Hand and Wrist

Thomas H. Berquist

INTRODUCTION

Imaging of the hand and wrist can be difficult due to the complex bone and soft tissue anatomy. Optimization of the numerous imaging techniques and approaches is essential in today’s cost-conscious environment.¹^,²^,³^,⁴^,⁵^,⁶ Routine radiographs or computed radiography (CR) and fluoroscopically positioned spot films are usually adequate for identification of fractures and other osseous pathology. Subtle changes may require radionuclide studies followed by computed (CT) or conventional tomography to define clearly the nature of bone lesions. Invasive techniques such as arthrography and tenography have been used to identify ligament and tendon injuries.⁷ The role of ultrasound for evaluation of hand and wrist disorders has expanded significantly in recent years. Evaluation of soft tissue abnormalities and osseous lesions is more commonly accomplished with this dynamic and lower cost technique.⁸^,⁹^,¹⁰ CT is the technique of choice for evaluation of complex or subtle fractures, dislocations, and subluxations of the distal radioulnar joint.¹¹ CT arthrography is also a useful tool, especially in patients where MRI may be contraindicated.¹² The role of MRI in the hand and wrist has continued to expand with new pulse sequences, coil technology, and higher field strength magnets [3 Tesla (T) and 8 T]. MR arthrography and MR angiography have contributed to the increased utilization of MRI for evaluation of hand and wrist disorders.¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸

Recent studies have demonstrated the significant impact of MR on treatment approaches. Hobby et al.⁵ demonstrated that MRstudies changed the clinical diagnosis in 55%, modified the treatment plan in 45%, and improved the physicians’ understanding of the disease process in 67% of cases.

TECHNIQUE

Multiple factors must be considered to optimize MR examinations.² Considerations include the presence of metal or electrical devices, the area of interest (small vs. large), patient size, patient condition, the need for sedation, and whether intravenous or intra-articular contrast may be required.²^,¹⁹^,²⁰

Figure 11.1 Patient positioned with the arm at the side and supported for comfort.

Patient Positioning/Coil Selection

MRI examinations of the hand and wrist can be difficult to perform due to limitations in positioning and the demanding anatomic detail required for lesion detection.²^,²⁰^,²¹ Patient comfort is an essential part of the examination. If the position is difficult to tolerate, motion artifact and image degradation will occur. In our initial review of upper extremity MRI studies, we noted motion artifacts or incomplete studies due to patient discomfort in 25% of cases.²⁰

Positioning depends upon patient size, information required (i.e., motion studies), software, and coil availability. When possible, we position the patient with the arm at the side and the hand and wrist in the optimal or most comfortable position (pronation, supination, or thumb up) (Fig. 11.1). The wrist can also be placed over the abdomen with the arm flexed. However, the coil must be separated from the abdominal wall to prevent respiratory motion artifact. Larger patients and children may be positioned in the prone or lateral decubitus position with the arm above the head (Fig. 11.2). In this setting, shoulder discomfort frequently leads to motion artifact and reduced image quality.²⁰^,²¹^,²²

In patients with suspected arthropathy, we may use the praying hands approach to evaluate both hands at the same time (Fig. 11.3). This is a comfortable position for most patients and allows the examination to be performed more quickly.²

Once the hand and wrist are positioned, they should be supported with pads or bolsters to reduce motion and enhance comfort. The exception to this approach is when motion studies are required. In this case, motion control devices can be used to optimize position changes.⁷^,²³

Uniform signal intensity is most easily obtained using new flat or circumferential coil systems (Fig. 11.4).²¹^,²⁴^,²⁵^,²⁶^,²⁷ The small, flat coils (3 and 5 inch) are also adequate for hand and wrist imaging. Flat coils allow more flexibility for positioning and motion studies.² We also use small digital coils for focused examinations of the hand and fingers (Fig. 11.4). Dual coils allow simultaneous evaluation of both hands and wrists when pathology is bilateral or comparison is required.²⁴ Yoshioka et al.²⁷ used 23-mm flat circular microscopy coils to achieve improved spatial resolution and signal-to-noise ratios (SNR) compared to conventional 5-inch coils.

