(Radiographics. 2002;22:237-256.)
© RSNA, 2002
MR Imaging of Ligament and Tendon Injuries of the Fingers1
Juan A. Clavero, MD,
Xavier Alomar, MD,
Josep M. Monill, MD,
Mireia Esplugas, MD,
Pau Golanó, MD,
Manuel Mendoza, MD and
Antonio Salvador, MD
1 From the Department of Radiology, Diagnosis Médica, Calle Corcega 345, 08037 Barcelona, Spain (J.A.C., X.A., J.M.M., A.S.); the Department of Orthopedic and Traumatologic Surgery, Clínica FREMAP, Barcelona (M.E., M.M.); and the Department of Human Anatomy, University of Barcelona School of Medicine (P.G.). Presented as an education exhibit at the 2000 RSNA scientific assembly. Received March 19, 2001; revision requested July 3 and received August 8; accepted September 6. Address correspondence to J.A.C. (e-mail: as-md@ctv.es).
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Abstract
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Magnetic resonance (MR) imaging can provide important information for diagnosis and evaluation of soft-tissue trauma in the fingers. An optimal imaging technique should include proper positioning, dedicated surface coils, and specific protocols for the suspected abnormalities. Familiarity with the fine anatomy of the normal finger is crucial for identifying pathologic entities. MR imaging is a powerful method for evaluating acute and chronic lesions of the stabilizing articular elements (volar plate and collateral ligaments) of the fingers and thumbs, particularly in the frequently affected proximal interphalangeal and metacarpophalangeal joints. As in other body regions, MR imaging is also useful for depicting traumatic conditions of the extensor and flexor tendons, including injuries to the pulley system. In general, normal ligaments and tendons have low signal intensity on MR images, whereas disruption manifests as increased signal intensity. Radiologists need to understand the full spectrum of finger abnormalities and associated MR imaging findings.
© RSNA, 2002
Index Terms: Fingers and toes, 43.92 • Fingers and toes, injuries, 43.489 • Fingers and toes, MR, 43.1214 • Hand, injuries, 43.489 • Joints, injuries, 437.489 • Ligaments, injuries, 43.489 • Tendons, injuries, 43.489
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LEARNING OBJECTIVES FOR TEST 1
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After reading this article and taking the test, the reader will be able to:
- Describe the ligamentous and tendinous anatomy of the fingers at MR imaging.
- List the most common ligament and tendon injuries of the fingers.
- Recognize the MR imaging features of these lesions and discuss the role of MR imaging in their evaluation.
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Introduction
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Finger injuries are one of the most common traumatic injuries in both sports and work activities (1,2). Magnetic resonance (MR) imaging has fine soft-tissue contrast resolution and multiplanar capability and is thus very useful in diagnosing these lesions.
MR imaging allows optimal assessment of the condition of tendons (3–7), thus making it possible to evaluate the presence of a tear, the number of affected tendons, the extent of tendon retraction, and the presence of associated lesions. This information is used to determine the correct surgical plan and surgical approach and is especially useful for closed fractures. MR imaging is also very useful for diagnosis of a Stener lesion after tearing of the ulnar collateral ligament (UCL) of the thumb (8–10) and diagnosis of injuries of the pulley system (11,12). In addition, MR imaging may be used to assess lesions of the capsule and ligament in diagnosis of traumatic lesions involving the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints (13), especially in ambiguous or clinically equivocal cases or cases with negative results at plain radiography.
In this article, we review the normal anatomy of the finger together with the clinical and MR imaging findings of the most frequent soft-tissue injuries, which are divided into articular and tendon injuries. Articular injuries include volar plate and collateral ligament lesions of the PIP and MCP joints. Trauma to the extensor and flexor tendons can result in open or closed injuries. The most frequent of the latter are mallet finger deformity, boutonnière deformity, dislocation of the extensor tendon at the MCP joint, and avulsion of the flexor digitorum profundus tendon from the distal phalanx. Injuries of the pulley system are also described.
