DOI: 10.1148/rg.264055117
RadioGraphics 2006;26:1007-1020
© RSNA, 2006
US Diagnosis of UCL Tears of the Thumb and Stener Lesions: Technique, Pattern-based Approach, and Differential Diagnosis1
Farhad S. Ebrahim, MD,
Michel De Maeseneer, MD, PhD,
Tjeerd Jager, MD,
Stefaan Marcelis, MD,
David A. Jamadar, MB, BS, FRCS, DMRD and
Jon A. Jacobson, MD
1 From the Department of Radiology, University of Michigan Health System, Taubman/B-1/Room 132, Box 0302, 1500 E Medical Center Dr, Ann Arbor, MI 48109-0302 (F.S.E., M.D.M., D.A.J., J.A.J.); the Department of Radiology, Aalsters Stedelijk Ziekenhuis, Aalst, Belgium (T.J.); and the Department of Radiology, University of Lie`ge, Lie`ge, Belgium (S.M.). Recipient of a Certificate of Merit award for an education exhibit at the 2004 RSNA Annual Meeting. Received May 12, 2005; revision requested June 13 and received September 15; accepted September 16. All authors have no financial relationships to disclose.
Address correspondence to F.S.E. (e-mail: febrahim{at}umich.edu).
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Abstract
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The thumb is a central component supporting the intricate movements of the hand.
Patients with acute thumb pain, particularly after trauma, require prompt evaluation of structural integrity, thus avoiding long-term morbidity such as instability, chronic pain, and osteoarthritis.
Injury to the ulnar collateral ligament (UCL) of the thumb requires imaging for diagnosis of surgically important entities such as the Stener lesion. Historically, routine radiography including stress views does not allow such diagnosis and is potentially detrimental to patient care. Both magnetic resonance imaging and ultrasonography (US) are currently used for direct evaluation of the UCL of the thumb and are safe and accurate. US is more dynamic and less time-consuming and may be easier to perform. Furthermore, other disorders such as tenosynovitis, tendon tears, and articular pathologic conditions can involve the thumb and thenar region and may also be diagnosed with US. In this context, US is an underused tool because it is potentially an adjunct to the clinical examination in the appropriate setting. A sound knowledge of the regional anatomy and basic training in the principles of US should equip the imager with the skills necessary to evaluate the UCL of the thumb and its surrounding structures.
© RSNA, 2006
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:- Describe the basic techniques used to perform US of the UCL of the thumb.
- Identify the US features of UCL injury of the thumb with emphasis on the Stener lesion.
- List the US features of other common acute conditions affecting the base of the thumb.
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Introduction
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The thumb is a central component supporting the intricate movements of the hand. Stability and motion are dependent on a delicate system of fibrous articulating elements, tendons, and collateral ligaments including the ulnar collateral ligament (UCL) of the metacarpophalangeal joint. In an acute setting, prompt evaluation of structural integrity after trauma is the key to avoiding long-term morbidity. UCL tears are also referred to as gamekeeper’s thumb or skier’s thumb (1).
Campbell and colleagues described the occupational hazard of ligamentous insufficiency of the UCL of the thumb in Scottish gamekeepers in 1955 (2). The method of killing a wounded rabbit placed stress on the ulnar aspect of the thumb and subsequently led to injury of the ligament. Currently, acute and chronic injury of the UCL is often related to skiing injuries, more specifically those caused by the ski pole.
The mechanism of injury in the development of gamekeeper’s thumb has been well reviewed in the literature (2–4). Damage to the UCL is caused by hyperabduction of the metacarpophalangeal joint accompanied by varying degrees of hyperextension. Associated compromise of neighboring structures may produce loss of pinch and grasp strength. Ultimately, the injury may culminate in chronic pain and osteoarthritis.
The UCL together with the base of the first proximal phalanx form a bone-ligament complex that resists valgus stress at the metacarpophalangeal joint (3). Theoretically, integrity should be simple to confirm clinically. However, pain, swelling, and concern about exacerbation of the injury can hamper physical examination. This creates two pitfalls: the first is incorrect classification of a UCL injury, and the second is a wrong diagnosis.
Routine radiographs have always been the foundation of imaging algorithms. Therefore, the absence of any obvious fractures on standard radiographs has created a tendency for physicians to request "stress radiographs" of the thumb in the setting of "possible ulnar metacarpophalangeal injury" (Fig 1). Results of such radiographs are often difficult to interpret. Furthermore, there is concern that stress tests may transform nonsurgical injuries into surgical injuries.
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Figure 1. Results of stress testing in a 35-year-old man. Radiographs of the metacarpophalangeal joints of the thumbs show asymmetric widening (arrows), which is greater on the left side (the normal joint) than on the right (the injured joint).
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Both magnetic resonance (MR) imaging and ultrasonography (US) allow direct visualization of the entire UCL bone-ligament complex and its accompanying structures, thereby providing the vital clinical information to the surgeon (2,4,5). Categorization of the tears into surgical and nonsurgical abnormalities is crucial and cannot always be accomplished with radiography.
