Radiography

Imaging evaluation of the hand and fingers often begins with conventional radiographs, especially in the setting of acute trauma for suspected fracture or dislocation. Radiographs are usually adequate to delineate the specific osseous abnormality following trauma. Evaluation in other clinical settings such as suspected arthritis, infection, or mass usually begins with radiographs as well but often proceeds to more advanced imaging. Anteroposterior, lateral, and oblique radiographs of the hand are usually adequate in the setting of trauma to visualize fractures or malalignment. The reverse anteroposterior oblique view, sometimes referred to as the ball-catcher’s view, is helpful in demonstrating the early erosive disease seen in inflammatory arthritis. Anterolateral, lateral, and oblique views of the fingers and thumb are also usually adequate to demonstrate osseous abnormalities. If the suspected abnormality is isolated to a single digit, radiographs can be coned down to that particular digit. A good-quality lateral view of the finger is mandatory when evaluating for fracture. If multiple fingers are included in the same view, care must be taken to avoid overlap of the digits on the lateral view.

Computed Tomography

Computed tomography (CT) is rarely required in the evaluation of the hand and fingers, although it may occasionally be helpful in delineating the exact nature of complex fractures or in demonstrating the matrix of a lesion.

Ultrasound

Ultrasound may be particularly useful in the dynamic evaluation of tendon and pulley injuries of the hand and fingers and can be very useful in the localization of suspected foreign bodies within the soft tissues of the hand and fingers. Moreover, ultrasound can be useful in the evaluation of soft tissue masses such as ganglion and giant cell tumor of the tendon sheath. A thorough evaluation requires either an ultrasound technologist who is highly skilled in musculoskeletal imaging or a physician to direct or perform the imaging. A small parts transducer is mandatory for the evaluation of the small soft tissue structures of the digits, and comparison with the adjacent normal fingers can be very helpful.

Magnetic Resonance Imaging

Recent advances in MR technology such as improvement in coil technology and improved pulse sequences resulting in enhanced signal-to-noise ratios have made high-quality magnetic resonance imaging (MRI) of the small anatomic structures of the hand and fingers a reality. It is becoming common for the clinician to request MRI of the hand or even of an individual finger to evaluate for a specific soft tissue injury following acute trauma or to evaluate a palpable mass or a suspected infection. With improved treatment options for early arthritis, MRI is being used increasingly more frequently for the evaluation of early inflammatory arthropathies to detect subtle osseous changes such as marrow edema and tiny erosions that are not yet visible on conventional radiographs.

In the past, conventional radiography was the primary means available for imaging the hand and fingers in the setting of acute trauma, and evaluation was limited to the osseous structures or to indirect signs that would indicate a specific soft tissue injury. Now, however, MRI can accurately depict even the smallest of soft tissue structures of the hand and fingers. It has therefore become increasingly important for the radiologist to have a detailed understanding of the anatomy of the soft tissue structures and to have knowledge of the specific injury patterns that occur in the hand and fingers. When a soft tissue injury of a specific finger is suspected, inclusion of the two adjacent digits on MRI is helpful to allow comparison with the normal anatomy.

Metacarpophalangeal Joint

The metacarpophalangeal joints each have a strong fibrous capsule that is composed of two cord-like collateral ligaments and a thickened volar component referred to as the volar plate (Fig. 10-1A). The second through fifth metacarpal heads are also stabilized in the coronal plane by deep transverse metacarpal ligaments. These ligaments extend along the volar aspect of the metacarpophalangeal joints connecting the volar plates of adjacent metacarpophalangeal joints and have also been referred to as the “intervolar plate ligaments.” The dorsal aspect of the joint is stabilized primarily by the extensor “hood” and the extensor tendon. This complex capsular anatomy provides tremendous stability at the level of the second through fifth metacarpophalangeal joints, and, as a result, complete dislocation at this level is uncommon.

Figure 10-1 Metacarpophalangeal joint capsule. A, The normal capsule is composed of two cordlike collateral ligaments that are best demonstrated on T2-weighted coronal images. B, Coronal T2-weighted image of the fifth metacarpophalangeal joint demonstrates complete disruption of the proximal aspect of the radial collateral ligament and a high-grade partial-thickness tear of the ulnar collateral ligament. There is marked thickening of more distal fibers of the radial collateral ligament, and there is extensive adjacent soft tissue edema and a bone contusion involving the base of the proximal phalanx.