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MR Imaging
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Recently, several investigators have reported that MR imaging is an accurate method for evaluation of the anatomy and pathologic conditions of the finger. Hergan et al (9) reported a sensitivity and specificity of 100% for assessment of thumb UCL lesions in 17 patients, whereas Spaeth et al (10) reported a sensitivity of 100% and specificity of 94% for detection of displaced UCL fractures in 16 cadaveric specimens. Rubin et al (5) assessed tendinous pathologic conditions and reported a sensitivity of 92% and specificity of 100% for diagnosis of 12 high-grade flexor tendon tears in cadavers. Drapé et al (6) reported a sensitivity and specificity of 100% for diagnosis of frank tendinous ruptures after flexor tendon repair and a sensitivity of 91% and specificity of 100% for diagnosis of peritendinous adhesions in 63 injured fingers. More recently, Hauger et al (12) performed a study in cadavers and demonstrated direct identification of A2 (proximal phalanx) and A4 (middle phalanx) pulleys in 12 of 12 cases (100%) and direct diagnosis of an abnormal pulley in 100% (A2) and 91% (A3) of 33 cases. The extensor system has not been reviewed or assessed as extensively as the flexor system. However, Drapé et al (7) reported a sensitivity of 89%–92% for T2-weighted MR imaging in evaluation of normal sagittal bands in the extensor hood.
MR imaging was performed on a 0.35-T open system (Opart; Toshiba America MRI, San Francisco, Calif). A dedicated coil for studying small parts of the limbs was used to enhance spatial resolution (flexible small parts coil for Opart; Toshiba America MRI). The open system allowed comfortable supine positioning of the patient, with the arm at the side of the body, thus reducing motion artifacts and placing the hand within the magnetic field. Routine MR imaging of the finger was performed in the axial, sagittal, and coronal planes in relation to the MCP and PIP joints of the extended finger. In some cases, sagittal images were obtained with flexion of the affected finger.
T1-weighted images (repetition time msec/echo time msec = 450/15), T2*-weighted gradient-echo images (600/34, 25° flip angle), and short inversion time inversion-recovery images (1,900/40, 95-msec inversion time) were obtained with an 8–9-cm field of view, a 256/320 x 192/256 acquisition matrix, two to three signals acquired, and a section thickness of 3–4 mm with no gap. In addition, 1–2-mm-thick sections were obtained with a three-dimensional T1-weighted gradient-echo pulse sequence (35/5, 70° flip angle).
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PIP Joint
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Anatomy
The PIP joint is a hinged joint with a bicondylar anatomy that allows a wide range of flexion and extension movements (14). The main stabilizers of the joint are the surrounding soft tissues, especially the collateral ligaments and the volar plate (Fig 1) (15). The extensor mechanism, flexor tendons, and retinacular ligaments play a major role in dynamic stability. The collateral ligament complex consists of the collateral ligament proper and an accessory collateral ligament. The former begins at the dorsolateral aspect of the head of the proximal phalanx and inserts at the volar and lateral aspects of the base of the middle phalanx. The latter starts from the same area but inserts at the volar plate. The proper collateral ligament is taut in flexion, whereas the accessory collateral ligament is taut in extension. The volar plate is a thick fibrocartilaginous structure that constitutes the palmar aspect of the PIP joint capsule. Distally, it is firmly attached to the volar lip of the base of the middle phalanx. Proximally, the attachment of the volar plate to the proximal phalanx is more elastic and is U-shaped due to two lateral bands, which are called the "checkrein" ligaments. The volar plate prevents hyperextension of the PIP joint (15). Dorsally, the PIP joint is stabilized by the dorsal extensor apparatus, which consists of a central slip that inserts on the dorsal tubercle of the middle phalanx and lateral slips that are connected by retinacular ligaments.
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Figure 1. Anatomy of the PIP joint. Drawing (lateral view) shows the accessory collateral ligament (ACL), extensor central slip (ECS), flexor tendons (FT), middle phalanx (MP), proper collateral ligament (PCL), proximal phalanx (PP), and volar plate (VP).
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On MR images, normal collateral ligaments appear as sharply defined low-signal-intensity bands extending from the proximal phalanx to the middle phalanx (Fig 2). They are best visualized in the coronal projection. The volar plate is a low-signal-intensity structure that is best seen in a sagittal plane (Fig 3).
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Figure 2a. Collateral ligaments of the PIP joint. MP = middle phalanx, PP = proximal phalanx. (a) Coronal T1-weighted MR image shows the collateral ligaments (arrows). (b) Photograph of a coronal cross section of a cadaveric finger shows the collateral ligaments (arrows).
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Figure 2b. Collateral ligaments of the PIP joint. MP = middle phalanx, PP = proximal phalanx. (a) Coronal T1-weighted MR image shows the collateral ligaments (arrows). (b) Photograph of a coronal cross section of a cadaveric finger shows the collateral ligaments (arrows).
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Figure 3a. Volar plate of the PIP joint. MP = middle phalanx, PP = proximal phalanx. (a) Sagittal T1-weighted MR image shows the volar plate (arrow). (b) Photograph of a sagittal cross section of a cadaveric finger shows the volar plate (arrow).