The Stener lesion and displaced full-thickness tears are usually treated surgically (6). A Stener lesion occurs when the adductor aponeurosis becomes interposed between the ruptured UCL and its site of insertion at the base of the proximal phalanx.
Our aim was to evaluate the utility of US in the acute setting. US was performed by three experienced radiologists in 32 patients with a clinical suspicion of UCL injury. Patients at three institutions were included in the study. The final diagnosis was based on results of surgery or combined clinical-US follow-up. Two embalmed cadaveric specimens were dissected and one fresh specimen was sectioned, and the results were correlated with imaging findings. US images were interpreted by means of consensus between two musculoskeletal radiologists experienced in limb US.
US is more dynamic and less time-consuming and may be easier to perform in an emergency setting. Furthermore, other disorders such as tenosynovitis, tendon tears, and articular pathologic conditions can involve the thumb and thenar region and may also be diagnosed with US (7,8). Follow-up examinations are also more practical with US. Although MR imaging is a useful alternative, US remains an underused tool since it is potentially an adjunct to the clinical examination in this context.
In this article, we outline a simple method of performing US of the thumb and discuss the spectrum of common acute disorders encountered with particular emphasis on UCL injuries.
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Anatomic Background
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Clinically relevant anatomy about the first metacarpophalangeal joint includes the following: the radial and ulnar collateral ligaments, the volar plate, the extensor tendons and their dorsal reinforcements, the flexor tendon and sheaths including pulley systems, as well as the thenar muscles including the adductor pollicis muscle and its aponeurosis.
The metacarpophalangeal joint is a condylar articulation reinforced by ulnar and radial collateral ligaments (Figs 2, 3). The UCL originates from the metacarpal head, coursing from proximal and dorsal to distal and palmar in direction, where it inserts on the medial tubercle of the proximal phalanx. It is 4–8 mm in width and 12–14 mm in length. Some ligament fibers extend to the volar plate, which is a fibrous supporting structure (Fig 4). Other fibers contribute to the dorsal reinforcements that keep the extensor pollicis longus tendon centered at the metacarpal head (9). The extensor pollicis brevis tendon usually terminates at the dorsal aspect of the first metacarpophalangeal joint, although it may accompany the extensor pollicis longus to insert on the base of the distal phalanx (Fig 5).
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Figure 2. Axial anatomic section of the first metacarpophalangeal joint shows the extensor tendons (ET), flexor tendons (F), radial collateral ligament (R), and UCL (U). A white aponeurosis (black arrows) covers the UCL. White arrow = adductor pollicis.
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Figure 3. Axial drawing of the first metacarpophalangeal joint shows the radial collateral ligament (R), extensor tendons (T), and UCL (U). Note the normal superficial relationship of the adductor aponeurosis (arrows) to the UCL.
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Figure 5. Photograph of the dorsal first-to-second web space shows the first dorsal interosseous muscle (DI). The extensor pollicis brevis (EPB) is located more radially than the extensor pollicis longus (EPL). The adductor pollicis is intimately attached to the ulnar side of the first metacarpophalangeal joint (arrow).
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The thenar region comprises four muscles operating the carpometacarpal joint of the thumb. They are the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and adductor pollicis. They attach volar to the ulnar and radial sesamoids of the thumb, with the flexor pollicis longus passing between the sesamoids to insert on the base of the distal phalanx (Fig 6). It is important to appreciate that the aponeurosis of the adductor pollicis (thenar) covers the UCL of the thumb superficially. The flexor tendon is enveloped by a tendon sheath that usually extends from the wrist area (Fig 7).
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Figure 7. An-teroposterior radiograph of a cadaveric hand shows the synovial sheath of the flexor pollicis longus (arrows), which was injected with iodinated contrast material. The synovial sheath extends from the wrist toward the tip of the thumb.
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Examination Technique
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The hand is placed flat on the table. A 12–13-MHz linear probe is used. US gel may be used liberally to optimize near-field imaging, avoiding the need for a standoff pad. The US probe is then slid from the second finger onto the first metacarpophalangeal joint to obtain either a transverse or longitudinal image of the UCL (Fig 8). US examination of the UCL typically takes less than 1 minute. Other injuries may mimic UCL tear, or injuries such as volar plate lesions may be associated with UCL tear. Valgus and varus stress tests are not encouraged at our institution due to concern over aggravating an injury. However, these tests still remain theoretically possible with US. Additional attention is focused on evaluation of the thenar region and the dorsal, palmar, and radial aspects of the thumb. Dynamic maneuvers such as clenching the fist are helpful in assessing tendon stability. Doppler imaging can also be an adjunct for evaluating synovium or vascular structures. The contralateral side can always serve as a control.
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Figure 8. Photograph of the dorsal aspect of the first web space in a 38-year-old volunteer shows the technique for scanning the UCL. A high-frequency US probe can be directed from the second digit (2) onto the ulnar side of the thumb in the longitudinal plane (L). In addition, a transverse section (T) can be obtained at the first metacarpophalangeal joint. 3 = third digit.