Figure 11.2 Patient positioned for evaluation of the hand and wrist using a circumferential (volume) coil. The arm is above the head. This position is not easily tolerated, and motion artifacts are likely to occur. Shoulder discomfort frequently develops early in the examination.

Optimal image quality for hand and wrist imaging requires a small field of view (FOV) (Fig. 11.5).²¹^,²⁸^,²⁹ We typically use an 8- to 12-cm FOV for examinations with both flat and volume coils. The image matrix should be 256 to 512 with 1- to 3-mm sections (Table 11.1). Smaller sections (0.6 to 1 mm) are used for volume acquisitions and three-dimensional imaging.¹⁹^,³⁰ In general, one acquisition is adequate, though for improved image quality we occasionally use two acquisitions.

Most imaging of the hand and wrist is performed at 1.5 T. However, experience with 3T magnets is increasing. The primary advantage of extremity imaging at 3 T is an increased SNR. The SNR increases linearly with field strength; hence, the SNR at 3 T is twice that of standard systems at 1.5 T. This allows significant improvement in spatial resolution without increasing image time. More detailed anatomic information may be provided for small structures including the ligaments, articular cartilage, and triangular fibrocartilage complex (TFCC) (Fig. 11.6).³¹

We have used custom-designed transmit/receive coils (Fig. 11.4D) with 6-cm internal diameter for fingers and 10-cm diameter for wrists. These coils provide even greater SNR compared to phased array coils. Though experience is early, imaging of the hand and wrist at 3 T may offer advantages over 1.5 T.³¹ Early studies at 7.0 T demonstrate an increase in SNR of 100% compared to 3.0 T.³²

Pulse Sequences/Image Planes

Once the patient has been positioned, the proper pulse sequences and image planes must be selected to demonstrate
the anatomy and characterize the lesion (Table 11.1). An effective screening examination can be accomplished by the beginning with either a coronal or sagittal scout (SE 500-400/10-20). This should include the full area of the hand and wrist to be examined. The sequences and image planes vary with clinical indication. One can begin with a standard screening examination and add additional sequences or gadolinium when indicated. T1- and T2-weighted sequences are performed. We use conventional spin-echo T1-weighted sequences and turbo spin-echo (FSE) T2-weighted sequences with fat suppression in most cases (Table 11.1). Conventional short TI inversion recovery (STIR) sequences have been replaced with FSE inversion recovery sequences. Fluid and pathologic tissues have high signal intensity in comparison to suppressed marrow and fat signal.

Figure 11.3 A: Photo of patient positioned in the lateral recumbent position with hands together in a “praying configuration” so both hands and wrists can be examined at the same time. Sagittal fat-suppressed proton density (B), STIR axial (C), and T1-weighted (D) images obtained in the “praying hands” position. Note the flexor tenosynovitis (arrow) on the left.

Gradient-echo (GRE) sequences can be performed using two- or three-dimensional techniques. We use the latter with sixty 0.6- to 1-mm sections to allow reformatting in any image plane. Ligament, capsular, and articular anatomy are well-defined using this approach.²¹^,³⁰ We are also routinely performing a coronal dual echo steady state (DESS) sequence to evaluate articular cartilage (Fig. 11.7). Multiple (about 100) 1-mm sections can be performed in 6 minutes, 26 seconds. Our screening examination includes all three image planes (axial, coronal, and sagittal). For certain
anatomies, oblique planes are useful (Table 11.2). This is particularly true for the carpal bones (Fig. 11.8) and individual digits of the hand.

Figure 11.4 Coils for hand and wrist imaging. A: Volume quadrature coil. B: Opening volume coil. C: Digital coil for isolated wrist or finger imaging.