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Figure 3b. Volar plate of the PIP joint. MP = middle phalanx, PP = proximal phalanx. (a) Sagittal T1-weighted MR image shows the volar plate (arrow). (b) Photograph of a sagittal cross section of a cadaveric finger shows the volar plate (arrow).
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Injuries
The PIP joint is the most commonly injured joint in the hand, and its range of motion usually decreases after injury. From a clinical point of view, we classified PIP joint injuries in terms of instability in the coronal plane and instability in the sagittal plane.
Instability in the Coronal Plane.—
When an abducting or adducting force is applied to the PIP joint while the finger is extended, three main injuries may occur: a ligamentous sprain with no loss of articular stability, a partial ligamentous tear with laterolateral articular instability, and a complete ligamentous rupture with major instability and articular luxation. The latter is usually associated with total or partial avulsion of the volar plate from the base of the middle phalanx. Treatment, which may be conservative or surgical, is still a matter of controversy (16,17). MR imaging criteria for diagnosis of acute collateral ligament tears include discontinuity, detachment, or thickening of the ligament together with increased intraligamentous signal intensity on T2-weighted images, which is indicative of edema or hemorrhage (Fig 4). Obliteration of the fat planes around the ligament and extravasation of joint fluid into the adjacent soft tissues may also be observed. Chronic tears often demonstrate thickening of the ligament, which is probably secondary to scar formation. Thinning, elongation, or a wavy contour of the ligament may also be seen.
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Figure 4a. Tear of the collateral ligament of the PIP joint. Coronal (a) and axial (b) T2-weighted MR images show a complete proximal tear of the radial collateral ligament (arrows). The tear appears as a complete interruption of the ligamentous fibers with intra- and periligamentous high signal intensity secondary to edema, hemorrhage, and probable extravasation of intraarticular fluid.
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Figure 4b. Tear of the collateral ligament of the PIP joint. Coronal (a) and axial (b) T2-weighted MR images show a complete proximal tear of the radial collateral ligament (arrows). The tear appears as a complete interruption of the ligamentous fibers with intra- and periligamentous high signal intensity secondary to edema, hemorrhage, and probable extravasation of intraarticular fluid.
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Instability in the Sagittal Plane.—
Instability in the sagittal plane is caused by hyperextension of the PIP joint or rotational longitudinal compression.
Lesions caused by hyperextension are the lesions most frequently seen in sports practice and are sometimes associated with major articular instability. These lesions include different degrees of dorsal articular displacement, which are divided into three types according to the degree of articular instability (type III is a fracture-dislocation of the base of the middle phalanx) (15,17).
In type I lesions, hyperextension results in avulsion of the volar plate from the base of the middle phalanx or, less frequently, from the proximal insertion point of the checkrein ligaments on the proximal phalanx. With no treatment, the natural evolution of distal disruption of the volar plate from the middle phalanx is hyperextension of the PIP joint, which causes a swanneck deformity due to articular injury (2). Conversely, the natural evolution of proximal disruption of the volar plate from the proximal phalanx causes a flexion deformity of the PIP joint, the so-called pseudoboutonnière deformity (16), with an intact extensor mechanism. MR imaging findings of injury to the volar plate include nonhomogeneous signal intensity on T1- and T2-weighted images, together with thickening and contour irregularities. Disrupted attachment with a gap is observed when avulsion of the volar plate takes place (Fig 5).
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Figure 5. Type I hyperextension lesion of the PIP joint. Sagittal T1-weighted MR image shows distal avulsion of the volar plate from the base of the middle phalanx and proximal displacement (arrows).
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In type II lesions, involvement of the periarticular soft tissues is more extensive, with volar plate avulsion and a major split between the components of the collateral ligament complex. The joint shows a higher loss of stability than in type I lesions, as dorsal subluxation or even luxation of the middle phalanx may take place due to traction by the extensor apparatus.
Type III lesions are characterized by a fracture-dislocation of the volar base of the middle phalanx. These lesions may be classified according to the size of the fragment and the resultant stability of the joint (14). A stable injury usually involves less than 40% of the articular surface while leaving the collateral ligaments attached to the middle phalanx. An unstable injury involves more than 40% of the articular surface with the volar plate and collateral ligaments attached to the volar fragment, thus inducing a tendency toward dorsal luxation (Fig 6).
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Figure 6a. Type III hyperextension lesion (unstable fracture-dislocation) of the PIP joint. Sagittal T1-weighted (a) and short inversion time inversion-recovery (b) MR images show a fracture (solid arrow) that involves more than 40% of the articular arch of the middle phalanx with dorsal displacement of the middle phalanx. Note the normal volar plate (open arrow) attached to the bone fragment.