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The normal UCL is a hyperechoic structure spanning the ulnar side of the first metacarpophalangeal joint. Its configuration predisposes the deep fibers to anisotropy (Figs 9, 10). Superficially, it is covered by an additional thin hyper-echoic band corresponding to the adductor pollicis aponeurosis, which is variably visualized in the normal situation, depending on the employed US equipment.
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Figure 10. Coronal US scan of the thumb of a 30-year-old volunteer shows a normal UCL (arrows). The deeper fibers of the UCL appear anisotropic. MCP = metacarpal, PP = proximal phalanx.
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Patterns and Clinical Relevance of UCL Injury
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The spectrum of UCL injury (Fig 11) includes strain (Fig 12), partial-thickness tear (Fig 13), and full-thickness tear (Fig 14) (10,11). Associated findings may include bone avulsion, joint effusion, volar plate injury, and Stener lesion (Figs 15,16).
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Figure 13. Partial-thickness UCL tear. Coronal US scan of the thumb shows thickening (T) of the proximal UCL. There is a hypoechoic incomplete tear (thin arrow) in the ligament with intact overlying superficial fibers (SF). MCP = metacarpal, PP = proximal phalanx, thick arrow = aponeurosis.
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Figure 14. Full-thickness UCL tear. Coronal US scan of the thumb shows a hypoechoic cleft (white arrow) that extends through the UCL. The proximal ligament (cursor) is still covered by the smooth aponeurosis (black arrows). MCP = metacarpal, PP = proximal phalanx.
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Figure 15. Stener lesion in a 28-year-old man. Coronal US scan of the thumb shows a proximally retracted nodule with an irregular lobulated outline (arrows), an appearance diagnostic of a Stener lesion. The nodule represents the retracted proximal segment of the UCL and is consistent with a full-thickness tear. Displacement of this segment superficial to the aponeurosis results in loss of the smooth contour of the aponeurosis and surface lobulation. MCP = metacarpal, PP = proximal phalanx.
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Figure 16a. Stener lesion. (a) Coronal US scan of the thumb shows a proximal lobulated nodule (S, arrows), which represents the retracted displaced proximal segment of the UCL. The smooth contour of the aponeurosis is distorted by the superficially lying ligament, resulting in bulging of the surface of the aponeurosis. MCP = metacarpal, PP = proximal phalanx. (b) Axial US scan of the thumb shows a thickened lobulated UCL (cursors). There is loss of the smooth contour of the aponeurosis with bulging (arrow). The diagnosis can be made by using the same criteria as on coronal scans. The left side of the image is radial. ET = extensor tendon, MCP = metacarpal head, TH = thenar eminence. (c) Axial US scan of the thumb, obtained for comparison with b, shows a normal UCL. The adductor aponeurosis (black arrowheads) covers the muscle and UCL (white arrowhead). Note the anisotropy of these structures. There is no nodule, lobulation, or bulging. The right side of the image is radial. ET = extensor tendon, MCP = metacarpal head, TH = thenar eminence.
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Figure 16b. Stener lesion. (a) Coronal US scan of the thumb shows a proximal lobulated nodule (S, arrows), which represents the retracted displaced proximal segment of the UCL. The smooth contour of the aponeurosis is distorted by the superficially lying ligament, resulting in bulging of the surface of the aponeurosis. MCP = metacarpal, PP = proximal phalanx. (b) Axial US scan of the thumb shows a thickened lobulated UCL (cursors). There is loss of the smooth contour of the aponeurosis with bulging (arrow). The diagnosis can be made by using the same criteria as on coronal scans. The left side of the image is radial. ET = extensor tendon, MCP = metacarpal head, TH = thenar eminence. (c) Axial US scan of the thumb, obtained for comparison with b, shows a normal UCL. The adductor aponeurosis (black arrowheads) covers the muscle and UCL (white arrowhead). Note the anisotropy of these structures. There is no nodule, lobulation, or bulging. The right side of the image is radial. ET = extensor tendon, MCP = metacarpal head, TH = thenar eminence.
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Figure 16c. Stener lesion. (a) Coronal US scan of the thumb shows a proximal lobulated nodule (S, arrows), which represents the retracted displaced proximal segment of the UCL. The smooth contour of the aponeurosis is distorted by the superficially lying ligament, resulting in bulging of the surface of the aponeurosis. MCP = metacarpal, PP = proximal phalanx. (b) Axial US scan of the thumb shows a thickened lobulated UCL (cursors). There is loss of the smooth contour of the aponeurosis with bulging (arrow). The diagnosis can be made by using the same criteria as on coronal scans. The left side of the image is radial. ET = extensor tendon, MCP = metacarpal head, TH = thenar eminence. (c) Axial US scan of the thumb, obtained for comparison with b, shows a normal UCL. The adductor aponeurosis (black arrowheads) covers the muscle and UCL (white arrowhead). Note the anisotropy of these structures. There is no nodule, lobulation, or bulging. The right side of the image is radial. ET = extensor tendon, MCP = metacarpal head, TH = thenar eminence.
