability unless the medial collateral ligament is disrupted. An important feature of elbow injuries to recognize is that the small flake fracture of the coronoid, commonly seen in elbow dislocations, is not an avulsion fracture. Nothing attaches to the tip of the coronoid, rather the capsule attaches on the downward slope of the coronoid, the brachialis even more distal. This fracture is a shear fracture and is likely pathognomonic of an episode of elbow subluxation or dislocation (Fig. 14).
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Fig. 12. (A) Coronal T1-weighted MR image of the elbow in a 47-year-old man shows discontinuity of the radial collateral ligament (arrow) at the humeral attachment. The ligament also demonstrates somewhat abnormal morphology with thickening. The overlying common extensor tendon is normal. (B) Corresponding axial fat-suppressed proton density weighted MR image shows abnormal morphology and signal intensity (arrow) of the posterior attachment of the annular ligament, consistent with a high-grade partial tear.
A second consideration with respect to elbow dislocation is that as the ring of soft tissues is disrupted from posterolateral to medial, the capsule is torn and insufficient. In the absence of an intact capsule, joint fluid dissects through the soft tissue planes of the forearm, negating an indirect radiographic sign of trauma in the elbow, that of the joint effusion. Tendon anatomy and pathology The many muscles about the elbow can be divided into four groups: posterior, anterior, medial, and lateral. The muscles of the posterior group are the triceps and anconeus. The muscles of the anterior group are the biceps brachii and brachialis. The muscles in the medial group are the pronator teres, the palmaris longus, and the flexors of the hand and wrist. The muscles in the lateral group include the supinator, brachioradialis, and extensor muscles of the hand and wrist. Specific anatomic considerations and tendon
pathology commonly encountered in the elbow will be addressed. The classification of tendon injuries about the elbow can be organized by location, acuity, and degree of injury. Tendon injury related to a single isolated event is uncommon, although exceptions to this rule do occur. More commonly, tendinous injuries in this location relate to chronic repetitive microtrauma. MR imaging, with its excellent soft tissue contrast, is particularly well suited to diagnose tendon pathology. This is done primarily by close inspection of signal intensity and morphology of the tendons. As elsewhere in the body, the tendons about the elbow should be smooth, linear structures of low signal intensity. Abnormal morphology (attenuation or thickening) can be seen in tendinosis or tear. If signal intensity becomes bright or increased on fluid sensitive sequences within the substance of a tendon, a tear is present. Tears can be further characterized as partial or complete. A complete tear is diagnosed by a focal area of discontinuity.
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Fig. 13. Inversion recovery coronal MR image of the elbow in a 52-year-old man shows abnormal high signal intensity (arrows) in the expected position of the lateral ulnar collateral ligament, with no visualization of a normal ligament.
Common flexor tendon and medial muscles The muscular anatomy about the medial elbow is complex and includes three separate layers. The most superficial layer includes the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. The middle layer is comprised of the flexor digitorum superficialis, and the deep layer is made up of the flexor digitorum profundus. Only the flexor digitorum profundus does not take a part of its origin from the common flexor tendon. In rare cases, it may be necessary to localize pathology to a specific muscle group; however, the majority of pathology will occur in the common flexor tendon near its distal humeral attachment. Common extensor tendon and lateral muscles The lateral extensor muscles include the extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles. Only
Fig. 14. Sagittal fat-suppressed proton density weighted MR image demonstrates several findings of acute dislocation: (1) anterior subluxation of the humerus, (2) coronoid process fracture (arrow), (3) irregularity of the articular surface of the olecranon (curved arrow), and (4) disruption of the anterior and posterior capsule (double arrow). The corresponding coronal image (not shown here) further demonstrated complete disruption of the radial and ulnar collateral ligament complexes.
