MRI of the hand and fingers.

REVIEW ARTICLE

MRI of the Hand and Fingers Abhijit Datir, MD, FRCR Abstract: Injuries of the hand and fingers occur commonly in professional athletes as well as weekend warriors. Magnetic resonance imaging plays a vital role in the evaluation of these injuries for accurate diagnosis, preoperative planning, potential complication, and follow-up during rehabilitation. A detailed analysis of these smaller structures necessitates optimal imaging quality coupled with comprehensive knowledge of the imaging anatomy. In this article, we discuss technical aspects and normal anatomy of hand and fingers imaging on magnetic resonance imaging. This section is followed by discussion of soft tissue and osseous injuries including mechanism of injury, clinical presentation, and imaging findings. Key Words: anatomy, fingers, hand, magnetic resonance imaging, sports injuries (Top Magn Reson Imaging 2015;24: 109–123)

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ports-related injuries of the hand and fingers are not uncommon, especially in professional athletes, competitive amateurs, and weekend warriors. Sporting activities that are at higher risk for hand and fingers injuries include skiing, biking, skating, football, and gymnastics.1–3 Magnetic resonance imaging (MRI) continues to be the optimal imaging technique for detailed assessment of the hand and fingers. With everevolving MRI sequences and improved understanding of the imaging anatomy of smaller structures such as hand and fingers, there is a high level of expectation for accurate diagnosis from the referring physician. In sports medicine, the athletes and the caring physicians including the orthopedists, physiatrists, and internists rely heavily on detailed imaging, not only to confirm the clinical suspicion but also to assess the extent of tissue damage, plan management, guide rehabilitation, and thereby limit disability. This has been made possible with increasing availability of high-field strength 3.0-T magnets and recent advances in radiofrequency gradients, extremity coil design, and pulse sequences for smaller joints. The importance of clear understanding of the normal anatomy of the hand and fingers cannot be overemphasized. While an exhaustive description of the normal imaging anatomy of the hand and fingers is beyond the scope of this article, we present a concise approach to the MRI anatomy of the hand and fingers that would frequently suffice in routine interpretation of sports injuries. In addition, we discuss MRI of common and uncommon sports injuries of the hand and fingers.

IMAGING TECHNIQUE Image quality is of paramount importance in the imaging of small parts, including hand and fingers. Excellent image quality can be achieved using 1.5-T magnets with the application of dedicated extremity coil, small field of view, and thin slice sections. Higher-field magnets (including 3.0 and 7.0 T) have the ability From the Musculoskeletal Division, Department of Radiology & Imaging Sciences, Emory University Hospital, Atlanta, GA. Reprints: Abhijit Datir, MD, FRCR, Emory Orthopedic & Spine Center, 59 Executive Park South, 4th Floor, Suite 4007, Atlanta, GA 30329 (e‐mail: [email protected]). The author declares no conflict of interest. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.

to produce images that are both high in signal-to-noise and contrast-to-noise ratios. This allows imaging at higher spatial resolution and with thinner slice thickness as compared with the 1.5-T magnets.4

Coil Selection and Patient Positioning5 A wide range of coils is available for the imaging of the hand and fingers. Dedicated flat or circumferential coil systems should be used to obtain uniform signal intensity (Figs. 1A, B). Flat coils allow more flexibility for positioning and motion study.6 Digit or small loop coils, although expensive, are excellent for the evaluation of individual joints and fingers (Fig. 1C). Patient positioning needs particular attention to avoid motion artifact and image degradation. In most patients, a satisfactory position can be achieved with arm at the side and the hand in comfortable position (pronation or supination) (Fig. 2A). Alternatives such as prone position with arm above the head can also be used, especially in larger patients and children (Fig. 2B). Also, other factors such as coil type, software, and need for motion studies should be taken into consideration. The hand should be supported with pads or bolsters to reduce motion, unless motion studies are being considered.

Technical Parameters In general, a small field of view (8–12 cm) is adequate for optimal imaging of hand and fingers with both flat and volume coils. An image matrix of 256 512 with 1- to 2-mm sections and 1 acquisition is commonly used. For volumetric and 3-dimensional (3D) imaging, thinner sections (0.6–1 mm) with 2 acquisitions can be used.

Pulse Sequences Initial scout images are obtained in coronal and sagittal planes (spin echo [SE]; repetition time = 400–500 milliseconds; echo time = 10–20 milliseconds) including the wrist and hand. Depending on the area of interest and clinical indication, the sequences and imaging planes are planned. At most institutions, conventional SE T1-weighted or proton-density (PD)–weighted and turbo or fast SE T2-weighted sequences with fat suppression are used. Alternatively, fluid-sensitive sequences such as short tau inversion recovery (STIR) can also be used. Gradient echo (GRE) sequences with 2D or 3D technique can be used with thin sections (0.6–1 mm) to allow for reformatting in any image plane. This is particularly useful in the evaluation of ligamentous, capsular, and articular anatomy. The use of gadolinium-enhanced contrast imaging is usually not required for routine evaluation of sports injuries and is usually reserved as a problem-solving tool, if necessary.7

NORMAL IMAGING ANATOMY The anatomy of the hand and fingers can be conveniently understood from imaging standpoint by dividing them in various sections as below. Normally, the tendons show hypointense signal on most sequences, whereas the muscles are intermediate in signal intensity. Occasionally, magic angle effect may cause spurious intermediate to high signal in the tendons at certain locations and should be kept in mind.

Topics in Magnetic Resonance Imaging • Volume 24, Number 2, April 2015

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FIGURE 1. Coils: (A) circumferential, (B) flat, and (C) small loop coils for MRI of the hand and fingers.