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UCL injuries are common, and the management dilemma is whether to treat them conservatively or surgically (1). Since the UCL is a capsular ligament, nondisplaced ligamentous rupture can often be treated conservatively. Partial-thickness tears and minimally displaced full-thickness tears are usually treated conservatively with favorable results (4). Thus, the degree of displacement is an important consideration.
In the presence of an avulsion fragment from the base of the proximal phalanx, this assessment may sometimes be made on routine radiographs. However, avulsion fragments are uncommonly seen on radiographs (12% of injuries) (4). Therefore, in most patients, plain radiographs cannot provide a landmark for evaluating ligament displacement. The most extreme example of this shortcoming is in cases of Stener lesion.
A normal UCL lies deep to the adductor aponeurosis. In Stener lesion, there is significant retraction of the proximal fragment, which then dislocates superficial to the aponeurosis. Therefore, the ruptured ends of the ligament are no longer in contact. This precludes successful primary healing, resulting in long-term morbidity.
Only cross-sectional imaging such as US or MR imaging allows direct visualization of these injured fibers. US features of Stener lesion parallel the findings described on MR images by Harper et al (2). The UCL tear is considered displaced when it is retracted, is folded on itself, and moves proximal to the adductor aponeurosis, creating the appearance of a "yo-yo on a string" on coronal scans. The retracted balled-up "yo-yo" is the torn displaced UCL, and the "string" is the associated adductor aponeurosis. Pitfalls in US diagnosis of Stener lesions are more frequent if there is more than a 1-week delay in imaging (1). In this situation, MR imaging has been advocated but may prove to be as challenging.
A further area where evaluation of the entire bone-ligament complex is appropriate is the uncommon two-level UCL injury. This lesion consists of both an undisplaced avulsion fragment and a displaced ligament tear (3). Although the osseous fragment can be seen on radiographs, this misleads the unsuspecting clinician into assuming an undisplaced UCL ligament. The patient is treated conservatively, with serious consequences. The only clue on radiographs will be a poorly visible, smaller bone fragment situated more proximally. However, if the thumb is imaged with US, a displaced UCL attached to this smaller fragment will be appreciated. The patient can therefore undergo primary repair with full functional recovery.
Owing to its low cost and easy accessibility, US has proven to be a valuable aid to the surgeon in the decision to operate. In the hands of specialist orthopedic hand surgeons, the positive predictive value for ruptures of the UCL is higher with US (94%) than clinical examination (80%) (4).
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Differential Diagnostic Considerations
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Other conditions may mimic UCL injury. These include dorsal hood tear, tendon tear, joint effusion, bone injury, and vascular injury.
Ulnar Side: Dorsal Hood Injury
Dorsal hood tear with ulnar displacement of the extensor pollicis longus tendon may occur. A normal dorsal hood is characteristically a regular hypoechoic band arising from the edges of the common extensor tendons. This in part may be related to anisotropy. Dorsal hood injuries of the thumb are less common than those involving the fingers. A direct blow is the most common mechanism, and generally the diagnosis is clinically evident. However, if there is considerable swelling, clinical examination results can be misleading.
Dynamic US can be helpful. The tendon maintains its position over the metacarpal in the neutral position (Fig 17a). Because the hood is responsible for sagittal stability, the injured tendon has a propensity to dislocate ulnar to the thumb when flexed (Fig 17b). The tendon generally relocates on extension. However, occasionally it is trapped in the anatomic snuffbox. We have witnessed this in a patient whose injury was misdiagnosed as a UCL lesion; it proved to be a dorsal hood injury at surgery. Hood injuries may also occur in a nontraumatic setting in patients with rheumatoid arthritis (12).
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Figure 17a. Dorsal hood injury of the thumb in a 16-year-old girl. The left side of the images is ulnar, and the right side is radial. (a) Axial US scan of the normal thumb, obtained for comparison, shows the extensor pollicis longus (L) and brevis (B) tendons centered over the metacarpal head. Arrow = cortical edge of metacarpal head. (b) Axial US scan of the injured thumb shows the extensor pollicis longus tendon (L) displaced over the cortical edge (arrow) of the metacarpal head.
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Figure 17b. Dorsal hood injury of the thumb in a 16-year-old girl. The left side of the images is ulnar, and the right side is radial. (a) Axial US scan of the normal thumb, obtained for comparison, shows the extensor pollicis longus (L) and brevis (B) tendons centered over the metacarpal head. Arrow = cortical edge of metacarpal head. (b) Axial US scan of the injured thumb shows the extensor pollicis longus tendon (L) displaced over the cortical edge (arrow) of the metacarpal head.