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Figure 6b. Type III hyperextension lesion (unstable fracture-dislocation) of the PIP joint. Sagittal T1-weighted (a) and short inversion time inversion-recovery (b) MR images show a fracture (solid arrow) that involves more than 40% of the articular arch of the middle phalanx with dorsal displacement of the middle phalanx. Note the normal volar plate (open arrow) attached to the bone fragment.
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The treatment is conservative in all cases except for unstable type III injury (fracture-dislocation), which needs open reduction and internal fixation.
The mechanism of lesions due to compression is rotational longitudinal compression of a semi-flexed PIP joint, which causes volar luxation or subluxation of the middle phalanx with unilateral disruption of the collateral ligament and at least partial avulsion of the volar plate (17). These infrequent lesions are severe due to the possible presence of an associated lesion of the extensor apparatus (Fig 7). If an additional rotational force is applied together with the longitudinal compression, one of the condyles of the proximal phalanx might become trapped in a "buttonhole" fashion between the central slip and the lateral band. Open surgical reduction is mandatory in these cases. The central slip may sometimes be avulsed. If left untreated, this injury results in chronic boutonnière deformity: flexion of the PIP joint and extension of the distal interphalangeal (DIP) joint (18).
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Figure 7. Volar dislocation of the PIP joint. Sagittal T1-weighted MR image shows a tear of the volar plate (thick arrow), which manifests as high signal intensity and contour irregularity. There is also a partial tear of the extensor central slip at its insertion on the base of the middle phalanx (thin arrow).
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MCP Joint
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Anatomy
Although the supporting structures of the MCP joint and PIP joint are similar, the bony anatomy of the unicondylar MCP joint allows significant radial and ulnar deviation and some rotation. The collateral ligaments of the MCP joint are taut in flexion and lax in extension, allowing abduction and adduction (13). The volar plate is an important stabilizer of this joint and is interconnected with the adjacent MCP joints by the deep transverse metacarpal (interglenoid) ligament. The extensor hood (particularly its sagittal bands), which stabilizes the extensor tendon at this level, also contributes to the stability of the joint (Figs 8, 9) (19).
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Figure 8a. Anatomy of the MCP joint. Lateral (a) and axial (b) drawings show the accessory collateral ligament (ACL), deep transverse metacarpal ligament (DTML), extensor digitorum communis tendon (EDC), flexor tendons (FT), interosseous tendons (IT), lumbrical tendon (LT), metacarpal (MC), proper collateral ligament (PCL), proximal phalanx (PP), A1 pulley (PS), sagittal bands (SB), and volar plate (VP).
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Figure 8b. Anatomy of the MCP joint. Lateral (a) and axial (b) drawings show the accessory collateral ligament (ACL), deep transverse metacarpal ligament (DTML), extensor digitorum communis tendon (EDC), flexor tendons (FT), interosseous tendons (IT), lumbrical tendon (LT), metacarpal (MC), proper collateral ligament (PCL), proximal phalanx (PP), A1 pulley (PS), sagittal bands (SB), and volar plate (VP).
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Figure 9a. Anatomy of the MCP joint. (9a) Sagittal T2-weighted MR image shows the volar plate (arrow). MC = metacarpal, PP = proximal phalanx. (9b, 9c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric hand (c) show the volar plate (*), deep transverse metacarpal ligament (large solid arrows), collateral ligaments (arrowheads), sagittal bands (small solid arrows), and extensor tendon (open arrow).
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Figure 9b. Anatomy of the MCP joint. (9a) Sagittal T2-weighted MR image shows the volar plate (arrow). MC = metacarpal, PP = proximal phalanx. (9b, 9c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric hand (c) show the volar plate (*), deep transverse metacarpal ligament (large solid arrows), collateral ligaments (arrowheads), sagittal bands (small solid arrows), and extensor tendon (open arrow).
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Figure 9c. Anatomy of the MCP joint. (9a) Sagittal T2-weighted MR image shows the volar plate (arrow). MC = metacarpal, PP = proximal phalanx. (9b, 9c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric hand (c) show the volar plate (*), deep transverse metacarpal ligament (large solid arrows), collateral ligaments (arrowheads), sagittal bands (small solid arrows), and extensor tendon (open arrow).