Although full-blown medial or lateral dislocation of the metacarpophalangeal joint only rarely occurs, valgus or varus stress injuries can result in a sprain or disruption of the collateral ligaments. Injuries to the collateral ligaments are described either as a sprain (thickening of the collateral ligament with adjacent soft tissue edema) or as a partial- or full-thickness disruption (Fig. 10-1B). Acute injuries show extensive pericapsular soft tissue edema, whereas chronic injuries demonstrate thickening but lack the associated soft tissue edema. Bone contusions are often seen accompanying capsular injuries and usually result from the impaction of two bones at the time of injury. They may indicate subluxation or dislocation at the time of injury. Contusions may be accompanied by small cortical avulsion fractures, which occur at the level of attachment of the collateral ligament. Bone contusions are best depicted on fat-suppressed T2-weighted images, whereas avulsion fractures are best seen on T1-weighted images without fat saturation or gradient-echo images and may require evaluation with radiographs for detection.

Volar plate injury can result from a significant hyperextension injury or from either a dorsal or volar dislocation of the metacarpophalangeal joint. After reduction, MRI can accurately delineate the status of the volar plate, which usually remains intact at its distal attachment site, with most injuries occurring near the proximal attachment site (Fig. 10-2). Injuries range from a mild sprain to complete disruption or avulsion, and the volar plate may become entrapped within the metacarpophalangeal joint, resulting in an incomplete reduction or preventing full range of motion after reduction. Volar plate injuries are described as either a partial or complete disruption. Intra-articular entrapment of a portion of the volar plate should also be noted. Volar plate injuries of the metacarpophalangeal joint are often accompanied by a fracture of the volar aspect involving the articular surface at the base of the proximal phalanx, which typically occurs at the time of dorsal dislocation. The size of the fragment and the congruence of the articular surface should be described. A fracture that involves more than 50% of the articular surface or demonstrates significant articular surface step-off usually requires open reduction and fixation.

Figure 10-2 Volar plate injury of metacarpophalangeal joint. A, Sagittal T2-weighted image shows complete avulsion of the proximal fibers of the volar plate from its normal attachment site on the metacarpal neck. B, Axial T2-weighted images are often helpful because they demonstrate soft tissue edema located along the volar aspect of the involved joint.

MR evaluation of the collateral ligaments is best performed in the coronal and axial imaging planes, whereas volar plate injuries are best detected on sagittal and axial images. A T2-weighted sequence with fat saturation or an STIR (short tau inversion recovery) sequence can aid in the detection of soft tissue edema, which often accompanies an acute injury. Use of a three-dimensional gradient-echo sequence allows visualization of these very small soft tissue structures, whereas T1-weighted images are very helpful in the evaluation of associated osseous abnormalities and in particular small avulsion fractures that often accompany volar plate and collateral ligament injuries.

Interphalangeal Joint

The capsular anatomy of the interphalangeal joint is very similar to that of the metacarpophalangeal joint. There is a strong fibrous capsule that is composed of medial and lateral collateral ligaments and a strong thickened volar component referred to as the volar plate (Figs. 10-3 and 10-4). The extensor apparatus including the extensor tendon and its numerous attachments provides the major support along the dorsal aspect of the interphalangeal joint.

Figure 10-3 Normal anatomy of the volar plate shown in the lateral projection. The distal aspect of the volar plate is thick and attaches tightly to the base of the more distal phalanx while thin periscoping ligamentous-like attachments extend approximately 1 cm proximal to the interphalangeal joint.

Figure 10-4 Normal capsular anatomy of the interphalangeal joints. A, Sagittal T2-weighted image shows the volar plate, a thickening of the capsule along the volar aspect of the joint that sits deep to the flexor tendon. The distal aspect of the volar plate is thick and attaches tightly to the base of the distal phalanx. The volar plate has thin periscoping ligamentous-like attachments approximately 1 cm proximal to the joint. A distal recess is present, which compresses in flexion. This recess combined with cartilage undermining is a potential pitfall that may mimic a tear of the distal attachment of the volar plate. Coronal (B) and axial (C) T2-weighted images demonstrate the normal appearance of the cordlike collateral ligaments.