Anatomy of the Hand8,9 Thenar Eminence The thenar compartment anatomy of the hand is best appreciated in axial and coronal planes. It is composed of 5 myotendinous structures, including (from dorsal to ventral) first dorsal interosseous, adductor pollicis, flexor pollicis longus (FPL), abductor pollicis brevis, and opponens pollicis (Fig. 3). The adductor pollicis tendon fibers insert on the ulnar sesamoid of the thumb, whereas radial sesamoid provides attachment to the abductor/ opponens pollicis tendon fibers. The adductor pollicis is the deep layer of the thenar eminence and arises by 2 distinct heads, transverse and oblique, which ultimately converges to a short tendon that attaches to the ulnar sesamoid. This spatial relationship of the adductor pollicis attachment to the ulnar capsule of the thumb has clinical significance in sports injury, as described later in this article. The FPL tendon courses between the adductor pollicis and the abductor pollicis in its proximal course and through the space between the ulnar and radial sesamoids distally.

Palmar Hand and Hypothenar Eminence The palmar aspect of the midhand contains the flexor tendons (superficialis and profundus), the lumbricalis muscles attaching on the radial side of the flexor tendons, and superficially located neurovascular bundle. The interosseous muscles originate from adjacent metacarpals and are located deep to the extensor tendon (Fig. 4). The hypothenar eminence is composed of 3 muscles, namely, opponens digiti minimi, abductor digiti minimi, and flexor digiti minimi brevis. The opponens digiti minimi and the flexor digiti minimi brevis originate from the flexor

retinaculum of the wrist and the hook of the hamate, whereas the abductor digiti minimi originates from the pisiform. The flexor digiti minimi brevis and the abductor digiti minimi share a combined insertion on the fifth proximal phalanx, and opponens digiti minimi inserts on the fifth metacarpal proximally (Fig. 5).

Dorsum of the Hand The dorsum of the hand has significant anatomic variability because of tendinous multiplicity and the presence of connections between different tendons.10 The most frequent distribution pattern is as follows11: a single extensor indicis tendon located ulnar to the extensor digitorum tendon of the index finger, a single extensor digitorum tendon for the index and middle fingers, a double extensor digitorum tendon for the ring finger, no extensor digitorum tendon for the little finger, and a double extensor digit minimi tendon for the little finger (Fig. 6A). The extensor tendons have longitudinal splitting that increases mediolateral independent motion of mainly the second and fifth fingers. Closer to the metacarpophalangeal (MCP) joint, the extensor tendons are connected to each other in the dorsum of the hand by intertendinous connections (ie, juncturae tendinum) (Fig. 6B).12 These structures are oriented perpendicular to the extensor tendons and help to redistribute their force. These also limit independent flexion and extension of fingers by stabilizing the MCP joints.13

MCP Joint of the Thumb14 The MCP joint of the thumb is formed between the metacarpal head and the base of the first proximal phalanx along with 2 sesamoid bones. The main collateral and the accessory collateral

FIGURE 2. Patient positioning. A, Supine with arm at the side and (B) prone with arm above the head.

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MRI of the Hand and Fingers

FIGURE 3. Anatomy of the thenar eminence: axial and coronal PD-weighted MR images showing (A) spatial relationship of the muscles of the thenar eminence (white arrow = FPL); (B) distal insertion of the adductor pollicis and abductor pollicis brevis/opponens pollicis (dotted white arrow) on ulnar and radial sesamoids (white arrows), respectively, with FPL tendon (black arrow) positioned between the sesamoids; and (C) proximal course of the FPL tendon (white arrow) between the adductor pollicis and abductor pollicis brevis/opponens pollicis. DI indicates dorsal interosseous; AdP, adductor pollicis; AbP, abductor pollicis brevis; OP, opponens pollicis.

ligaments reinforce the MCP joint capsule. The portion of the capsule that accommodates the sesamoid is referred to as the intersesamoid ligament (also known as “volar plate of the MCP joint”). The FPL tendon is intimately connected to the volar plate and runs between the 2 sesamoids as described above. The dorsum of the joint is in contact with the tendinous attachments of the extensor pollicis longus (EPL) and brevis, also known as long muscles of the thumb (Fig. 7).

Lesser MCP Joints15,16 The lesser MCP joints are unicondylar joints that allow a degree of rotation and radial/ulnar deviation as well as flexion/ extension. The joint capsule is reinforced by the collateral ligamentous complex, which is composed of 2 bands, the main and the accessory collateral ligaments. These are optimally demonstrated on axial images with the joint flexed, or on coronal images with the joint extended. The volar plate is firmly attached to the base of the proximal phalanx and along with the accessory collateral ligaments stabilizes the metacarpal head during flexion. A deep transverse metacarpal ligament connects the adjacent volar plates and is optimally seen on axial images with the joint extended. The extensor hood is made of the sagittal bands, the transverse fibers, and the extensor tendons. The sagittal bands are thin bands extending from the extensor tendon dorsally to the junction of the volar plate and deep transverse metacarpal ligament (Fig. 8).

The transverse fibers form a triangular lamina distal to the sagittal bands and extend between the extensor and interosseous tendons.

Anatomy of the Fingers and Thumb Flexor Mechanism The long flexor tendons of the fingers and thumb include the flexor digitorum superficialis (FDS), the flexor digitorum profundus (FDP), and the FPL. Each finger receives attachment from the FDS and FDP tendons, whereas the thumb receives only the FPL tendon. Proximal to the metacarpal head, the FDS tendon lies superficial to the FDP tendon (Fig. 9A). Each tendon of the FDS splits into 2 slips at the level of the proximal phalanx to allow passage of the FDP tendon. Distal to this point, the FDS tendon lies dorsal to the FDP tendon. The FDS splits down to insert on the middle phalanx, whereas the FDP inserts on the distal phalanx (Fig. 9B). The flexor tendons of the hand and wrist are divided into 5 anatomic zones (zones I–V) from distal to proximal, as described in Table 1 (Fig. 9C).17,18 The flexor tendons are closely fixed to the phalanges within a fibro-osseous tunnel that is lined by a synovial sheath. The fibroosseous tunnel is formed by the palmar surface of the phalanges and their joint capsules, along with the finger pulley system. The finger pulley system is an intricate mechanism composed of focally thickened retinacular areas of the flexor tendon sheaths.19,20 There are 8 functional pulleys in each finger, extending

FIGURE 4. Anatomy of the palmar aspect of the midhand. A, Axial PD-weighted MR image at the level of midmetacarpal showing FDS (S) and profundus (P) tendons with lumbricalis muscle (black arrow) inserting on the radial aspect of these tendons. The dorsal (short white arrow) and palmar interosseous muscles are seen along the dorsal aspect of the flexor tendons and between the metacarpals with neurovascular bundle in the most superficial location (dotted arrow). B, Sagittal PD-weighted MR image showing longitudinal course and relationship of the flexor tendons. © 2015 Wolters Kluwer Health, Inc. All rights reserved.