the extensor carpi radialis longus does not take a part of its origin from the common extensor tendon. As with the medial muscles, the vast majority of pathology encountered in this region is associated with the common extensor tendon rather than specific muscles. Epicondylitis and overuse syndromes Chronic stress applied to the elbow is the most frequent injury in athletes, and a spectrum of pathology can exist with varying degrees of severity. The frequency of involvement of the common flexor and extensor tendons to the medial and lateral epicondyles, respectively, has led to the designation of ‘‘epicondylitis’’ as a general term applied to these overuse syndromes. Anatomically, these overuse syndromes are classified by location and are further associated with sports that incite
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the pathology. The injury is believed to result from extrinsic tensile overload of the tendon, which, over time, produces microscopic tears that do not heal appropriately. Although these overuse entities about the elbow have been termed ‘‘epicondylitis’’ for the purpose of clinical diagnosis, inflammatory osseous changes rarely occur. The imaging findings are those reflecting chronic change in the tendon as evidenced by tendinosis alone or in conjunction with partial or complete tear. The distinction between types of pathology is made by consideration of morphology and signal intensity changes. Medial epicondylitis involves pathology of the common flexor tendon and is associated primarily with the sport of golfing. It also has been reported with javelin throwers, racquetball and squash players, swimmers, and bowlers. The pronator teres and flexor carpi radialis tendons are involved most frequently resulting in pain and tenderness to palpation over the anterior aspect of the medial epicondyle of the humerus and origin of the common flexor tendon. The mechanism of injury
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includes repetitive valgus strain with pain resulting from resisting pronation of the forearm or flexion of the wrist [18]. The imaging findings encountered can include tendinosis or tendinosis with superimposed partial or full thickness tear (Fig. 15). When assessing the tendon, it is necessary to closely scrutinize the underlying ulnar collateral ligament complex to ensure integrity. Lateral epicondylitis is the most common problem in the elbow in athletes and has been termed ‘‘tennis elbow.’’ This term may be somewhat inappropriate as 95% of cases of the clinical entity of lateral epicondylitis occur in non–tennis players [18]. Moreover, it has been estimated that 50% of people partaking in any sport with overhead arm motion will develop this process [19]. Lateral epicondylitis is associated with repetitive and excessive use of the wrist extensors. The pathology most commonly affects the extensor carpi radialis brevis at the common extensor tendon (Fig. 16). A number of investigators have described the pathology encountered in the
Fig. 15. (A) Frontal view of the elbow shows subtle irregularity (arrow) of the medial aspect of the distal humerus. (B) Coronal fat-suppressed T2-weighted fast spin echo image shows a focal full-thickness tear (arrow) of the attachment of the common flexor tendon to the medial epicondyle.
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Biceps tendon The biceps brachii muscle consists of two heads, the short head and long head. The short head arises from the tip of the coracoid process, in common with the coracobrachialis. The long head arises from the supraglenoid tubercle of the scapula. The two muscles join to form a common tendon 6 to 7 cm above the elbow joint line. This common tendon traverses the antecubital fossa to dive to its attachment at the radial tuberosity. An aponeurosis, the bicipital aponeurosis or lacertus fibrosus, arises from the musculotendinous junction, passes across the brachial artery, and merges with the fascia that covers the pronator teres and superficial flexors of the forearm. The distal biceps tendon does not have a tendon sheath, rather there is a bursa (cubital bursa) intimately associated with its attachment to the radial tuberosity [24]. Distal biceps tendon rupture
Fig. 16. Coronal fat-suppressed T2-weighted fast spin echo image of the elbow in a 50-year-old tennis player demonstrates abnormal morphology of the common extensor tendon with superimposed intrasubstance high signal intensity (arrow) consistent with a partial tear of the tendon. These imaging findings support the clinical diagnosis of tennis elbow.
degenerated tendon of this disease process. Histologically, necrosis, round cell infiltration, focal calcification, and scar formation have been shown [20]. In addition, invasion of blood vessels, fibroblastic proliferation, and lymphatic infiltration, the combination of which are referred to as angiofibroblastic hyperplasia, occur and ultimately lead to mucoid degeneration as the process continues [21,22]. The absence of a significant inflammatory response has been emphasized repeatedly and may explain the inadequacy of the healing process. The imaging findings in this process are exactly those encountered in the clinical entity of medial epicondylitis. As on the medial side, when pathology is encountered in the tendon, close scrutiny of the underlying ligamentous complex is necessary to exclude concomitant injury. In particular, thickening and tears of the lateral ulnar collateral ligament have been encountered with lateral epicondylitis [23].
Rupture of the tendon of the biceps brachii muscle at the elbow is rare, and constitutes less than 5% of all biceps tendon injuries [25]. It usually occurs in the dominant arm of males. Injuries to the musculotendinous junction have been reported, but the most common injury is complete avulsion of the tendon from the radial tuberosity. Although the injury often occurs acutely after a single traumatic event, the failure is thought to be the result of preexisting changes in the distal biceps tendon caused by intrinsic tendon degeneration, enthesopathy at the radial tuberosity, or cubital bursal changes. The typical mechanism of injury relates to forceful hyperextension applied to a flexed and supinated forearm. Athletes involved in strength sports, such as competitive weightlifting, football, and rugby, often sustain this injury. Clinically the patient gives a history of feeling a ‘‘pop’’ or sudden sharp pain in the antecubital fossa. The classic presentation of a complete distal biceps rupture is that of a mass in the antecubital fossa caused by proximal migration of the biceps muscle belly. Accurate diagnosis is more difficult in cases of the rare partial tear of the tendon, or more common complete tear of the tendon without retraction. The latter case can occur with an intact bicipital aponeurosis, which serves to tether the ruptured tendon to the pronator flexor muscle group (Fig. 17). MR imaging diagnosis of biceps tendon pathology becomes important in patients who do not present with the classic history or mass in the antecubital fossa, or for evaluation of the integrity
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Fig. 17. (A) Axial T1-weighted MR image shows abnormal morphology of the distal biceps tendon (arrow). The thickened lacertus fibrosus is intact (curved arrow). (B) Oblique coronal fat-suppressed T2-weighted MR image demonstrates a small stump of residual tendon (arrow) coursing toward the radial tuberosity. The high signal intensity around the tendon remnant is fluid within the cubital bursa.