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Injuries
Dislocation of the MCP joint is uncommon, but when it occurs it is usually dorsalward and follows the forced hyperextension of the finger. MCP dislocations may be simple or complex. In simple dislocations, the volar plate is not interposed in the joint and the treatment is conservative. Complex MCP dislocations may not be reduced due to the interposition of the volar plate (16). Open surgical reduction is necessary. MR imaging may be used to show the state of the volar plate and allows exact identification of its location and displacement (Fig 10). One collateral ligament may be ruptured after the dislocation and secondarily to the lateral deviation, with the MCP joint in a flexion position (16). Intraarticular interposition of the ligament is also possible (Fig 11).
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Figure 10. Simple dislocation of the MCP joint. Sagittal T1-weighted MR image shows distal avulsion of the volar plate of the MCP joint (solid arrow). Note the normal volar plate at the PIP joint (open arrow).
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Figure 11a. Complete tear of the radial collateral ligament of the MCP joint with intraarticular interposition of the ligament. (a) Coronal T2-weighted MR image shows proximal complete disruption and retraction of the radial collateral ligament (arrows). (b) Sagittal T2-weighted MR image shows the collateral ligament (arrow) interposed between the volar plate (arrowhead) and the MCP joint. Note the volar subluxation of the proximal phalanx.
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Figure 11b. Complete tear of the radial collateral ligament of the MCP joint with intraarticular interposition of the ligament. (a) Coronal T2-weighted MR image shows proximal complete disruption and retraction of the radial collateral ligament (arrows). (b) Sagittal T2-weighted MR image shows the collateral ligament (arrow) interposed between the volar plate (arrowhead) and the MCP joint. Note the volar subluxation of the proximal phalanx.
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Anatomy of the MCP Joint of the Thumb
The MCP joint of the thumb is a condylar-type articulation that allows motion primarily in the flexion-extension axis and also some degree of rotation. Similarly to the PIP and MCP joints of the finger, the MCP joint of the thumb is stabilized by the volar plate, collateral ligaments, and musculotendinous structures. The adductor pollicis has a strong tendinous point of insertion into the proximal phalanx and volar plate–sesamoid complex. Some of its fibers also contribute to the adductor aponeurosis, which covers the UCL (Fig 12) (20).
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Figure 12. Normal anatomy of the UCL. Oblique coronal T2-weighted MR image shows the UCL (arrow) and overlying adductor aponeurosis (arrowhead). MC = metacarpal, PP = proximal phalanx.
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Gamekeeper Thumb
Injuries to the UCL of the first MCP joint are frequent. This injury is very commonly caused by skiing accidents and is also called "skier’s thumb." It occurs after violent hyperabduction of the thumb. Rupture of the UCL may be total or partial and usually takes place at its distal point of insertion. It might be accompanied by bone avulsion. In total rupture of the UCL, retraction may be mild (with the torn UCL beneath the adductor aponeurosis) or severe and associated with interposition of the adductor aponeurosis (with the torn UCL lying superficially at the proximal end of the aponeurosis). The latter condition, which is called a Stener lesion (21), requires surgical treatment because conservative treatment would lead to chronic instability. Usually, the difference between a complete and an incomplete tear can be discerned after physical examination. A complete tear induces the appearance of a palpable mass in the ulnar aspect of the joint and instability to radial stress reaching an angle of 30° or higher when compared with the contralateral thumb (20). Nevertheless, the difference between a nondisplaced UCL tear and a Stener lesion is not unequivocal at clinical examination (8). Moreover, the maneuvers during the clinical examination may turn a nondisplaced lesion into a displaced one.
MR imaging is a sensitive technique for studying the Stener lesion (8–10,22). A nondisplaced torn UCL appears on MR images as a gap in the otherwise normally located UCL (Fig 13). The ligament usually appears to be thickened beneath the adductor aponeurosis. A displaced rupture is diagnosed when the torn UCL is displaced to the proximal margin of the adductor aponeurosis (Fig 14). The ligament usually appears as a rounded or stumplike area of low signal intensity located more superficially than a normal ligament. In the Stener lesion, the adductor aponeurosis, which normally appears as a thin hypointense structure, usually shows surrounding hyperintense effusion on T2-weighted MR images.
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Figure 13. Nondisplaced tear of the UCL. Oblique coronal T1-weighted MR image shows discontinuity of the distal portion of the UCL (arrow), which lies beneath the adductor aponeurosis.
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Figure 14. Ruptured UCL with a Stener lesion. Oblique coronal T2-weighted MR image shows a torn UCL (straight arrow), which is retracted and lies superficial to the adductor aponeurosis (curved arrow).