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FIGURE 5. Anatomy of the hypothenar eminence. A, Axial PD-weighted MR image showing hypothenar muscles including the abductor digiti minimi (ADM), the opponens digiti minimi (solid white arrow), and the flexor digiti minimi brevis (dotted white arrow). Note the common origin of the opponens digiti minimi and the flexor digiti minimi brevis from the flexor retinaculum of the wrist (black arrow). B, Axial PD-weighted MR image showing the distal insertion of the opponens digiti minimi on distal aspect of the fifth metacarpal (white arrow). The abductor digiti minimi and flexor digiti minimi brevis are seen together distally (black arrow). C, Coronal PD-weighted MR image showing proximal origin of the abductor digiti minimi (long white arrow) from the pisiform (P) and distal common insertion with the flexor digiti minimi brevis (short white arrow) on proximal phalanx of the thumb (black arrow).

from the volar plate of the MCP joint to the base of the distal phalanx. These include 5 annular pulleys (A1–A5), which are stronger and functionally more important than the 3 cruciform pulleys (C1– C3). The 5 annular pulleys are identified based on their location, that is, A1, most proximal, spanning the volar plate of the MCP joint and inserting on proximal phalangeal base; A2, extending from the proximal phalangeal base to the proximal phalangeal neck; A3, at the proximal interphalangeal (PIP) joint level; A4, at the level of mid-portion of middle phalanx; and A5, at the distal interphalangeal (DIP) joint level. The cruciform pulleys further stabilize the finger pulley system and are designated as C1, located between A2 and A3; C2, located between A3 and A4; and C3, located between A4 and A5. The main function of the pulley system is to stabilize the flexor tendon during finger flexion by keeping the tendons closely apposed to the phalanges. The cruciform pulleys are designed to permit deformation of the tendon sheath during flexion without impingement on the tendon proper.21,22 Normal A2 and A4 pulleys are commonly depicted on conventional T1weighted SE and fast-spoiled GRE sequences (Fig. 9D), but A3 and A5 are difficult to visualize because of their small size and lack of osseous insertion.

and DIP joints and includes the interosseous and lumbricalis muscles. The extrinsic muscle group acts to extend MCP, PIP, and DIP joints and includes the extensor digiti minimi, extensor digitorum, and extensor indicis. For the ease of understanding and accurate lesion localization, the Verdan system17,18 is used for topographic classification of the extensor tendon anatomy, as summarized in Table 2 (Fig. 10A). At the level of the midproximal phalanx, the extensor tendon trifurcates into a central slip and paired lateral slips (lateral bands) (Fig. 10B). The lateral bands of the extensor tendon intermingle with interosseous and lumbricalis tendons to form conjoint tendon, just proximal to the PIP joint. The central slips inserts onto the dorsal base of the middle phalanx (Fig. 10C). These are seen as thin, flat, and hypointense band-like structures that are difficult to differentiate from the joint capsules.

Interphalangeal Joint of the Thumb As other joints of the hand, interphalangeal (IP) joint capsule of the thumb is also reinforced by the main and accessory collateral ligaments as well as the volar plate. The FPL tendon passes over the volar plate to reach its insertion, whereas the EPL adhere to the joint capsule dorsally.

Extensor Mechanism The extension of the fingers at the level of PIP, DIP, and MCP joints is achieved through the extrinsic and intrinsic muscle groups. The intrinsic muscle group primarily extends the PIP

PIP Joint The PIP joint is a bicondylar hinge joint stabilized by surrounding soft tissues, particularly the collateral ligaments and

FIGURE 6. Anatomy of the dorsum of the hand. A, Axial T1-weighted MR image showing extensor tendons of the index (I), middle (M), ring (R), and little (L) fingers with most common distribution pattern, that is, a single extensor digitorum tendon for index (I) and middle (M) fingers, and 2 extensor digitorum tendons for ring (R) finger (solid arrows), an extensor indicis tendon on ulnar side of the index finger tendon (broken arrow), 2 extensor digiti minimi tendons for little finger (arrowheads). B, Axial T1-weighted MR image near the level of the MCP joints showing intertendinous connections (black arrows) between the extensor tendons (white arrows), also known as juncturae tendinum.

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FIGURE 7. Anatomy of the MCP joint of the thumb: A, axial oblique T1-weighted MR image showing location and attachments of the main (arrows) and the accessory (arrowheads) collateral ligaments. B, Same image as A, showing the intersesamoid ligament (broken arrow) intimately contacting the FPL tendon (solid arrow) between the 2 sesamoids (S). The insertion of the adductor pollicis tendon (black arrowhead) on ulnar sesamoid and abductor pollicis tendon (white arrowhead) on radial sesamoid is also shown. C, Coronal fat-saturated PD-weighted MR image showing the UCL (arrowhead) and closely apposed adductor pollicis longus aponeurosis (solid arrow). Similar spatial relationship exists between the RCL and the superficial tendon of the adductor pollicis brevis (broken arrow). D, Sagittal PD-weighted MR image showing dorsal extensor tendons of the thumb including the EPL (solid arrow) and brevis (broken arrow) at the level of MCP joint.

the volar plate. The collateral ligament complex is composed of the main (or proper) and accessory collateral ligaments and is optimally visualized on coronal images. The volar plate is a thick, fibrocartilaginous structure that forms the palmar aspect of the PIP joint capsule. It is attached to the proximal phalanx by 2 lateral bands called the “check rein” ligaments and extends distally to attach loosely to the volar aspect of the middle phalanx. This anatomic arrangement permits the volar plate to retract from the base of the middle phalanx during joint flexion. The volar plate also acts to prevent the hyperextension of the PIP joint and is best visualized on sagittal images. The extensor apparatus, the flexor tendons, and the reticular ligaments maintain the dynamic stability of the PIP joint. The extensor apparatus provides dorsal stability to the PIP joint and provides a central slip that inserts on the dorsal tubercle of the middle phalanx and the medial and lateral slips that are connected by the reticular ligaments as detailed previously (Fig. 11).

