Hand – Anatomy and MRI Optimization

Gorbachova, Tetyana; Atinga, Angela; Probyn, Linda

doi:10.1007/978-3-030-81612-4_10

Tetyana Gorbachova²,
Angela Atinga³ &
Linda Probyn³

1197 Accesses

Abstract

Magnetic resonance imaging (MRI) of the hand represents a unique challenge due to highly complex regional anatomy. This chapter provides a synopsis on normal hand anatomy with review of main organizational principles and structure-function relationship of the osseous and capsuloligamentous structures, musculature and tendons, and their appearance on MRI.

Normal MRI anatomy of the flexor and extensor apparatus of the fingers and thumb and anatomic zones of the extensor and flexor tendons are reviewed in greater detail. Key anatomic variations in the anatomy of the thumb are discussed separately. MRI optimization strategies for clinical MRI examination of the hand, fingers, and thumb are discussed.

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Modern low-field MRI

Article Open access 21 February 2024

Magnetic Resonance Imaging Artifacts

MR Imaging for the Orthopedic Surgeon

Keywords

Normal MRI Anatomy of the Hand

Capsular Anatomy

Overview

The capsular anatomy of the metacarpophalangeal (MCP) joint, proximal interphalangeal (PIP) joint, and distal interphalangeal (DIP) joints is organized in a similar fashion; lateral capsular reinforcements are provided by the proper and accessory collateral ligaments on the radial and ulnar sides of the joint, and the volar capsule is comprised of a thick fibrocartilaginous structure, referred to as the volar or palmar plate (Fig. 10.1). The proper and accessory collateral ligaments share their proximal site of attachment at the proximal osseous aspect of the joint, whereas distally the proper collateral ligaments insert on the distal osseous margin of the joint and accessory collateral ligaments fan out in palmar direction to broadly insert on the volar plate [1, 2] (Fig. 10.2). The volar plates of the lesser MCP joints are connected by the deep transverse metacarpal ligament (DTML) [3]. On MRI, the coronal plane provides best visualization of the proper collateral ligaments, the sagittal plane best depicts the volar plate, and the axial images add visualization of both structures and accessory collateral ligaments. In addition to capsuloligamentous structures, the extensor and flexor system of the finger is essential to the stability to the MCP, DIP, and PIP joints.

The lesser carpometacarpal (CMC) joints can be divided into two groups separated by the ligamentous attachments between hamate and fourth metacarpal and occasionally enclosed in separate synovial cavities: second and third CMC joints and fourth and fifth CMC joints. Functionally, the first and second CMC joints are nearly immobile. There is a short range of gliding at the fourth and fifth CMC joints with a small degree of flexion and rotation. The CMC joints are stabilized by dorsal, volar, and interosseous ligaments [4].

Hand Musculature

Extrinsic muscles acting on the hand originate in the forearm and elbow, and their tendons pass through the wrist to insert on the hand. Intrinsic hand muscles are located within the hand itself. The intrinsic muscles are subdivided into three groups: thenar muscles (discussed separately), hypothenar muscles, and central group. The hypothenar group includes palmaris brevis, abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi muscles. The central group, sometimes referred to as deep or metacarpal muscles, is comprised of lumbrical, palmar interossei, and dorsal interossei muscles. The interosseous muscles arise from the metacarpal bones and insert directly on to the proximal phalanx and to the dorsal aponeurosis of each finger. Three palmar interosseous muscles adduct the fingers at the MCP joints to the long axis of the middle finger. Four dorsal interosseous muscles function to abduct fingers at the MCP joints in relation to the long axis of the middle finger, resulting in spreading of the fingers. The dorsal interossei are bipennate muscles, with each muscle arising from the two adjacent metacarpal bones. The four lumbrical muscles are unique in that they have both a tendinous origin and insertion, originating from the flexor digitorum profundus tendons and inserting on the dorsal aponeurosis.

On an axial image obtained at the level of the mid hand, the lumbrical muscle bellies are recognized along the radial and slightly volar aspect of the flexor digitorum profundus tendons. The interosseous muscles are further dorsal in location with their muscle bellies filling the intermetacarpal spaces. At the level of the MCP joint, the tendons of the intrinsic hand muscles can be identified by their relationship to the DTML: the lumbrical tendons are located superficial to the DTML, while the interosseous tendons are deep to the DTML [3, 5] (Fig. 10.3).