Collateral ligament injuries result from excessive valgus or varus force and are described as a sprain, seen as capsular thickening and adjacent edema, or as a partial- or full-thickness tear or avulsion. Small avulsion fractures can occur at either the proximal or the distal attachment site (Fig. 10-5).

Figure 10-5 Interphalangeal joint capsular injury. Coronal T1-weighted (A) and T2-weighted (B) images show mild thickening of the midsubstance of the radial collateral ligament (RCL) with a complete avulsion at its proximal attachment site. The lack of adjacent soft tissue edema indicates that this injury is either subacute or chronic.

Dorsal dislocation of an interphalangeal joint is such a common injury across the entire array of athletic pursuits that it has been referred to as “coach’s finger.” Dorsal dislocations occur most commonly at the level of the proximal interphalangeal joint but also occur at the distal interphalangeal joint (Fig. 10-6). Dorsal dislocation can result in an injury to the volar plate and is often associated with a fracture of the volar aspect of the base of the dislocated phalanx (Fig. 10-6C). Fractures/dislocations are usually treated with dorsal splinting, with the interphalangeal joint in mild flexion to allow healing of the fracture and injured soft tissue structures. Fractures that involve more than 50% of the articular surface of the base of the dislocated phalanx are considered unstable and require open fixation.

Figure 10-6 Coach’s finger. Dorsal dislocation of the proximal interphalangeal joint. Anteroposterior (AP) (A) and lateral (B) views of the proximal interphalangeal (PIP) joint show dorsal dislocation of the PIP. This is the most common injury resulting in disruption of the volar plate at the level of the PIP or distal interphalangeal joint. C, Lateral radiograph shows a small avulsion fracture involving the base of the middle phalanx, which may be seen following interphalangeal dislocation. Involvement of more than 50% of the articular surface usually requires open fixation.

MRI of the interphalangeal joints is performed in a similar manner as previously described for the metacarpophalangeal joints, with coronal and axial imaging planes best suited for the evaluation of the collateral ligaments and sagittal and axial imaging planes best suited for evaluation of the volar plate injuries. In addition to a description of the extent of soft tissue injury, it is important to search for adjacent osseous injuries and to describe avulsion fractures or involvement of the adjacent articular surface.

Flexor Tendons and Pulley System

Flexion of the digits is accomplished by a complex system of muscles, tendons, pulleys, and vincula. A basic knowledge of this complex anatomy is crucial if one is to adequately describe injuries involving these structures. The flexor pollicis longus tendon exits the carpal tunnel at the level of the base of the first metacarpal and passes obliquely between the opponens pollicis and the oblique head of the adductor pollicis, enters a synovial sheath, and then inserts on the volar aspect of the base of the distal phalanx of the thumb.

Flexion of the second through fifth digits is accomplished by the combined action of two tendons, the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP). The two flexor tendons travel together with the FDP tendon located just deep to the FDS tendon as they exit the carpal tunnel at the level of the wrist and enter the hand. The tendons then enter a common digital flexor tendon sheath at the level of the metacarpophalangeal joint. Prior to the level of the proximal interphalangeal joint, the flexor superficialis tendon splits into two slips and allows passage of the flexor profundus tendon, which becomes superficial at this level. The separate tendon slips of the superficialis tendon then reunite deep to the profundus and insert as radial and ulnar slips onto the palmar aspect of the base of the middle phalanx. This normal splitting and reuniting or decussation of the FDS tendon to allow passage of the FDP tendon has been referred to as the camper’s chiasm (Fig. 10-7). After passing through the decussation, the FDP tendon continues distally to attach on the base of the distal phalanx. This anatomic configuration allows the FDS tendon to control flexion of the proximal interphalangeal joint, while the FDP tendon controls flexion at the level of the distal interphalangeal joint (Fig. 10-8).

Figure 10-7 Flexor tendon anatomy. Decussation or splitting of the flexor digitorum superficialis tendon (camper’s chiasm) at the level of the proximal interphalangeal joint allows passage of the flexor digitorum profundus tendon, which continues on to attach on the base of the distal phalanx.