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Ulnar Side: Thenar Muscle Injury
Ulnar-sided lesions also include thenar injuries. Sonographic evaluation of each of the four thenar muscles has been described in the literature (13). Muscle injuries can arise from compression or distraction forces (14). The typical normal architecture of muscle as seen on longitudinal sections is generally evident; that is, there is a "herring-bone" pattern of hypoechoic skeletal muscle bundles separated by longitudinally aligned echo-genic connective tissue (epimysium). On the transverse section, the epimysium is seen end-on and therefore appears as an echogenic dot.
Muscle tears undergo evolution in echo pattern with the passage of time. This closely correlates with the associated pathologic stages. However, they generally appear as areas of decreased echogenicity (Fig 18). More extensive partial or complete ruptures of muscle may demonstrate retraction of frayed muscle ends and a resulting gap or hematoma. Dissecting hematomas between muscles produce areas of anechoic fluid that bulge into the nearby muscles but leave their internal architecture intact. Hemorrhage may also appear hyperechoic or isoechoic to muscle. Ultimately, scar and calcifications may develop.
Radial Side: Ligament Injury
The intrinsic anatomy of the radial side of the first metacarpophalangeal joint is not a mirror image of that of the ulnar aspect. This accounts for distinctive patterns of instability. Whereas a disrupted UCL in conjunction with dorsal capsular tears is apt to result in combined radiovolar sub-luxation, disruption of the radial collateral ligament, coupled with the unopposed dynamic force of the adductor pollicis, characteristically is prone to produce a rapid pathologic sequence of profound joint instability, with progressive ulnar and volar subluxation and ultimately degenerative joint disease (15). It has been shown that rotational and volar stability is also augmented by a contribution from the extensor pollicis brevis capsule attachment. Radial collateral ligament tears are less common in the thumb than in the fingers. The ligament can be elongated (Fig 19), ruptured, or associated with bone avulsion.
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Figure 19a. Strain of the radial collateral ligament. The left side of the images is distal. (a) Coronal US scan of the thumb shows a thickened elongated radial collateral ligament (R). (b) Coronal US scan of the contralateral thumb, obtained for comparison, shows a normal radial collateral ligament (arrows).
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Figure 19b. Strain of the radial collateral ligament. The left side of the images is distal. (a) Coronal US scan of the thumb shows a thickened elongated radial collateral ligament (R). (b) Coronal US scan of the contralateral thumb, obtained for comparison, shows a normal radial collateral ligament (arrows).
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The US characteristics of tears are similar to those of UCL tears with the exception of complications such as Stener lesion, which do not occur given anatomic differences. Some authors still selectively recommend surgical repair to restore stability against varus stress and volar subluxation (16,17).
Radial Side: de Quervain Disease
In normal states, the synovial sheath of extensor tendons is barely seen as a thin, well-defined, circumferential hypoechoic rim less than 1 mm thick. In tenosynovitis, the increased amount of synovial fluid typically appears as a hypoechoic collection surrounding the hyperechoic tendon (Fig 20). Thickening of the synovial sheath may be observed (18).
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Figure 20. de Quervain disease. Axial US scan of the base of the thumb shows both the abductor pollicis longus and extensor pollicis brevis tendons (arrow), which are situated within a distended synovial sheath with low levels of internal echoes (arrowheads). This appearance is consistent with tenosynovitis. (Courtesy of Cynthia Fan, MD, University of Michigan, Ann Arbor.)
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de Quervain disease is produced by repeated chronic microtrauma at the level of the extensor retinaculum of the wrist. This results in possible tendinosis of the extensor pollicis brevis and abductor pollicis longus tendons with thickening of the retinaculum. At US, there is swelling of the affected tendons, which may change to a more hypoechoic pattern with areas of heterogeneity. Fluid in the tendon sheath is more common in acute cases. Tendon changes are more likely in the chronic setting. A thickened and hypoechoic retinaculum, usually observed in chronic cases, suggests the need for surgical decompression. Hyperemia and adjacent bone changes may occur.
The presence of normal variants enhances the value of imaging, especially when guiding treatment. An example of this is the absence of the extensor pollicis brevis tendon in 6% of normal individuals. In this situation, the abductor pollicis tendon may be multilamellar, simulating longitudinal tears. More than a single abductor tendon may coexist separated by a septum in 40% of wrists. The lack of communication between these tendon sheaths may explain absent or incomplete response to a unicompartmental steroid injection (19).
Radial Side: Arthritic Disease of the Carpometacarpal Joint
Bone profile and cartilage are the primary landmarks in the assessment of joints. The bone pro-file is a sharp hyperechoic line. The normal cartilage is a subtle hypoechoic band. Joint cavity widening is the most characteristic feature of acute or chronic synovitis. Radiographs are limited in their ability to allow diagnosis of early disease and characterization of soft-tissue or synovial processes (20).