Extensor Apparatus

The complex anatomy of the flexor and extensor tendons of the hand is better understood by considering their different biomechanical requirements. The organization of the extensor apparatus is dictated by the functional demands for stability and integrated functioning [6]. Therefore, compared to the flexors, the extensor apparatus has a much more delicate aponeurotic character [2, 5]. The extensor tendons and retinacular structures form a plexiform construct around the finger that has been likened to a Chinese finger trap or a functional homolog of an exoskeleton [7] (Fig. 10.4). Dorsal aponeurotic sheets of tissue represent the meeting point of tendons associated with different muscles and allow coordination between the extrinsic (extensor digitorum communis (EDC), extensor indicis, extensor digiti minimi) and intrinsic (lumbrical and interosseous) muscles [1, 8, 9]. The EDC trifurcates at proximal phalanx to form a central slip, which inserts on the base of the middle phalanx, and two flanking lateral slips. The lateral slips join the two lateral bands, formed by interossei and lumbrical tendons, to form conjoint tendons. The interossei and lumbrical tendons also give off the medial bands that connect with the central slip distally near its insertion. Conjoint tendons merge distally to form a terminal extensor tendon which inserts on the base of distal phalanx (Fig. 10.4).

At the dorsum of the hand, stabilizing retinacular structures are represented by juncturae tendinum, fibrous bands that connect the slips of the extensor digitorum [10] (Fig. 10.3). There is considerable anatomic variability of the extensor apparatus that includes variations in extensor tendons and juncturae, more common toward the ulnar side of the hand [10].The index finger is more independent as it is critical for a delicate precision grip, so it has the least variable extensor tendon anatomy and the least prominent juncturae [6].

In the finger, the principal stabilizing retinacular structure is referred to as the extensor hood or dorsal aponeurotic expansion [8]. The sagittal band is an important part of the extensor hood at the level of the MCP joint (Figs. 10.1 and 10.5). A thicker deep layer and very thin superficial layer of the sagittal band envelope the extensor tendon and continue around either side of the joint to connect to the volar plate, stabilizing the extensor tendon over the MCP joint [1, 11] (Figs. 10.1 and 10.5). Distal to the sagittal bands, the extensor hood is formed by transverse and oblique fibers which arise from the interossei and lumbricals tendons. At the proximal interphalangeal (PIP) joint, a structure analogous to the sagittal band is referred to as the transverse retinacular ligament and connects the conjoint lateral bands to the flexor sheath. Further distally, a “mini hood” is formed by oblique retinacular ligaments and a triangular ligament that bridges the conjoint tendons.

Flexor Apparatus

Morphologic features of the flexor apparatus are dictated by their functional demands of power and precision. Flexion of the fingers can be carried further than extension as fingers can generally be flexed toward the palm at three neighboring joints. In extension, however, fingers are merely returned to a straight position. Greater excursion of the flexor tendons necessitates additional anatomic structures to prevent tendons bowstringing and facilitate gliding of the tendons [6, 12]. The flexor tendons run through fibro-osseous tunnels that are lined by synovium. The floor or dorsal aspect of each tunnel is composed of palmar surfaces of the proximal and middle phalanges, DTML, and volar plates of the MCP, PIP, and DIP joints. The palmar aspect is formed by fibrous sheets attached to the periosteum of the phalanges and to the volar plates. Local thickenings of these fibrous sheaths are referred to as pulleys [13, 14].

The flexor tendons of the second through fifth fingers include the flexor digitorum profundus (FDP) tendon that inserts at the volar base of the distal phalanx and flexor digitorum superficialis (FDS) that inserts on the midportion of the middle phalanx. At the level of the metacarpal head and proximally FDS lies superficial to the FDP. Distal to the metacarpal, the FDS tendon splits forming a ring aperture to allow passage of the FDP which subsequently becomes the more superficially located tendon. The two portions of the FDS reunite at Camper’s chiasm located deep to the FDP [3]. The advantage of this anatomic arrangement is that in addition to pulleys, the tendons themselves contribute to maintaining their position close to the bone as one tendon forms a sling for the other (Fig. 10.6).