Figure 10-8 Flexor tendon anatomy at the level of the proximal interphalangeal (PIP) joint. The normal anatomy of the flexor tendons. The flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP) tendons are indistinguishable from one another in the sagittal imaging plane (A) whereas the axial imaging plane (B) nicely demonstrates the separate FDS tendon slips, allowing passage of the FDP tendon at the level of the PIP joint. MCP, metacarpophalangeal.

A complex system of fibrous bands or retinacular sheaths, referred to as “pulleys” is responsible for maintaining the proper position of the flexor tendons firmly against the volar aspect of the phalanges and prevents “bowstringing” of the tendons during flexion of the finger. The pulley system is composed of five annular and three cruciate pulleys. The annular pulleys (primarily A2 and A4) are vital for normal digital function (Fig. 10-9). They prevent tendon bowstringing and also ensure optimal joint flexion for a given amount of tendon excursion. The cruciate pulleys are primarily responsible for maintaining the proper flexibility of the tendon sheath, thus allowing the sheath to conform to the various shapes required for normal digital flexion. The cruciate pulleys also allow access of the digital arteries, which provide the tendon blood supply (Fig. 10-10).

Figure 10-9 Normal anatomy of the flexor tendon pulley system.

Figure 10-10 MR appearance of the flexor tendon pulley system. Sagittal and axial images show the normal MR appearance of the flexor tendons, their supporting pulley mechanism, and the relation of one to the other at the various levels. DIP, distal interphalangeal; MCP, metacarpophalangeal; PIP, proximal interphalangeal.

The vinculum system is an arrangement of triangular fibrous bands that extend from the dorsal surface of the flexor tendons of the digit to the nearby capsule of the interphalangeal joint and the adjacent phalanx. These fibrous bands are located just proximal to the insertion of the tendon to the underlying bone and are responsible for conveying small vessels to the tendons. The vinculum breve superficialis provides the blood supply for the FDS at the level of the proximal interphalangeal joint, whereas the vinculum breve profundus provides the blood supply for the FDP at the level of the distal interphalangeal joint.

The range of abnormalities involving the flexor tendons includes tenosynovitis of the tendon sheath, which may be sterile or infectious. Sterile tenosynovitis often results from repetitive trauma or can be associated with inflammatory arthropathies such as rheumatoid arthritis. Infectious tenosynovitis is most commonly bacterial in origin but may result from an atypical infectious agent such as mycobacterium. Infectious tenosynovitis is most often associated with a history of penetrating trauma, usually a punch to the mouth. Tendinopathy represents a degenerative process of the tendon that may be age-related or may result from repetitive trauma. Finally, a partial- or full-thickness tear of the tendon may occur. Flexor tendon tears most commonly result from a laceration. Closed tears, though less common, have been shown to be associated with rheumatoid arthritis, osteoarthritis, scaphoid nonunion, Kienböck disease, hook-of-the-hamate fracture, and carpal dislocation. Closed flexor tendon injuries can also result from sudden extension of a flexed joint, and these injuries are commonly seen in rugby and football participants.

Flexor tendon tear or avulsion has been referred to as “jersey finger” because the closed injury often occurs when a player catches his or her finger on an opponent’s jersey resulting in forced hyperextension of an actively flexed finger. The most common pattern of injury is an isolated tear of the FDP, followed by a combined tear of the FDP and FDS; the least common injury is an isolated tear of the FDS tendon. Avulsion injuries of the tendon may be associated with an avulsion fracture, and contraction of the flexor muscle can result in proximal displacement of the osseous fragment. Occasionally, an avulsed osseous fragment arising from the base of the distal phalanx is significantly displaced, sometimes to the level of the proximal interphalangeal joint. As a result, this displacement may mimic an avulsion fracture arising from the base of the middle phalanx.

On MRI, tenosynovitis manifests as fluid contained within the tendon sheath and a peritendinous edema of the involved tendon, and it is best demonstrated on axial T2-weighted images (Fig. 10-11). The tendon maintains normal morphology and intrinsic signal. Tenosynovitis may involve a single or multiple adjacent tendon sheaths and is typically graded as mild, moderate, or severe based on the quantity of fluid within the sheath. Ultrasound also demonstrates thickening of the sheath and fluid within the sheath, and power Doppler demonstrates increased flow and hyperemia of the surrounding soft tissues (Fig. 10-12

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