A wide range of cartilaginous manifestations can be detected in chronic arthritis by using US. These include loss of sharpness of the outer margin, loss of clarity of the cartilaginous layer, cartilage thinning, and subchondral bone profile irregularities. Any early erosions can also be sought, which may allow differentiation between erosive and degenerative disease. The effect of multiple osseous fragments can be determined in relation to surrounding structures. More specifically, in the setting of decreased range of movement or instability, one can differentiate between intraarticular loose bodies (Fig 21) and osseous spurs or heterotopic bone. Any impingement on tendons, ligaments, and blood vessels can be identified. An example of this is tenosynovitis around the flexor carpi radialis tendon in the setting of first carpometacarpal joint osteoarthrosis (19).
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Figure 21. Degenerative disease of the carpometa-carpal joint in a 60-year-old woman. Sagittal US scan of the carpometacarpal joint shows joint effusion (black arrows) and intraarticular bodies (white arrow). The left side of the image is distal.
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Synovial proliferation can be sought by evaluating the echogenicity, compressibility, and homogeneity of the synovial tissues. Active synovitis produces increased synovial perfusion, which is evident on power Doppler scans (20). The presence of periarticular lesions (eg, ganglion cysts) and the integrity of the surrounding supporting elements (ie, tendons and ligaments) can be con-firmed.
Radial Side: Vascular Injury
Because of their superficial location and proximity to the bone, vessels of the hand and wrist are predisposed to trauma (18). This explains the high frequency of traumatic diseases of the superficial branch of the radial artery where it courses over the tubercle of the trapezium. Repetitive microtraumas to the vessel wall may cause intimal thickening with fibrin deposits, thrombosis, and pseudoaneurysms.
US and color Doppler imaging demonstrate hypoechoic clot filling the vessel lumen, with a lack of pulsation or color flow. These findings are often propagated into the collateral pathways. This entity can be an unexpected finding during evaluation at the base of the thumb and first metacarpophalangeal joint (Fig 22).
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Figure 22a. Vascular injury in an active young woman with pain at the base of the thumb. (a) Coronal US scan of the base of the contralateral thumb, obtained for comparison, shows the superficial branch of the radial artery (RA), which has a normal appearance. (b) Coronal US scan of the base of the symptomatic thumb shows a faint echogenic line (T) parallel to the wall of the radial artery, an appearance consistent with intraluminal thrombosis.
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Figure 22b. Vascular injury in an active young woman with pain at the base of the thumb. (a) Coronal US scan of the base of the contralateral thumb, obtained for comparison, shows the superficial branch of the radial artery (RA), which has a normal appearance. (b) Coronal US scan of the base of the symptomatic thumb shows a faint echogenic line (T) parallel to the wall of the radial artery, an appearance consistent with intraluminal thrombosis.
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Dorsal Side: Pathologic Conditions of the Extensor Tendons
In the acute setting, an extensor pollicis longus tear may simulate other injuries around the thumb base. The diagnosis is usually clinically obvious as there is loss of extension. Confounding factors such as associated wrist fracture often render this test unreliable, hence the need for imaging. MR imaging is considered less reliable in evaluation of the extensor pollicis longus because of its susceptibility to the magic angle artifact. At the wrist level, the extensor pollicis longus crosses to the thumb at a 55° angle (21). In addition the extensor pollicis longus, in contradistinction to the adjacent tendons, is flat at its crossing point over the extensor carpi radialis brevis and longus tendons, and even in the normal setting it may be difficult to depict on MR images with dedicated surface coils. This may be corrected by repositioning; however, US can obviate these difficulties.
At US, partial-thickness tendon tears appear as tendon swelling, echotexture abnormalities (eg, a hypoechoic cleft), and signs of tendon discontinuity. Complete tears appear as retraction of the tendon stump. As these tears may occur proximally in the wrist or more distally at the distal phalangeal base, location and degree of displacement guide surgical management. The tendon stump may manifest clinically as a mass, prompting imaging. Dynamic examination will reveal absence of the normal sliding movement of the tendon during muscle contraction and relaxation. The retracted tendon stumps quite often are replaced by a tubular hypoechoic area adjacent to the carpal bones (Fig 23). This represents a synovial sheath distended by fluid, hemorrhage, and scar tissue (18,19).
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Figure 23. Proximal rupture of the extensor pollicis longus tendon. Sagittal US scan of the carpal region shows a fusiform hypoechoic synovial sheath (arrows). This finding is due to proximal retraction of a torn extensor pollicis longus tendon, leaving the sheath empty. The proximal tendon stump is not seen in the image but may manifest as a mass at clinical examination, thus prompting imaging.
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The extensor pollicis longus tendon may be avulsed from the distal phalanx, a situation similar to mallet finger (21) (Fig 24). This is caused by acute forceful flexion of the extended distal interphalangeal joint. The injury may be associated with a fracture of the dorsal base of the distal phalanx.
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Figure 24. Distal rupture of the extensor pollicis longus tendon (mallet finger). Sagittal US scan shows a cleft (arrow) in the extensor pollicis longus tendon. Note that the distal interphalangeal joint is held in slight flexion. DP = distal phalanx, PP = proximal phalanx. (Courtesy of Freddy Machiels, MD, Free University, Brussels, Belgium.)