Pulleys maintain close apposition of the tendon to the bone and help flexor tendon tracking. The finger pulley system is composed of annular and cruciform pulleys (Fig. 10.7). Annular pulleys serve to stabilize the tendon during motion, while cruciate pulleys facilitate deformation of the tendon sheath during flexion. Annular pulleys are identified on MR imaging as transversely oriented well-defined areas of tendon sheath thickening [15]. The odd-numbered pulleys, A1, A3, and A5, are located at the level of the MCP, PIP, and DIP joints, respectively. Cruciform pulleys are delicate crisscrossing web-like fibers interposed between annular pulleys and not typically visualized on clinical MR imaging. The most biomechanically important and most frequently injured pulleys are the A2 and A4 pulleys. The A2 is the longest pulley, covering the proximal two thirds of the proximal phalanx. The A4 pulley covers the midportion of the middle phalanx [15]. Annular pulleys are best depicted on axial MR images as thin low signal intensity struts anchoring the flexor tendons to the volar plates at the level of the joints or to the volar surface of the bone along the phalangeal osseous attachments. On sagittal images, the annular pulleys can be observed as local thickenings of low signal intensity along the palmar aspect of the tendon sheaths. The locations of cruciform pulleys can be indirectly demonstrated as areas of pleating of the synovial sheaths near the PIP and DIP joints in the presence of tenosynovitis (Fig. 10.7).

On MRI, the interplay between the FDS and FDP is best followed on sequential axial images. Additional longitudinal assessment of the tendons and their insertions is performed in the sagittal plane (Figs. 10.6 and 10.7). When following the course of the flexor tendons on axial images, it is important to remember that they are true to their names within the wrist and hand. Distal to the A1 pulley, the FDS divides into radial and ulnar slips, and along the course of the A2 pulley, the superficialis and profundus tendons swap their locations so that further distally FDS is located deep to FDP [15]. The FDP tendon may display a median longitudinal groove or two separate slips [16] (Fig. 10.8).

Synovial sheaths provide nutrition and lubrication to the tendons. To enable greater longitudinal excursion of the flexor tendons in the wrist and hand, the flexor synovial sheaths extend beyond the boundaries of the corresponding retinacular structures. Because the metacarpal bones of the thumb and little finger have the greatest mobility compared to other fingers, their flexor tendon synovial sheaths pass without interruption from fingers to the wrist [12]. The synovial sheaths of the thumb and little finger often communicate with the radial and ulnar bursae at the wrist, respectively. The flexor tendon sheaths of the index, long, and ring fingers typically do not have as great a proximal extent; these sheaths begin at the level of the metacarpal necks proximal to the DTML and terminate distally at the insertion of the FDP. The multiple anatomic variations in communications of the palmar bursae and finger tendon sheaths may necessitate imaging of the entire hand and wrist when evaluating pathology affecting the synovial sheaths, in particular infection [17, 18].

Vascular and Digital Nerve Anatomy

Overview

Arterial blood supply to the hand is provided by a superficial palmar arch, formed by anastomosis between the continuation of the ulnar artery and superficial volar branch of the radial artery, and the more proximal deep palmar arch, formed by the deep branch of the radial artery as it passes from dorsal to the deep volar hand and anastomoses with one or both deep volar branches of the ulnar artery. The superficial palmar arch has greater anatomic variability with several patterns of complete or incomplete arch described in the literature [19]. Common digital arteries originate from the superficial arch. Each finger has two palmar digital arteries that originate from the bifurcation of the common digital artery at the level of the base of the proximal phalanx and course along the radial and ulnar side of the flexor tendon sheath dorsal to the proper digital nerves [20] (Fig. 10.9). Communicating branches of the digital arteries form three transfers of palmar arches in the finger: proximal, middle, and distal. The pulp of the finger and nail matrix are nourished by the matrix arches and longitudinal arteries.

In the regions where tendons are surrounded by true synovial sheaths, the vessels enter the tendon via mesotenon that, along with synovial fluid, provides a nutritional pathway to the tendon. In digital flexor tendons, the blood supply is delivered via thin strands of synovium called the vincula tendinum. The vincula carry minute vessels and connect to the dorsal part of the tendons (Fig. 10.10). In the digital canal, each flexor tendon typically has two kinds of vincula, the short and the long. The short vincula of FDS and FDP (vinculum breve superficialis and vinculum breve profundus) are found consistently in all fingers. The long vincula (vinculum longum superficialis and vinculum longum profundus) may vary in type and differ in each finger [21].