of the lacertus fibrosus. MR imaging diagnosis of tendon pathology, as previously mentioned, is largely dependent on morphology, signal intensity, and the identification of areas of tendon discontinuity. In the case of the biceps tendon, an important indirect sign of tendon pathology is the presence of cubital bursitis (Fig. 17). With delayed diagnosis, chronic pain can ensue, as well as weakness in flexion, supination, and with grip strength. Treatment options favor surgical reattachment because nonoperatively treated ruptures have been reported to result in loss of 20% of elbow flexion strength and 40% of supination strength. If operative treatment is chosen, early repair is desirable, particularly when the lacertus fibrosus is ruptured and there is muscle retraction. If the lacertus fibrosus is intact, delayed primary repair is feasible [25]. Triceps tendon The triceps consists of three muscle bellies: the long head, the lateral head, and the medial head. The long head of the triceps arises by a strong
tendon from the infraglenoid tubercle of the scapula near the inferior margin of the glenoid cavity. It descends into the arm between the teres major and teres minor muscles. The lateral head originates from the posterior and lateral surfaces of the humerus and from the lateral intermuscular septum. The medial head arises from the posterior surface of the humerus, medial and below the radial groove, and from the medial and lower part of the lateral intermuscular septum. The tendon of the triceps descends to attach to the upper surface of the olecranon process of the ulna and to the antebrachial fascia near the laterally located anconeus muscle and tendon. Rupture of the triceps tendon is rare. The mechanism of injury has been reported to result from a direct blow to the triceps insertion or a deceleration force applied to the extended arm with contraction of the triceps as in a fall. Similar to pathology encountered in the distal biceps tendon, most ruptures occur at the insertion site, although musculotendinous junction and muscle belly injuries have been reported. Complete
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ruptures are more common than partial tears. Associated findings may include olecranon bursitis, subluxation of the ulnar nerve, or fracture of the radial head. Accurate clinical diagnosis relies on the presence of local pain, swelling, ecchymosis, a palpable defect, and partial or complete loss of the ability to extend the elbow. With more than 2 cm of retraction between the origin and the insertion, a 40% loss of extension strength can result [25]. For MR imaging diagnosis of triceps tendon pathology, it is imperative to be aware that the triceps tendon appearance is largely dependent on arm position. The tendon will appear lax and redundant when imaged in full extension, whereas it is taut in flexion. MR imaging features of a tear are similar to those associated with any other tendon. The treatment of a complete rupture is surgical repair; partial tears are often treated conservatively.
Summary There is a wide spectrum of pathology that affects the elbow in the athlete. This is further complicated by the complex anatomy of this articulation and the numerous normal anatomic variations that can serve as pitfalls in imaging diagnosis. A detailed knowledge of the anatomy and pathology that commonly affect this articulation can facilitate the ease and accuracy of imaging diagnosis. References [1] Rosenberg ZS, Beltran J, Cheung YY. Pseudodefect of the capitellum: potential MR imaging pitfall. Radiology 1994;191(3):821–3. [2] Rosenberg ZS, Beltran J, Cheung Y, Broker M. MR imaging of the elbow: normal variant and potential diagnostic pitfalls of the trochlear groove and cubital tunnel. AJR Am J Roentgenol 1995; 164(2):415–8. [3] Pincivero DM, Heinrichs K, Perrin DH. Medial elbow stability. Clinical implications. Sports Med 1994;18(2):141–8. [4] Bradley JP, Petrie RS. Osteochondritis dissecans of the humeral capitellum. Diagnosis and treatment. Clin Sports Med 2001;20(3):565–90. [5] Patel N, Weiner SD. Osteochondritis dissecans involving the trochlea: report of two patients (three elbows) and review of the literature. J Pediatr Orthop 2002;22(1):48–51.
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