DIP Joint The DIP joint is formed by the junction of the base of the distal phalanx with the middle phalanx head. Thick main and

accessory collateral ligaments reinforce the joint capsule laterally (Fig. 12). The volar plate provides for volar stability and serves as a floor for the FDP tendon. Proximally, the plate attaches to the middle phalanx; however, there are no “checkrein” ligaments as seen in PIP joint, so hyperextension is permitted. The fibrous tunnel of the flexor tendons (the A5 pulley at the level of the DIP joint) extends from the tendon to the volar plate and is best seen in the axial plane. The FDP tendon fans over the entire width of the joint, before inserting into the base of the distal phalanx. The dorsum of the DIP joint has no reinforcing ligament, although the terminal part of the extensor apparatus of the finger serves as a reinforcement firmly adhering to the capsule between the collateral ligaments.

IMAGING OF SPORTS INJURIES Injuries of the hand and fingers are common, especially in the athletic population, and account for up to 20% of emergency department visits.23 As emphasized earlier, a detailed knowledge of the normal anatomy is essential for accurate diagnosis and characterization of lesions. In this section, we review imaging features of various sports injuries involving hand and fingers. For better

FIGURE 8. Anatomy of the lesser MCP joint. A, Diagrammatic representation for detailed anatomy of the sagittal band. B, High-resolution thin (1-mm) slice isometric PD-weighted MR image showing complex soft tissue anatomy with extensor tendon (white arrow), sagittal bands (black arrows), interosseous tendons (curved black arrow), deep transverse metacarpal ligament or DTML (arrowheads), and lumbricalis muscle (broken white arrow). Note the superficial location of lumbricalis muscle to DTML. ED indicates extensor digitorum; MCL, main collateral ligament; ACL, accessory collateral ligament; IT, interosseous tendon; DTML, deep transverse metacarpal ligament; LT, lumbricalis tendon. © 2015 Wolters Kluwer Health, Inc. All rights reserved.


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FIGURE 9. Flexor tendon anatomy. Axial (A) and sagittal (B) T1-weighted MR image showing relationship, course, and insertion of the FDS (S, short white arrow) and FDP (P, long white arrow) tendons. C, Schematic representation of the flexor tendon zonal anatomy. D, Axial T1-weighted MR image showing A2 pulley (arrowheads) encasing the FDS (short arrows) and FDP (long curved arrow).

understanding, the section has been divided into ligament, tendon, and osseous injuries.

Collateral Ligament Injury of the MCP, PIP, and DIP Joints Ulnar Collateral Ligament of the Thumb MCP Joint (Gamekeeper’s Thumb and Stener Lesion) The term “gamekeeper’s thumb” was initially coined by Campbell24 to describe a chronic repetitive injury of the ulnar collateral ligament (UCL) of the thumb MCP joint and has been reported to constitute up to 86% of all injuries at the base of the thumb. However, in current literature, it is used to describe both

acute and chronic injuries of the UCL of the thumb. Some authors reserve this term for chronic UCL injuries and refer to acute UCL injuries as “skier’s thumb.”25 The primary mechanism of this type of injury is an abrupt radial stress to the UCL as initially described in Scottish gamekeepers. A similar mechanism of injury is seen in skiers when the thumb is in adduction during fall and thereby resulting in a radial or valgus stress. The classic location of UCL injury in gamekeeper’s thumb is at the distal attachment, with a discontinuous but otherwise normal location of the ligament. The term “Stener lesion” is used when the UCL is retracted proximally and displaced superficial to the adductor aponeurosis.26 This prevents the primary healing of UCL injury with conservative management, as UCL is no longer in contact with the

TABLE 1. Anatomic Zones of the Flexor Tendons Zone

Description

Zone I

Extends from the distal insertion of the FDS on the middle phalanx to the distal insertion of the FDP on the distal phalanx and contains the FDP tendon Also known as “no man’s land” and extends from the A1 pulley to the distal insertion of the FDS Extends from the distal part of the flexor retinaculum at the carpal tunnel to the proximal part of the A1 pulley and contains the lumbricalis origins from the FDP tendons Contains the flexor tendons within the carpal tunnel Extends from the musculotendinous junction of the flexor group to the proximal aspect of the carpal tunnel

Zone II Zone III Zone IV Zone V

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TABLE 2. Anatomic Zones of the Extensor Tendons Region Zone Zone I Zone II Zone III Zone IV Zone V Zone VI Zone VII Zones VIII-X

Fingers

Thumb

DIP region Middle phalanx PIP region Proximal phalanx MCP region Dorsum of the hand Wrist extensor compartment

IP region Proximal phalanx MCP region Metacarpal Wrist extensor compartment

Extrinsic extensor muscles

donor site and therefore needs surgical repair. Patients may present with swelling, ecchymosis, and decreased range of motion at the first MCP joint on ulnar side.