The motor and sensory innervation of the hand is provided by three nerves: median, ulnar, and radial nerves [20, 22]. Variations from the classical nerve distribution are extremely common in the hand. Distal to the transverse carpal ligament, the median nerve gives off a short recurrent motor branch for the thenar musculature and continues as three common digital nerves. The first common digital nerve divides into three proper volar digital nerves supplying the thumb and radial side of the index finger. The second and third common digital nerves each divide into two proper digital nerves that supply the ulnar side of the index finger, both sides of the third finger, and radial side of the fourth finger. Each proper digital nerve gives off a dorsal branch that joins the dorsal digital nerve from the superficial branch of the radial nerve and supplies the dorsal aspect of the distal phalanx. At Guyon’s canal, the ulnar nerve divides into the deep motor and superficial sensory branches. The superficial sensory branch of the ulnar nerve continues in a straight course and divides into the fourth common digital nerve that supplies the ulnar side of the fourth ray and radial side of the little finger and a proper palmar digital nerve that supplies the ulnar side of the little finger. The deep motor branch of the ulnar nerve crosses the palm and innervates intrinsic hand muscles including all the interossei muscles and third and fourth lumbrical muscles. The innervation of the thenar musculature is provided by the median nerve and deep branch of the ulnar nerve, while hypothenar musculature is entirely supplied by the deep ulnar nerve. The superficial branch of the radial nerve divides into dorsal digital nerves that provide sensation to the radial aspect of the dorsum of the hand, dorsum of the thumb and index and long fingers, and dorsal radial side of the ring finger.

Recent studies have demonstrated that hyperintense palmar subcutaneous nodules in the hands and proximal fingers frequently observed on clinical MRI examinations represent normal Pacinian corpuscles and should not be mistaken for pathological conditions [23, 24]. The corpuscles are sensory receptors for vibration and deep pressure. On MRI, they appear as round or oval, 1–5 mm in diameter, non-enhancing, T2-hyperintense subcutaneous nodules, separate from the vessels, concentrated in subcutaneous fat of palms around the MCP joints (Fig. 10.11).

Anatomic Zones of the Extensor and Flexor Hand Tendons

To provide an organized approach to the anatomic structures and lesion localization, a topographic classification of zones has been developed for the flexor and extensor tendons. According to the Kleinert and Verdan classification, the hand and wrist encompass five flexor and eight extensor zones that are numbered distal to proximal [25].

The extensor zones alternate between the joint lines (odd-numbered zones) and the areas in between the joints (even-numbered zones) (Fig. 10.12). The topographic division of the flexor tendons into the zones takes into account the interplay between the FDP and FDS, presence of the pulleys and synovial sheaths, and vascular supply delivered via vincula (Fig. 10.13). Of particular importance is flexor Zone II that spans a relatively large area at the palmar aspect of the finger (Fig. 10.14). Zone II starts distal to the insertion of the FDS at the volar base of the middle phalanx and stops proximally at the distal palmar fold, which corresponds to the proximal margin of A1 pulley on MRI. Due to the complexity of this region, injuries to flexor Zone II carry worst prognosis and used to be called “no man’s land.”

Normal MR Imaging Anatomy of the Thumb

Osseous and Capsuloligamentous Anatomy of the Thumb

Thumb CMC Joint

The first CMC joint is a unique semi-constrained biconcave saddle joint between the base of the first metacarpal and distal surface of the trapezium [26, 27]. The joint has a wide range of movement and is inherently unstable, requiring many ligaments for support [28, 29]. Although up to 16 ligaments have been described in cadaveric hands, only some of these ligaments provide most of the stability at the CMC joint and are visible on MRI (Fig. 10.15). For a dedicated thumb CMC joint MRI, the imaging planes are prescribed to the thumb, as described later under MRI optimization [27].

The dorsal ligament complex, also referred to as the dorsal deltoid ligament, is best seen on sagittal MR images of the thumb. The dorsal deltoid ligament is comprised of three ligaments: the dorsal radial ligament (DRL), dorsal central ligament (DCL), and posterior oblique ligament (POL). The DRL attaches to the dorsal radial tubercle of the trapezium and the dorsal edge of the first metacarpal base, adjacent to the abductor pollicis longus (AbPL) tendon. This is the thickest ligament and most easily seen on MR images [30]. The DCL is adjacent to the DRL, being more dorsal and ulnar [31]. The POL attaches to the dorsal trapezium and dorsal base of the first metacarpal. These dorsal ligaments act as a primary restraint to dorsal radial metacarpal dislocation [27, 32]. Given their broad range of attachment and support provided, the dorsal ligaments have been likened to a deltoid-type structure [28]. The intermetacarpal ligament (IML) attaches to the dorsal aspect of the first and second metacarpal bases and restrains thumb movements, particularly abduction. It can be difficult to see on MR imaging but is most visible on coronal images [30] (Figs. 10.15 and 10.16).