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Extensor Tendons
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Anatomy
Digit extension involves simultaneous action of both extrinsic and intrinsic extensor muscles. Extrinsic muscles originate in the forearm and elbow and insert in the hand. These tendons are the extensor digitorum communis, extensor indicis proprius (EIP), and extensor digiti quinti minimi (EDQM). Their function is primarily extension of the MCP joint but also extension of the PIP and DIP joints (23). The EIP and EDQM tendons move independently, allowing extension of the index and small fingers through a considerable range of movements. The intrinsic muscles are the interosseous and lumbrical muscles, which originate and insert in the hand. Their function is extension of the PIP and DIP joints and flexion of the MCP joint (24).
The extensor tendons reach the hand by passing through fibro-osseous tunnels or dorsal compartments in the wrist. Near the midportion of the metacarpals, the extensor tendons are interconnected by the juncturae tendinum, which prevent independent extension of the digits (23,25). At the MCP joint, these extrinsic tendons are stabilized over the dorsum of the metacarpal head by the extensor hood (Figs 8, 15, 16). The sagittal bands are the main component of the extensor hood, which starts mainly at the volar plate and has a dorsal tendinous point of insertion, gliding with the extensor system as the digit moves. Distal to the sagittal bands, the transverse fibers of the intrinsic tendons contribute to the anatomy of the extensor hood. Distal to the MCP joint, the extrinsic and intrinsic tendons blend into the dorsal apparatus and are circumferentially distributed over the dorsum of the fingers. The extrinsic extensor tendon continues in the central and lateral slips (26) or bands (27). The central slip inserts on the base of the middle phalanx. The intrinsic tendons contribute to form the lateral slips. Moreover, they send fibers medially to form part of the central slip. Once the lateral slips receive the contribution of the intrinsic muscles, they are called conjoint tendons and converge distally to form the terminal tendon, which inserts on the base of the distal phalanx (25). Between the conjoint tendons, the triangular ligament keeps these structures in a position that is dorsal to the rotational axis of the PIP joint. The tendons of the dorsal apparatus are also spatially and functionally connected by retinacular ligaments at the PIP joint and middle phalanx.
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Figure 15a. Anatomy of the extensor apparatus. Drawing (dorsal view) (a) and photograph of a transilluminated anatomic specimen of the extensor apparatus of the index finger (b) show the central slip (CS), conjoint tendon (CT), extensor digitorum communis tendon (EDC), intrinsic muscles (IM), lateral slip (LS), retinacular ligaments (RL), sagittal bands (SB), transverse fibers (TF), triangular ligament (TL), and terminal tendon (TT).
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Figure 15b. Anatomy of the extensor apparatus. Drawing (dorsal view) (a) and photograph of a transilluminated anatomic specimen of the extensor apparatus of the index finger (b) show the central slip (CS), conjoint tendon (CT), extensor digitorum communis tendon (EDC), intrinsic muscles (IM), lateral slip (LS), retinacular ligaments (RL), sagittal bands (SB), transverse fibers (TF), triangular ligament (TL), and terminal tendon (TT).
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Figure 16a. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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Figure 16b. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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Figure 16c. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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Figure 16d. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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Figure 16e. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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Figure 16f. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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Figure 16g. (16a) Sagittal T1-weighted MR image shows the insertion of the central slip on the base of the middle phalanx (solid arrow) and the insertion of the terminal tendon on the base of the distal phalanx (open arrow). (16b, 16c) Axial T1-weighted MR image (b) and photograph of an axial cross section of a cadaveric finger (c) obtained at the MCP joint show the extensor digitorum communis tendon (open arrow), sagittal bands (arrowheads), interosseous tendon (straight solid arrow), and lumbrical tendon (curved arrow). (16d, 16e) Axial T1-weighted MR image (d) and photograph of an axial cross section of a cadaveric finger (e) obtained proximal to the PIP joint show the central slip (open arrow) and lateral slips (solid arrows). (16f, 16g) Axial T1-weighted MR image (f) and photograph of an axial cross section of a cadaveric finger (g) obtained at the middle phalanx show the conjoint tendons (arrowheads in f, arrows in g).
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On MR images, the normal extensor tendons appear as thin structures of very low signal intensity in the expected locations (Fig 16). The axial and sagittal planes are the most useful for tendon identification. Stabilizing fibrous structures, especially the sagittal bands, are characterized by uniform low signal intensity, as is the case with other ligamentous or retinacular structures. These bands are best seen in axial planes.
Injuries
Injuries to the extensor mechanism of the finger are common because it consists of thin, superficially located structures. These anatomic structures predispose tendons to lacerations and also to closed tendon injuries, including avulsion.