MRI Findings Normally, the UCL consists of the UCL proper and the accessory UCL, which are taut reciprocally during flexion and extension. The adductor pollicis longus muscle has transverse and oblique heads that together form an aponeurosis that attaches at the ulnar aspect of the proximal phalanx, superficial to the UCL. In acute UCL injuries, the UCL is bunched up and proximally retracted and lying either superficial (ie, Stener lesion) or deep to the adductor aponeurosis (Fig. 13). This appearance has been referred to as “yo-yo on a string,” with adductor aponeurosis representing the “string” and the retracted UCL representing the “yo-yo.”27

Radial Collateral Ligament of the Thumb MCP Joint Although UCL injuries of the thumb MCP joint are described more often, the radial collateral ligament (RCL) injuries do occur with high frequency, accounting for 40% to 42% of all collateral ligament repairs at the thumb (Fig. 14).28 The RCL injury coupled with the unopposed dynamic force of the adductor pollicis has been described to increase the likelihood of significant joint instability and eventually degenerative joint disease if left untreated.29

Collateral Ligament of the Lesser MCP Joints Collateral ligament injuries of the lesser MCP joints are considered to be rare as compared with the thumb. These are much more common on the radial side and occur because of lateral deviation of the flexed joint. Delaere et al30 reported these to commonly involve the RCL of the fourth and fifth fingers and UCL of the index finger. The lower incidence of RCL injury in the index finger has been explained by the shielding effect from ulnar stresses by the third through fifth fingers that buttress the index finger. Conversely, the fifth finger has higher incidence of RCL injury due to lack of shielding from ulnar-sided forces by other digits. The middle finger has an equal incidence of RCL and UCL tears. Patients with collateral ligament injury may complain of focal pain and joint instability while grasping objects. In the acute setting, laxity of the MCP joint in full extension without a clear end point is considered to suggest complete collateral ligament tear. These patients are often treated with direct surgical repair with suture anchors or reconstruction using autologous grafts.31 On the other hand, patients without MCP joint laxity are treated conservatively with joint immobilization for 3 to 6 weeks.

MRI Findings Magnetic resonance imaging may show frank detachment, thickening with increased signal on fluid-sensitive sequence, or joint fluid/edema replacing the collateral ligament in acute setting (Fig. 15). Chronic ligamentous injury may be seen as ligamentous

FIGURE 10. Extensor tendon anatomy. A, Schematic representation of the extensor tendon zonal anatomy. B, Axial and (C) sagittal T1-weighted MR images showing relationship and insertions of the central slip (black arrow) and lateral slips (white arrows). © 2015 Wolters Kluwer Health, Inc. All rights reserved.


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FIGURE 11. Anatomy of the PIP joint. A, Axial T1-weighted MR image showing the location of the collateral ligaments (short solid arrows), the accessory collateral ligaments (short broken arrows), the volar plate (arrowhead), the central slip (long broken arrow), and the lateral slips (solid arrows with round ends) of the extensor mechanism. B, Coronal T1-weighted MR image showing position and attachments of the main collateral ligaments (arrowheads). C, Sagittal T1-weighted MR image showing the volar plate (solid arrow) and its capsular attachments at PIP joint. Central slip (broken arrow).

thickening and fibrosis. Pfirrmann et al32 have reported a sensitivity of 66.7% and specificity of 90.9% for detection of lesser MCP joint collateral ligament injuries on conventional MRI, whereas magnetic resonance (MR) arthrography has been described to show these injuries with higher sensitivity (75%) and specificity (97.7%).

Collateral Ligament of the IP, PIP, and DIP Joints Commonly used term “sprained finger” usually means a collateral ligament or volar plate injury, with the index finger being the most commonly involved. The mechanism of collateral ligament injury at the level of PIP or DIP joint involves an abducting or adducting force applied to the extended finger. The spectrum of injuries and corresponding MRI findings (Fig. 16) are described in Table 3.33

Volar Plate Injury of the PIP Joint These usually result from hyperextension of the PIP joint or rotational-longitudinal compression leading to instability in the sagittal plane and thereby major articular instability. Depending on the degree of dorsal articular displacement, the volar plate injuries are classified into 3 types as below.34,35 The treatment is

usually conservative in all cases, except unstable type III that typically needs open reduction and internal fixation. type I—avulsion from the base of the middle phalanx resulting in PIP joint hyperextension (“swan neck deformity”) or less commonly from the proximal phalanx insertion with resultant flexion contracture of the PIP joint (“pseudoboutonniere deformity,” if left untreated);33 type II—more extensive peri-articular soft tissue involvement resulting from volar plate avulsion and a major split between the components of the collateral ligament complex; this usually results in higher degree of instability compared with type I, with dorsal subluxation or dislocation of the middle phalanx; and type III—characterized by fracture-dislocation of the volar base of the middle phalanx; these are classified into stable (40% articular surface involvement with collateral ligament attached to the fracture fragment).

MRI Findings Magnetic resonance imaging usually shows heterogeneous signal intensity involving the volar plate with thickening and

FIGURE 12. Anatomy of the DIP joint. A, Coronal T1-weighted MR image showing the collateral ligaments (white arrows) coursing from the head of the middle phalanx proximally to the laterovolar tubercles of the distal phalanx. B, Axial fat-suppressed PD-weighted MR image showing the collateral ligaments (white arrows), posterior extension of the accessory collateral ligaments (black arrowheads), and broad-based attachment of the distal extensor tendon (white arrowhead).

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FIGURE 13. Acute UCL injury of the thumb MCP joint. Coronal PD-weighted sequences without (A) and with (B) fat suppression showing torn and proximally retracted UCL (arrow) with intact overlying adductor aponeurosis (arrowhead), suggestive of “gamekeeper’s thumb.” C, Coronal fat-suppressed PD-weighted image showing torn and balled-up UCL (arrow) positioned superficial to the adductor aponeurosis (arrowhead), consistent with the diagnosis of Stener lesion.

contour irregularities on T1- and T2-weighted sequences (Fig. 17). Depending on the type of injury, a degree of surrounding edema and fracture fragment can also be seen.

Sagittal Band Injury of the MCP Joint Injury to the sagittal band occurs more commonly in the setting of degenerative lesions resulting from rheumatoid arthritis.36 In sports-related traumatic injury to the sagittal band, typically a single digit is affected, whereas multiple digit involvement is usually seen in congenital setting in pediatric population. The radial fibers are more commonly affected than the ulnar side because of thinner and longer morphology. Similarly, the middle finger is most commonly involved owing to its especially thin and long sagittal band and prominent metacarpal head. The mechanism of injury may involve direct blow and sudden forced flexion of the MCP joint, as seen with high frequency in boxers and colloquial FIGURE 14. Acute RCL injury of the thumb MCP joint. Oblique coronal fat-suppressed PD-weighted image showing proximal tear of the RCL with detachment from the metacarpal head (arrow).