The volar ligament complex is thinner than the dorsal ligaments but still functionally important and is best seen on sagittal MR images (Fig. 10.16e, f) [30]. The most important volar ligament is the anterior oblique ligament (AOL), also called the beak ligament, which attaches to the volar tubercle of the trapezium and to the volar tubercle, or a “beak,” of the thumb metacarpal. AOL has superficial and deep components [30] (Fig. 10.16f).This ligament resists volar or dorsal stress [26, 27, 32]. The ulnar collateral ligament (UCL) attaches proximally to the trapezium along the distal and ulnar margins of the flexor retinaculum and distally to the volar ulnar base of the first metacarpal [30]. The UCL of the first CMC joint can be difficult to visualize on MR imaging.

Thumb MCP Joint

The thumb MCP joint is a condyloid joint which allows flexion, extension, adduction, abduction, and circumduction. The most common location of sesamoid bones in the hand is at the first MCP joint [33]. Sesamoid bones act as a pulley system that provides tendons with a smooth surface over which to glide [33]. The flexor pollicis brevis (FPB) tendon inserts onto the radial sesamoid bone and the radial base of the proximal phalanx of the thumb, whereas the adductor pollicis (AdP) tendon inserts onto the ulnar sesamoid bone and ulnar base of the proximal phalanx [30]. The volar plate is a wedge-shaped fibrocartilage plate that reinforces the volar joint capsule and extends between the two first MCP sesamoid bones [30, 33] (Fig. 10.17).

The radial collateral ligament (RCL) and ulnar collateral ligament (UCL) are the primary stabilizers to varus and valgus stresses of the MCP joint, respectively [30]. The proper RCL and UCL originate at the dorsal aspect of the first metacarpal head and insert at the volar aspect of the first proximal phalangeal base. The accessory RCL and UCL are adjacent to the volar aspect of the proper collateral ligaments and extend from the metacarpal heads to the volar plate and sesamoid bones. The proper and accessory collateral ligaments are taught reciprocally during flexion and extension [34]. Palmar ligaments extend from the metacarpal head to the sesamoid (metacarpal sesamoid ligament) and from the sesamoid to the proximal phalanx (sesamoid phalangeal ligament) (Fig. 10.18).

Thumb IP Joint

The interphalangeal joint of the thumb shares the same anatomy as the interphalangeal joints of the lesser digits, discussed earlier in this chapter.

Muscle and Tendon Anatomy of the Thumb

The intrinsic muscles at the thumb form the thenar eminence, the palmar muscular bulge on the radial side of the hand at the base of the thumb. It comprises the opponens pollicis (OP), abductor pollicis brevis (AbPB), and flexor pollicis brevis (FPB) muscles, all originating at the flexor retinaculum (Fig. 10.19). The OP originates from the tubercle of the trapezium and the flexor retinaculum and inserts into the lateral margin of the first metacarpal. It medially rotates the thumb with flexion at the first CMC joint permitting opposition. The AbPB arises from the scaphoid and trapezium tubercles and the flexor retinaculum. It is superficial to the OP and inserts at the lateral base of the proximal phalanx of the thumb and abducts the thumb. The superficial head of the FPB arises from the tubercle of the trapezium and flexor retinaculum, passing along the radial margin of the flexor pollicis longus (FPL) tendon. The deep head, if present, arises from the trapezoid and capitate and the transverse carpal ligaments of the distal carpal row. It lies just radial to the abductor pollicis muscle and permits flexion at the MCP joint. Both heads of the FPB insert on the radial base of the proximal phalanx of the thumb and first MCP radial sesamoid. The deep head of the FPB is innervated by the deep branch of the ulnar nerve, and the remainder of the thenar muscles is innervated by the recurrent branch of the median nerve. Although the adductor pollicis (AdP) muscle does not belong to the proper thenar or the central muscle groups, it oftentimes grouped with a thenar musculature. The AdP has oblique and transverse heads that originate from the palmar aspect of the second and third metacarpal bones. AdP inserts onto the base of the first proximal phalanx, ulnar sesamoid, and adductor aponeurosis (see below) and receives innervation from the deep branch of the ulnar nerve.