Open Injuries.—
Owing to characteristic anatomic features of the extensor tendon system and to the specific findings according to its lesional topography, the concept of anatomic zones has been developed. Various classifications have been developed; the most accepted one includes eight zones (28), with zone 1 located at the DIP joint and zone 8 at the distal forearm. The odd zones correspond to the articular areas, where the extensor apparatus contains longitudinal fibers and transverse elements that maintain the apparatus in a centered position and attached to the joint. Therefore, an injury to these zones may create a lesion of the extensor apparatus and the articular structures (29). Laceration of the terminal tendon may take place in zone 1, leading to deformity of the distal phalanx in flexion (open mallet deformity) (Fig 17). Laceration of the central slip is possible in zone 3 (Fig 18), with eventual development of a boutonnière deformity secondary to flexion of the PIP joint and hyperextension of the DIP joint. In zone 5, besides lesions of the extensor digitorum communis tendon, there may be injury to the sagittal bands, which may lead to tendinous subluxation or dislocation. In the even zones, owing to the semicircular morphology of the extensor apparatus that covers the dorsal aspect of the fingers, a partial lesion is usually found (as a single wound seldom provokes a complete lesion). In total laceration, the extensor apparatus does not usually show significant retraction due to its attachment system and its connections (29,30). The extensive vascularization of the extensor apparatus predisposes to formation of adhesions from the injured tendon to adjacent tissues, such as bone or the underlying joint. These adhesions may induce important functional impairment and deformities (30). The treatment of choice is tendinous surgical suturing (27).
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Figure 17. Complete laceration of the conjoint tendon at its distal insertion on the base of the distal phalanx. Sagittal T1-weighted MR image shows disruption of the conjoint tendon (arrows) with soft-tissue edema and hemorrhage. Flexion deformity of the distal phalanx is apparent. Note the metallic artifacts secondary to a wound.
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Figure 18a. Complete laceration of the central slip at its insertion on the base of the middle phalanx. Sagittal (a) and axial (b) T2-weighted MR images show disruption of the central slip with a hyperintense gap (arrows). This acute case was secondary to a wound. Note the absence of the classic boutonnière deformity.
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Figure 18b. Complete laceration of the central slip at its insertion on the base of the middle phalanx. Sagittal (a) and axial (b) T2-weighted MR images show disruption of the central slip with a hyperintense gap (arrows). This acute case was secondary to a wound. Note the absence of the classic boutonnière deformity.
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Diagnosis of a partial-thickness tear of the extensor apparatus with MR imaging is based on the presence of areas of increased signal intensity on T1-weighted (and sometimes T2-weighted) images, located within a portion of the tendon. These areas do not extend to all of the tendon. A complete tendon laceration appears as an area of discontinuity with fraying and irregularities at both ends of the ruptured tendon (Figs 17, 18). MR imaging can also depict the gap produced by the lesion, even if its extension is limited. When the laceration is acute, the tendon gap has intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images; these findings are consistent with edema and hemorrhage. MR imaging may show the presence of adhesions as an area of blurring at the margins of the tendinous surface in association with abnormal signal intensity in the surrounding fat, together with distortion of the normal anatomy of the tendon (Fig 19).
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Figure 19. Adhesions of the extensor system. Axial T1-weighted MR image obtained just proximal to the PIP joint shows hypointense scar tissue (solid arrow) beside an asymmetrically swollen and volarly displaced lateral slip (open arrow), which includes adhesions secondary to a previous wound.
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When these open wounds are due to injury caused by metallic devices, a frequent finding is the presence of microartifacts, which appear as tiny areas of signal void (Fig 17). As in other anatomic regions, a possible "magic angle" effect can be detected when the orientation of the extensor tendons approaches an angle of 55° in relation to the direction of the B0 magnetic field, resulting in increased intratendinous signal intensity, which may mimic pathologic changes (31).
Closed Injuries.—
Closed tendon injuries include mallet finger, boutonnière deformity, and subluxation or dislocation of the extensor tendon mechanism at the MCP joint.
A mallet finger injury results from a lesion of the bony or ligamentous attachment of the extensor mechanism to the distal phalanx. This loss of extensor continuity results in incomplete extension of the DIP joint or extensor lag. This is the most common closed tendon injury seen in sports (32). It usually occurs when the tip of the finger is struck by or against an object, resulting in acute flexion of the DIP joint (30). Mallet finger can also result from a direct blow to the dorsum of the distal DIP joint or be secondary to a hyperextension force applied at this joint (18). At clinical examination, the patient has pain and swelling at the dorsum of the DIP joint and cannot extend the joint. Presently, the treatment most commonly used is closed splinting with the DIP joint in extension (30,33). If left untreated, a mallet deformity will frequently progress to a swan-neck deformity (18). This is the result of a flexion deformity of the DIP joint together with hyperextension of the PIP joint, which is caused by retraction of the extensor mechanism.