FIGURE 15. Ulnar collateral ligament injury of the lesser (fifth) MCP joint. Coronal STIR image at the level of MCP joint shows thinned and proximally torn UCL (arrow) with minimal associated fluid signal intensity.

FIGURE 16. Complete collateral ligament tear of the first IP joint of the thumb. Coronal fat-suppressed PD-weighted image with completely torn RCL (arrow) at the level of the thumb IP joint, with surrounding fluid and edema.



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TABLE 3. Collateral Ligament Injury Grading Based on MRI Findings Type of Injury

MRI Findings

Sprain Partial tear

Intact ligament with surrounding edema Increased intrinsic ligament signal on fluid-sensitive sequences but otherwise intact ligament Complete tear Intrinsic signal abnormality with detached, discontinuous or thickened ligament due to edema or hemorrhage

termed “boxer’s knuckle.”37 Spontaneous nontraumatic rupture of the sagittal band has also been described. Patients usually present with pain, swelling, sagittal band tenderness, extensor tendon instability, and limited MCP joint extension. Acute injuries are usually treated with closed extension splinting, whereas direct repair with or without graft is reserved for patients who fail splinting or those with persistent subluxation and weak extension.

MRI Findings The diagnosis of pulley rupture can be made in a correct clinical setting with nonvisualization of the pulley, best seen in the axial plane. An indirect sign of pulley injury (“bowstring sign”) has been described with detection of abnormal increased signal on fluid-sensitive sequence between the flexor tendon and adjacent bone, best depicted on sagittal plane (Fig. 19).41 Also, the degree and distribution of tendon displacement can suggest the severity and localization of pulley lesion.

Extensor Tendon Injury The extensor tendons of the hand and fingers are particularly prone to injuries because of their superficial location. Magnetic resonance imaging helps in identifying the severity of tendon injury, differentiating low-grade lesion from high-grade lesion and partial tear from complete tear. Extensor tendon injuries are classified as open (ie, laceration or penetrating injury resulting in disruption of the overlying skin and soft tissues) and closed (ie, injuries with intact overlying soft tissues).

Open Injuries MRI Findings Attention should be given to the proximity of site of injury from extensor tendon as well as to the involvement of deep and superficial fibers (Fig. 18). Typically, the traumatic injury involves deep and superficial fibers and occurs several millimeters radial to the extensor tendon. Spontaneous disruption is characterized by involvement of only the superficial fibers in close proximity to the extensor tendon. Drape et al38 reported T2*-weighted images to be more accurate than T1-weighted (with or without contrast enhancement) images for normal and pathologic sagittal bands.

Flexor Pulley Injury The A2 pulley is the strongest and also the most frequently injured pulley. The usual pattern of pulley injury follows from A2 pulley to subsequently involve A3, and then the A4 pulleys. The A1 and A5 pulleys are rarely injured.39 The diagnosis of pulley lesion remains challenging with pain, swelling, and limited range of motion, making the physical examination difficult. The patient may report sudden onset of pain that coincides with a slip or forceful maneuver, and sometimes an audible pop may be heard. Rock climbers are particularly prone to pulley injuries because of the tremendous load placed on the pulley system. The traditional rock-climbing grip (described as “crimp position”) involves PIP joint hyperflexion, and DIP and MCP joint hyperextension during which the climber grips tightly and levers upward. This type of injury is often referred to as “climber’s finger.”40

Usually the result of lacerations, these injuries predominate at the levels of the middle phalanx (zone II), proximal phalanx (zone IV), the MCP joint (zone V), and the dorsum of the hand (zone VI). In zone II, because of the radial and ulnar position of the tendons, a simple laceration rarely transects the extensor apparatus. Similarly, in zones III and IV, because of the circumferential orientation and interconnections, complete laceration and retraction are uncommon.42 In zone V (at the level of MCP joint), the extensor tendon injury is commonly seen in human bite and may be associated with extensor hood injury (especially the sagittal band). Because of their very superficial location at the dorsum of the hand (zone VI), an innocuous injury may result in multiple tendon lacerations.

MRI Findings A thorough assessment of the entire extensor tendon and associated structures (such as joint capsule and sagittal band) is of paramount importance from the management perspective. These injuries are best evaluated with combination of sagittal and axial images. A complete assessment should include characterization of tendon lesion margins, adjacent soft tissue defect, and associated sagittal band, capsular, or osseous injury. A detailed description of the torn ends with intervening gap and precise localization should be provided in case of tendon rupture.

Closed Injuries These include injury to the central slip and the terminal tendon that inserts into the dorsal osseous prominences of the middle

FIGURE 17. Volar plate injury. Sagittal T1-weighted (A) and fat-suppressed PD-weighted (B) images showing torn and proximally displaced volar plate (arrow) consistent with type III injury.

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FIGURE 18. Sagittal band injury. Schematic representation showing (A) normal sagittal band with superficial and deep layers, (B) spontaneous rupture that usually occurs in close proximity to the extensor tendon and involving only the superficial fibers, (C) traumatic rupture that often involves both superficial and deep fibers away from the extensor tendon. Coronal PD-weighted sequences without (D) and with (E) fat suppression showing thickened and heterogeneously hyperintense sagittal band with surrounding rim of fluid/edema consistent with acute injury (arrows).

and distal phalanges, respectively. Because of the closed nature, these injuries are often missed or undertreated.

Mallet Deformity This results from injury at the level of zone I with disruption of the terminal extensor tendon attachment from the base of the distal phalanx. This is most commonly seen as a closed injury because of forced flexion of the DIP joint in an extended digit and can be seen with or without an avulsed bone fragment.43 Spontaneous disruption of the terminal extensor tendon has also been described. Four different types of mallet deformities have been described as shown in Table 4.44 Ultimately, failure of the extensor tendon results in unopposed DIP joint flexion. If left untreated, this results in a fixed flexion deformity of the DIP and hyperextension of the PIP joints (“swan neck deformity”) because of retraction of the extensor mechanism. From the treatment point of

view, the presence of an avulsed fracture fragment elicits better healing than the tendon avulsion alone. Various surgical options exist for injuries with failed splinting or more than 40 degrees of extensor lag.