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Abnormalities of the extensor tendons commonly occur in the setting of inflammatory conditions such as rheumatoid arthritis or psoriasis (Fig 25). The tendon may be invaded by the adjacent pannus with resultant rupture (19). Tendinosis may also occur from the mechanical effects of posttraumatic osseous change (Fig 26).
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Figure 25. Synovitis in a patient with psoriasis. Sagittal US scan of the dorsal metacarpophalangeal joint of the thumb shows that the extensor tendon (short arrows) is displaced by synovial hypertrophy and effusion (long arrows). The tendon demonstrates mild anisotropy due to mass effect from the joint inflammation. The left side of the image is distal.
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Figure 26. Extensor tendinosis in a 34-year-old woman. Sagittal US scan of the dorsal metacarpophalangeal joint shows a thickened extensor pollicis brevis tendon (ET). Posttraumatic development of an osseous excrescence (arrow) resulted in chronic repetitive friction against the adjacent tendon, culminating in tendinosis. MCP = metacarpal.
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Palmar Side: Volar Plate Injury
The volar plate is a thick fibrocartilaginous structure that constitutes the palmar aspect of the metacarpophalangeal joint capsule. It is also present at the proximal interphalangeal joint. It prevents hyperextension of the joint and is an intimate component of the surrounding capsular reinforcements. At US, it appears as a triangular echogenic structure (Figs 27a, 28) deep to the flexor pollicis longus tendon. In the neutral position, this relationship may result in normal "displacement" of the flexor tendon in relation to the bony surface landmarks (Fig 27a). During flexion, the plate normally "accordions" and appears less masslike.
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Figure 27a. Normal and abnormal volar plate. MCP = metacarpal. (a) Sagittal US scan of the ventral metacarpophalangeal joint in the neutral position shows a normal volar plate (cursors). Note the normal displacement of the flexor pollicis longus tendon (arrowheads) from the osseous landmarks. The left side of the image is proximal. (b) Sagittal US scan of the ventral metacarpophalangeal joint of the thumb shows a hypoechoic swollen volar plate (black arrows) with a central cleft (white arrows). The cleft represents a tear through the substance of the volar plate. The apparent malalignment of the proximal phalanx (PP) is an artifact created by the scanning plane.
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Figure 27b. Normal and abnormal volar plate. MCP = metacarpal. (a) Sagittal US scan of the ventral metacarpophalangeal joint in the neutral position shows a normal volar plate (cursors). Note the normal displacement of the flexor pollicis longus tendon (arrowheads) from the osseous landmarks. The left side of the image is proximal. (b) Sagittal US scan of the ventral metacarpophalangeal joint of the thumb shows a hypoechoic swollen volar plate (black arrows) with a central cleft (white arrows). The cleft represents a tear through the substance of the volar plate. The apparent malalignment of the proximal phalanx (PP) is an artifact created by the scanning plane.
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Figure 28. Infectious tenosynovitis. Sagittal US scan of the flexor pollicis tendon (T) shows hypoechoic synovial reaction (white arrows) adjacent to the tendon. Incidentally noted is a normal volar plate (black arrow).
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Volar plate injuries are a result of forced hyperextension of the metacarpophalangeal joint or rotational longitudinal compression in the fingers. In the thumb, volar plate lesions are more common in the setting of UCL injury and therefore should be routinely assessed (Fig 27b). Associated osseous avulsions reflect a more advanced stage in the spectrum of injury, which includes isolated plate injuries that are radiographically silent. Although dislocation of the metacarpophalangeal joint is uncommon, a complex dislocation may resist reduction on account of volar plate interposition. This will require open reduction.
MR imaging of the fingers has been employed in both of these conditions to evaluate the state of the volar plate and to precisely identify its location and displacement (22). Given its small field of view and dynamic capabilities, US has the potential to rival MR imaging in this application, although this will require further study.
Palmar Side: Pathologic Conditions of the Flexor Tendons
US can be useful in the diagnosis of flexor tendon tenosynovitis (Fig 28). In acute tenosynovitis, fluid is present within the synovial sheath. The echogenicity of the fluid varies according to its composition and the cause of the disease (19,23). Rheumatoid arthritis is the most common inflammatory cause of tenosynovitis. Rupture of the flexor pollicis longus tendon may occur as a consequence of synovial pannus invasion. In subacute and chronic cases, thickening of the tendon, synovial sheath, or both may be observed. The amount of fluid is variable. Sometimes it is challenging to distinguish fluid from synovial thickening, and various factors have been cited as being helpful. These include differences in echogenicity, displacement of echoes on active movement, compressibility of the joint capsule, and flow at Doppler imaging (20).
The flexor carpi radialis tendon is another structure that may be associated with pain and loss of mobility around the base of the thumb. This tendon occupies a narrow fibro-osseous tunnel at the level of the crest of the trapezium. Tendinosis may be secondary to osteoarthrosis of the first carpometacarpal joint or of the trapezioscaphoid joint and scaphoid fractures. This may culminate in tendon rupture, so surgical release may be required (19).