Injuries of the terminal extensor tendon may be detected on sagittal MR images, which allow confirmation of the diagnosis in cases with no bone avulsion. The MR imaging appearance overlaps that of open mallet injuries (Fig 17).
A boutonnière deformity is the result of an injury to the central slip at or near its point of insertion on the base of the middle phalanx. Less frequently, a boutonnière deformity is associated with a fracture of the central slip attachment. Rupture of the central slip and eventual boutonnière deformity may be caused by a blow to the dorsum of the middle phalanx, acute violent flexion of the PIP joint, or volar dislocation of the PIP joint (18,30). In the early acute phase, the results of physical examination may be misleading because the lateral bands may still be in their proper anatomic position and still extend the PIP joint. Initial findings include pain and swelling of the PIP joint, a mild extension lag, and reduced extension strength against resistance. If the injury goes unrecognized, the lateral bands move volarly to the axis of rotation of the PIP joint. This induces flexion of the PIP joint and an increase in the force on the intact terminal extensor insertion, with subsequent extension of the DIP joint (34). The head of the proximal phalanx can be displaced through the defect at the level of the extensor apparatus. The deformity is not apparent during the first 7–14 days (30). Extension splinting of the PIP joint is the treatment of choice for acute boutonnière deformity. Surgical intervention is required when soft-tissue interposition prevents congruent reduction after dislocation of the PIP joint or when a large displaced bone fragment is present. Surgical reconstruction is the treatment of choice for chronic symptomatic cases (34).
MR imaging is an effective method for detecting lesions of the central slip, especially during the acute phase, when the clinical diagnosis is not unequivocal. Axial and sagittal MR images depict complete tears of the central extensor tendon as a complete disruption of the tendon fibers (Fig 20). MR imaging can provide useful information about associated volar plate and ligamentous lesions of the PIP joint, as described elsewhere.
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Figure 20. Boutonnière deformity. Sagittal T1-weighted MR image shows discontinuity of the central slip at its distal insertion on the base of the middle phalanx (long arrow). A classic deformity with flexion of the PIP joint and extension of the DIP joint is seen (short arrows).
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Subluxation or dislocation of the extensor digitorum communis tendon at the MCP joint occurs as a result of tearing of the sagittal bands of the extensor hood. This injury is the result of a direct blow forcing the finger into flexion or of forced flexion and ulnar deviation of the finger (18). Ulnar subluxation is more common and usually affects the middle finger. Radial subluxation is unusual but can occur with forced valgus injury (7). At clinical examination, the patient has pain and swelling over the MCP joint. There is usually an inability to completely extend the MCP joint. In chronic untreated cases, the patient has a history of multiple episodes of pain and swelling over the MPC joint with a snapping sensation in the finger. If the injury is in its acute phase, conservative treatment with splinting of the MCP joint in extension is recommended (35). Surgical correction is necessary in chronic symptomatic cases (36).
MR imaging allows direct assessment of the position of the tendon relative to the metacarpal head. Dislocation is best depicted on axial images (Fig 21). MR imaging is also useful in evaluation of extensor hood injuries (7). In acute cases, the findings include morphologic and signal intensity abnormalities within and around the extensor hood components (particularly the sagittal bands) on axial T1- and T2-weighted images, together with poor definition, focal discontinuity, and focal thickening (Fig 22).
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Figure 21. Radial dislocation of the extensor digitorum communis tendon at the MCP joint. Consecutive axial T1-weighted MR images show radial subluxation of the extensor digitorum communis tendon (solid arrows) with a normal central position at the distal level (bottom right image). Note the lack of visualization or poor definition of the cubital sagittal band (open arrow), which suggests a chronic tear.
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Figure 22. Partial tear of the radial sagittal band of the middle finger. Axial T2-weighted MR image shows increased signal intensity and poor definition of the radial sagittal band (arrow) near the extensor digitorum communis tendon.
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Flexor Tendons
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Anatomy
The digital flexor tendons pass through the carpal tunnel before spreading out in the palm toward their respective fingers. Each finger has two flexor tendons: the flexor digitorum superficialis (FDS), which inserts on the midportion of the mid
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Abstract
LEARNING OBJECTIVES FOR TEST...