MRI Findings Sagittal and axial planes are best suited for evaluation of the extensor tendon injuries. The findings include fixed DIP joint flexion, tendon discontinuity, and proximal retraction, with or without osseous avulsion fragment (Fig. 20).

Boutonniere Deformity45,46 This term is derived from the French for “buttonhole.” This type of deformity usually results from forced PIP joint flexion, palmar dislocation of the middle phalanx, or a direct blow to the dorsum of the hand. Immediately following trauma, the ability

FIGURE 19. A2 pulley lesion. Axial (A) and sagittal (B) fat-suppressed PD-weighted sequences showing hyperintense signal at the expected location A2 pulley representing edema and fluid (arrows). No significant “bow stringing” is seen. Compare normal appearance of adjacent A2 pulley on axial sequence (arrowhead). © 2015 Wolters Kluwer Health, Inc. All rights reserved.


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TABLE 4. Types of “Mallet Deformity” of the DIP Joint Type I II III IV

Description Closed injury with or without small avulsion fracture Open laceration at or proximal to the DIP with loss of tendon discontinuity Open deep abrasion with loss of skin, subcutaneous cover, and tendon substance Subtype A Transepiphyseal plate fracture in children Subtype B Hyperflexion injury with fracture of 20%–50% articular surface Subtype C Hyperextension injury with fracture >50% articular surface with palmar subluxation of the distal phalanx

to extend the PIP joint is often preserved because of intact lateral bands, which serves as primary extenders of this joint. If left untreated, the lateral bands migrate to a volar position and then functions as PIP joint flexors rather than extenders. This allows the proximal phalangeal head and PIP joint to pop through the “buttonhole.” Closed extension splinting is the initial treatment choice, whereas extensor reconstruction is reserved for chronic deformity.

MRI Findings As in other extensor tendon injuries, sagittal and axial images remain the mainstay for the diagnosis. The diagnosis is established by tendon discontinuity or detachment from the middle phalanx, with or without avulsed fragment.

Flexor Tendon Injury Injury to the flexor tendon is relatively uncommon as compared with the extensor tendon. As for extensor tendon, these injuries are simply classified into open and closed types.

Open Injuries Laceration is the most common cause of flexor tendon injury and classically affects the midsubstance of the tendon rather that the osseous attachment site. The zone of laceration and involvement of particular flexor tendon dictates the clinical presentation. For distal laceration in zone I involving only the FDP tendon, the patient demonstrates loss of active DIP flexion, whereas the proximal laceration involving both the FDP and FDS tendons will

result in loss of flexion at both PIP and DIP joints. A possible lumbricalis muscle and/or neurovascular injury should always be considered with more proximal injuries involving zones III to V.47 The findings associated with tendon injury are best seen on fluid-sensitive sequences such as STIR, or fat-suppressed PDweighted sequence, whereas T1-weighted sequences provide detailed anatomic evaluation. Lacerations in zone II (from the A1 pulley to the distal insertion of the FDS) are the most frequent and carry the worst prognosis as scar tissue within the tendon sheath can often lead to adhesions and entrapment.48 Zone II was described by Bunnell as “no man’s land,” who cautioned against repairing flexor tendon injuries in this region.49 However, Verdan50 subsequently demonstrated that complete lacerations could be successfully treated by primary repair.

MRI Findings The utility of MRI in the diagnosis of partial and complete lacerations was described by Rubin et al.51 A complete laceration would be seen as a gap between the torn ends of the tendon with proximal retraction. Tears involving less than 50% of the total tendon area are defined as low-grade lesions, and those involving more than 50% are considered to be high-grade lesions. As the flexor tendons are less firmly attached to the adjacent bone, a greater degree of retraction is seen as compared with extensor tendon injury. Magnetic resonance imaging accurately determines the extent of torn tendon retraction and thereby helps in preoperative planning.

Closed Injuries These injuries include avulsion of the FDP and FDS tendon and are relatively less common than the open injuries. In addition to acute sports injury, a variety of chronic pathologic conditions that weakens the tendon have been implicated such as rheumatoid arthritis, osteoarthritis, or previous trauma.52 The most common type of closed flexor tendon injury of the finger is avulsion of the FDP tendon. This is caused by sudden hyperextension of the DIP joint during active flexion. This type of injury is most commonly seen in contact sports such as football, rugby, and flag football and usually involves the ring finger. This often occurs while grasping the jersey of an opposing player and is often referred to as the “jersey finger.”53 In acute setting, the injury is often overlooked as loss of active DIP flexion may be masked by pain and soft tissue swelling, leading to delayed diagnosis and management. Various types of FDP avulsions have been described as shown in Table 5.54 The type of injury has implication for

FIGURE 20. Mallet finger. A, Radiograph showing avulsion fracture at the dorsal aspect of the base of the distal phalanx with surrounding soft tissue swelling. B, T1-weighted and (C) fat-suppressed PD-weighted images showing acute tear of the terminal extensor tendon from the base of the distal phalanx with minimal retraction, that is, “mallet finger.”

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TABLE 5. Types of FDP Tendon Avulsion Injury Type I II III IV

Description With tendon retraction into the palm, often leading to disruption of the vascular supply With FDP tendon retraction to the PIP joint level, with or without small osseous avulsion fragment With large osseous avulsion fragment that limits FDP tendon retraction to the DIP joint level With osseous fragment and simultaneous avulsion of the tendon from the fragment

treatment; for example, type 1 injury needs prompt (7–10 days) surgical correction, whereas others are typically treated over several weeks. Isolated FDS tendon injuries are rare, as most injuries occur in conjunction with FDP injuries.55 With an isolated FDS avulsion, there is loss of active PIP joint flexion. The patient may present with palmar tenderness or a palpable palmar mass accompanying tendon retraction. Early surgical intervention is recommended as delay in treatment causes further proximal retraction of the torn tendon.

MRI Findings Magnetic resonance imaging helps to identify tendon rupture, measure the size of the gap between torn ends, and locate the proximal torn end (Fig. 21). A gap of more than 30 mm is treated with tendon graft rather than single suture. Drape et al56 found that axial T1-weighted SE and 3D GRE acquisitions are usually sufficient to evaluate the appearance of torn ends.