The extrinsic flexor muscle group includes the FPL, AbPL, extensor pollicis brevis (EPB), and EPL muscles. The FPL muscle originates at the volar surface of the radius and the adjacent interosseous membrane. It has a long tendon that passes under the flexor retinaculum through the carpal tunnel, located dorsal and radial to the median nerve [30]. The FPL tendon passes between the thenar and AdP muscles. The distal tendon lies superficial to the volar plate between the two sesamoid bones at the MCP joint and inserts distal to the base of the distal phalanx of the thumb (Figs. 10.19 and 10.20). The FPL tendon flexes the IP joint and to a lesser degree the MCP joint. The FPL lacks a vinculum and adjacent lumbrical muscle that support the digital flexor tendons; therefore, the tendon has even less restriction and is more likely to retract if torn.

The first and third extensor tendon compartments have tendons that are important for thumb movement. In compartment one, the AbPL and EPB tendons are important for thumb abduction, extension, and rotation at the first CMC and MCP joints [30]. In the third extensor tendon compartment, the EPL tendon passes on the ulnar side of Lister’s tubercle of the radius before extending distally and is responsible for extension of the interphalangeal joint.

The extensor mechanism is simpler in the thumb than in other digits [15]. The EPB tendon inserts to the dorsal base of the proximal phalanx and blends to the dorsal plate of the first MCP joint. The EPL tendon continues to the dorsal base of the distal phalanx. The EPB is variable and can continue to attach to the distal phalanx along with the EPL tendon [35]. The dorsal plate does not have well-defined attachments to the metacarpal and proximal phalanx, and a synovial recess may be seen deep to the dorsal plate and EPB insertion, mimicking a dorsal plate injury [36]. The thumb extensor tendons do not branch into central and lateral slips as in the digits [30].

The extensor hood is the connective tissue that envelops the extensor tendons and consists of the sagittal band at the level of the MCP joint and the triangular expansion more distally. The sagittal band of the first MCP joint maintains the EPL tendon in the midline and is visible on MR imaging [30] (Fig. 10.20). The triangular expansion is the distal extension of the extensor hood beyond the sagittal band and envelops the EPL tendon as it extends to its insertion to the distal phalanx [30]. It is typically not visible on MR imaging. The AdP aponeurosis contributes fibers to the ulnar side of extensor hood (Fig. 10.20), whereas the AbPB and FPB tendons contribute fibers from the radial side [30]. The AdP aponeurosis overlies the UCL in a somewhat oblique plane and has an attachment to the EPL tendon (Figs. 10.20 and 10.21). The close relationship of the AdP aponeurosis and UCL predisposes to a stener lesion, where the AdP aponeurosis is interposed between a torn retracted UCL and prevents proper ligament healing. The AbPB tendon passes over the radial side of the joint to attach to the radial base of the proximal phalanx. The AbPB aponeurosis overlies the RCL and blends with radial side of the sagittal band and extensor hood (Figs. 10.17 and 10.20) [30]. The sagittal band blends with the collateral ligaments at the periphery at the MCP joint and is indirectly connected to the sesamoid bones and volar plate [30].

Pulleys of the Thumb

The pulleys of the thumb function to keep the FPL tendon in close apposition to the phalanges and only consist of annular pulleys, unlike other fingers [30]. The first annular pulley (A1) is at the level of the MCP joint. It is a transverse retinacular structure that covers the MCP joint with the proximal two thirds of the volar plate [36]. It is intimately associated with the sesamoid bones [30]. It can be difficult to distinguish on MR imaging. The second annular pulley (A2) is a transverse retinacular structure at the level of the interphalangeal joint and is fused with the volar plate and the base of the distal phalanx [36] (Fig. 10.22).

The oblique annular pulley is located between the first and second annular pulleys at the level of the mid-proximal phalanx and courses obliquely from the ulnar side of the base of the proximal phalanx to the radial side of the base of the distal phalanx [36]. The proximal ulnar attachment of the oblique annular pulley is intimately associated with the attachment of the adductor aponeurosis [37]. The variable annular pulley is located between the first annular and the oblique annular pulley at the level of the proximal phalanx base. The radial limb is longer than the ulnar limb normally (Fig. 10.23) [30].