Calcific tendinitis of the wrist and hands is uncommon but has been described in flexor tendons (24). Associated trauma can be a confounding factor in the diagnosis. It manifests as an acute inflammatory reaction and soft-tissue calcifications, which may be seen at US. US can also be used to guide dissolution of the calcium and injection of a local anesthetic or steroid in the acute clinical setting.
Palmar Side: Trigger Thumb
Trigger finger is primarily characterized by transient locking of the flexed finger, which is followed by painful snapping during extension. Occasionally, the finger may be trapped in extension. It is usually idiopathic and occurs commonly in middle-aged women. It develops more frequently in diabetic patients and patients with osteoarthritis. At the center of the proposed pathophysiology is the digital annular pulley system, which is primarily responsible for prevention of tendon "bowstringing" during flexion. Although the effect of pulley lesions has been studied in the second to fifth digits, the literature is fairly sparse concerning the first digit. This may relate to the low incidence of thumb pulley injuries.
The flexor anatomy of the thumb differs from that of the fingers. The single flexor pollicis longus tendon sheath has two annular pulleys (A1 at the metacarpophalangeal joint and A2 at the proximal interphalangeal joint). As a consequence, the effect of pulley injuries on tendon bowstringing in the thumb cannot automatically be extrapolated from effects seen in the other digits. Repetitive movements lead to thickening of the annular pulleys and swelling of the flexor tendon, which ultimately may develop a nodule that causes entrapment. The A1 pulley is the most commonly involved. Surgical release of this pulley is a key component of clinical management.
Although the diagnosis of trigger finger is clinical, US can be a valuable adjunct. It allows evaluation of the integrity of the tendon. Diffuse tenosynovitis can be differentiated from a localized pulley lesion. The pulley is normally a thin hypo-echoic band (Fig 29a). Thickening (Fig 29b) and partial or complete disruptions of the pulleys can be directly visualized. Diagnosis of focal tendon thickening (Fig 30) or ganglion formation can aid preoperative planning. Dynamic imaging provides real-time evaluation of the process and can uncover any secondary causes of entrapment, such as coexistent osseous spurs or large sesamoids, foreign bodies, and soft-tissue masses or fluid collections. Therapeutic intervention such as local steroid injection can be guided with US (18,19).
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Figure 29a. Normal and abnormal pulleys. Arrow = flexor pollicis longus tendon. (a) Axial US scan shows a normal pulley (NP). (b) Axial US scan of a patient with trigger thumb shows a thickened pulley (P).
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Figure 29b. Normal and abnormal pulleys. Arrow = flexor pollicis longus tendon. (a) Axial US scan shows a normal pulley (NP). (b) Axial US scan of a patient with trigger thumb shows a thickened pulley (P).
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Figure 30. Trigger thumb. Left: Axial US scan of the metacarpophalangeal joint of the left thumb shows focal thickening of the flexor pollicis longus tendon (arrows). Right: Axial US scan of the metacarpophalangeal joint of the right thumb shows a normal tendon (arrows).
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Conclusions
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US has evolved as a reliable adjunct to clinical examination in evaluation of the UCL of the thumb. It provides a safe, simple, and effective method of assessing the ligament and its supporting structures at the bedside.
Other conditions involving this region may also be easily diagnosed. The clinician can therefore swiftly initiate a management strategy, with resultant improved patient care.
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Acknowledgments
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The authors acknowledge Sarah Abate and Bob Combs, Media Center, University of Michigan Department of Radiology.
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Footnotes
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Abbreviations: UCL = ulnar collateral ligament
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References
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- Hergan K, Mittler C, Oser W. Pitfalls in sonography of the gamekeepers’ thumb. Eur Radiol 1997; 7:65–69.[CrossRef][Medline]
- Harper MT, Chandnani VP, Spaeth J, Santangelo JR, Providence BC, Bagg MA. Gamekeeper thumb: diagnosis of ulnar collateral ligament injury using magnetic resonance imaging, magnetic resonance arthrography and stress radiography. J Magn Reson Imaging 1996;6(2):322–328.[Medline]
- Giele H, Martin J. The two-level ulnar collateral ligament injury of the metacarpophalangeal joint of the thumb. J Hand Surg [Br] 2003;28(1):92–93.
- Jones MH, England SJ, Muwanga CL, Hildreth T. The use of ultrasound in the diagnosis of injuries of the ulnar collateral ligament of the thumb. J Hand Surg [Br] 2000;25(1):29–32.[CrossRef][Medline]
- Hergan K, Mittler C, Oser W. Ulnar collateral ligament: differentiation of displaced and nondis-placed tears with US and MR imaging. Radiology 1995;194:65–71.[Abstract/Free Full Text]
- O’Callaghan BI, Kohut G, Hoogewoud HM. Gamekeeper thumb: identification of the Stener lesion with US. Radiology 1994;192:477–480.[Abstract/Free Full Text]
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Abstract
LEARNING OBJECTIVES FOR TEST...