Osseous Injury Conventional radiography continues to remain the mainstay for primary diagnosis of acute osseous injury involving the hand and fingers. However, MRI offers better assessment of the associated soft tissue injury with exquisite details. Magnetic resonance imaging is usually reserved for evaluation of complex trauma with suspected soft tissue injury or evaluation of persistent pain


following successful fracture reduction. At many centers, it is commonly utilized for preoperative planning and assessment.

Fracture-Dislocation of the PIP Joint The mechanism of injury resulting in dislocation of the PIP joint is axial loading with resultant joint hyperextension.57 This usually causes dorsal or dorsolateral, and rarely volar dislocation, and is often seen in contact sports. The dorsal dislocation results in volar plate and accessory collateral ligament injury. Nonreducible dislocation can be secondary to entrapped volar plate, joint capsule, lateral band, or flexor profundus tendon. Lateral or volar dislocation of the PIP joint is usually due to injury to a single collateral ligament. The PIP joint fracture-dislocation can be simply classified as stable or unstable depending on less than or more than 40% middle phalangeal articular surface involvement, respectively.

Fracture-Dislocation of the MCP Joint Depending on direction of the displacement of distal osseous fragment, lesser MCP joint dislocation is classified as dorsal, lateral, and volar. Dorsal dislocation is the most common, whereas as volar dislocation is the least frequent. These can be also classified into simple (reduction possible under close manipulation) or complex (irreducible fracture-dislocation).33 As seen in PIP joint dislocation, irreducible MCP joint dislocation is often due to entrapped soft tissue component.

Fracture of the First Metacarpal Base Approximately 80% of the first metacarpal fractures occur at the base.58 It is important from the management point of view to identify whether the fracture is intra-articular or extra-articular.

FUTURE DIRECTIONS Currently, most imaging centers utilize 1.5- or 3.0-T magnets for imaging of the smaller structures such as hand and fingers. The use of 7.0-T magnets for imaging of the hand and fingers has been mainly for research purposes until now.59 Several articles have been published on utility of 7.0-T or higher-strength magnets for hand and wrist imaging.59,60 Although ultrahigh-field magnets such as 7 T allow for better signal-to-noise ratio, which in turn increases spatial resolution, there are several technical challenges. The use of an appropriate radiofrequency coil design is the most

FIGURE 21. Flexor digitorum profundus tear. A, Axial PD-weighted image showing absent FDP tendon (arrow) at the dorsal aspect of the split FDS tendon (arrowheads) and (B) sagittal PD-weighted image showing torn and proximally retracted FDP tendon (arrow) with fluid-filled gap (arrowhead). © 2015 Wolters Kluwer Health, Inc. All rights reserved.


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essential element in obtaining high-quality images at 7.0 T.60 With continued research, exact delineation of most anatomical structures is possible. The increased signal-to-noise ratio with 7.0-T magnets can be utilized to achieve faster data acquisition or higher resolution. Several sequences have been described for imaging on 7.0-T magnets including GRE with or without fat suppression, 3D GRE, and PD-weighted turbo SE.61–63 Also, cartilage and biochemical imaging with techniques such as spectroscopy, sodium imaging, dGEMRIC (delayed gadolinium-enhanced MRI of cartilage), and T2* mapping is being studied.63

CONCLUSIONS Imaging of sports injuries involving the hand and fingers needs high-quality imaging with detailed understanding of the relevant anatomy. With proper sequences and scanning technique, excellent images can be obtained that not only helps to make accurate diagnosis, but also helps in better patient care and rehabilitation. With advances in imaging technique and utilization of high-field magnets, imaging will continue to play an important role in the sports injuries of the hand and fingers. ACKNOWLEDGMENTS The authors thank Mark Lux and Kristen Smith, MRI technicians at Emory Orthopedic and Spine Center, for providing normal anatomy and patient positioning images. They also thank Jad Chamieh, research associate at Emory Orthopedic and Spine Center, for schematic diagrams. REFERENCES 1. Rettig AC. Epidemiology of hand and wrist injuries in sports. Clin Sports Med. 1998;17:401–406. 2. Patel D, Dean C, Baker RJ. The hand in sports: an update on the clinical anatomy and physical examination. Prim Care. 2005;32:71–89.

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[Congenital windblown hand position of the fingers].

Effect of ambient temperature on the thermal profile of the human forearm, hand, and fingers.

Factors influencing final range of motion in the fingers after fractures of the hand.

MRI of wrist and hand masses.

Unusual Case of Carpometacarpal Dislocation of All the Four Fingers of Ulnar Side of Hand.

Ferrofluid-associated Cutaneous Dyschromia: Discoloration of Hand and Fingers Following Accidental Exposure to Ferromagnetic Fluid.

Functional outcome of flexor tendon repair of the hand at Zone 5 and post operative early mobilization of the fingers.

Modeling of the biodynamic responses distributed at the fingers and palm of the hand in three orthogonal directions.

An MRI-compatible hand sensory vibrotactile system.

Subcutaneous release of trigger thumb and fingers in 210 fingers.

Subcutaneous release of trigger thumb and fingers in 210 fingers.

Arterial system of the fingers.

Open-source, low-cost, compliant, modular, underactuated fingers: towards affordable prostheses for partial hand amputations.

Tomosynthesis of the wrist and hand in patients with rheumatoid arthritis: comparison with radiography and MRI.

Mucous cysts of the fingers.

Iterative development and reliability of the OMERACT hand osteoarthritis MRI scoring system.

The triumph of fingers: mechanical hemostasis for postpolypectomy bleeding using the fingers.

Development of crossed and uncrossed tactile localization on the fingers.

Digital thermography of the fingers and toes in Raynaud's phenomenon.

Delineation of extensor tendon of the hand by MRI: usefulness of "soap-bubble" mip processing technique.

Serositis and desquamation of fingers and toes.

Percutaneous release of trigger fingers.

Multiple Fingers - One Gestalt.

Cellular fingers take hold.