MRI Optimization

When imaging the hand, fingers, or thumb, MR imaging optimization strategies are focused on (1) proper patient and extremity positioning to ensure both patient’s comfort and image quality, (2) selecting appropriate coverage with respect to the zonal anatomy to answer specific clinical questions, and (3) obtaining high-resolution images in planes prescribed to the region of interest.

For imaging of the fingers, the patient can be positioned supine or decubitus with the hand at the side of the patient (Fig. 10.24). This positioning may not always be achievable due to coil design and patient size. The image quality may also be negatively affected by field heterogeneity when the hand is located at the periphery of the bore of the MR imaging unit. A standard position of the hand in the magnet designed to place the hand close to the isocenter of the bore (the so called superman position, with the patient lying prone with the arm elevated above the head) is often poorly tolerated by patients. The discomfort can be alleviated by propping the patient’s body with pillows to decrease the extension at the shoulder (Fig. 10.25). When bilateral hand MR imaging is requested, for example, for evaluation of inflammatory arthritis, both hands may be placed in the extremity coils and imaged simultaneously in the “prayer position” or “fetal-praying,” allowing assessment of disease symmetry and minimizing the duration of the study (Fig. 10.26) [38, 39]. Padding and splint immobilization can increase comfort and minimize motion.

High-resolution imaging of the small structures in the fingers and thumb requires the use of a local coil. Although the coil should be as small as possible to provide a field of view (FOV) suitable for the area of interest to maximize the signal-to-noise (SNR) ratio, wrist or extremity coils can provide an extended FOV which may be necessary to image the proximal extent of tendons, synovial sheath anatomy, tumor staging, or arthritis screening [40]. When evaluating flexor tendon injuries in particular, the imaging protocol should address both the site of the injury and the potential for significant retraction of the proximal tendon stump. Dependent on the degree of retraction, either extending or moving the FOV proximally may be necessary (Fig. 10.27).

For dedicated imaging of the fingers and thumb, the FOV and slice thickness should be minimized in order to maximize spatial resolution with acceptable SNR. The FOV typically ranges from 6 to 12 centimeters, and slice thickness should be 2–3 millimeters in the sagittal and coronal planes and 3–4 mm in axial planes. The in-plane resolution should be less than 0.5 mm pixel size (FOV divided by the matrix size) [16, 40]. Higher resolution may be achieved with 3T MR imaging units and specially designed local coils. Increasing matrix size to achieve high resolution typically results in increased scanning time that can lead to patient discomfort and motion artifact. Parallel imaging and increase interslice gap may be used to mitigate this and decrease scanning time. Three-dimensional gradient echo sequences produce images of high SNR and spatial resolution and allow creating reformations in multiple planes.

The imaging planes must be prescribed with respect to a finger or a thumb rather than the hand or wrist. For internal comparison, the adjacent finger should be included in the FOV. In dedicated MR imaging of the thumb, the hand should be positioned so that the thumb is aligned parallel to the main magnetic field in a slightly abducted position. An axial image through the head of the first metacarpal and collateral ligaments may be used to prescribe true sagittal and coronal planes of the thumb (Fig. 10.28).

In order to minimize magic angle artifact, the fingers should be extended and aligned with their long axis parallel to the main magnetic field. The exception to this is imaging of an annular pulley injury, where the finger of interest can be imaged at 35–40 degrees of flexion to depict bowstringing of the tendon and provide a useful secondary sign of pulley injury [41, 42].

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Department of Radiology, Einstein Healthcare Network, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA, USA
Tetyana Gorbachova
Department of Medical Imaging, University of Toronto, Sunnybrook Health Sciences Centre, Toronto, ON, Canada
Angela Atinga & Linda Probyn

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Tetyana Gorbachova
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Angela Atinga
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Linda Probyn
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Correspondence to Tetyana Gorbachova .

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Department of Radiology, Imaging Institute, Allegheny Health Network, Pittsburgh, PA, USA
Bethany U. Casagranda

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Gorbachova, T., Atinga, A., Probyn, L. (2022). Hand – Anatomy and MRI Optimization. In: Casagranda, B.U. (eds) MRI of the Upper Extremity. Springer, Cham. https://doi.org/10.1007/978-3-030-81612-4_10

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DOI: https://doi.org/10.1007/978-3-030-81612-4_10
Published: 10 October 2021
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Hand – Anatomy and MRI Optimization

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