Table 11.1 MR Techniques for Hand and Wrist Imaging at 1.5 T

Procedure	Plane	Sequences	Sections/Skip	FOV (cm)	Matrix	Acquisitions NEX
Screening
Wrist	Axial	T1 400-500/10-20	3 mm/0.5	8	512 × 224	1
	Axial	FSE PD 2,400-2,500/20-30	3 mm/0.5	8	256 × 224	1
	Coronal	T1 400-500/10-20	3 mm/0.5	8	512 × 224	1
	Axial	FSE T2 3,500-3,600/70-90	3 mm/0.5	8	256 × 192	1
	Coronal	DESS 24/7, FA 25°	3 mm/0.5	8	256 × 192	1
Hand/finger^a	Coronal	T1 400-500/10-20	1-3 mm/0.5	6	512 × 224	1
	Axial	T1 400-500/10-20	3 mm/0.5	6	512 × 224	1
	Sagittal^a	FSE T2 3,500-4,000/70-90	1-3 mm/0.5	6	256 × 192	1
	Sagittal^a	T1 400-500/10-20	1-3 mm/0.5	6	512 × 224	1
Wrist arthrogram	Coronal	T1 FS 600/18	3 mm/0.5	8	256 × 256	2
	Sagittal	T1 FS 600/18	3 mm/0.5	8	256 × 256	2
	Axial	T1 FS 600/18	3 mm/0.5	8	256 × 256	2
	Coronal	3D GRE 45/9, 30°	1 mm/60/0.5	8	256 × 192	1
Angiogram	Coronal	21/6, 30° or 3.8/1.4, 30°	1 mm/40	8	512 × 256	1
FSE, fast spin echo; PD, proton density; FS, fat suppression; GRE, gradient echo; FOV, field of view; FA, flip angle.
^aflexion and extension.

Figure 11.5 A: Coronal T1-weighted image of the wrist with a 24-cm FOV. T1-weighted image (B) and gradient-echo three-dimensional image (C) with 10-cm FOV. Note the marked improvement in image quality with a small FOV.

Figure 11.6 Coronal T1-weighted 1.5 T (A) and 3 T (B) images of the wrist.

Figure 11.7 Coronal DESS 1.5 T (A) and 3.0 T (B) images demonstrating the articular cartilage.

MR Arthrography

Wrist and hand arthrograms are performed using either indirect (intravenous) or intra-articular injections.

Indirect arthrography has several advantages in that it is minimally invasive, enhances joint fluid (giving an arthrographic effect), and does not require additional time for intra-articular monitoring and injections. Passive or active exercise is performed before imaging to enhance fluid distribution. Using this approach, Schweitzer et al.³³ reported 100% accuracy for detection of triangular fibrocartilage tears and 96% accuracy for identification of scapholunate ligament tears.

Table 11.2 MR Imaging of the Hand and Wrist: Image Planes

Anatomic Structure	Image Plane
Distal radius and ulna	Axial and coronal
	Sagittal for fragment alignment
Distal radioulnar joint	Coronal, axial (neutral, pronation, supination)
Soft tissue proximal wrist	Axial and sagittal
Carpal tunnel	Axial
Carpal bones-scaphoid	Axial and coronal, add oblique sagittal
Metacarpal/phalanges	Axial and oblique sagittal
Tendons	Axial and sagittal
Ligaments	Axial, coronal, and oblique reformats

Disadvantages of indirect arthrography include lack of fluid control (cannot measure joint volume), inability to aspirate fluid, inability to perform diagnostic injections, and inability to do isolated compartment studies.²¹^,³³ The last may make subtle lesions more difficult to detect.

Patients should be preselected so that schedules can be adjusted. Ultrasound, palpation, or fluoroscopy can be used for needle position and injection.²¹^,³⁴ We prefer fluoroscopic monitoring of injections. The radiocarpal, intercarpal, and distal radioulnar joint may all need to be
injected. We begin with the most symptomatic region or area of suspected pathology.⁷^,³⁵^,³⁶^,³⁷

Figure 11.8 Coronal T1-weighted image demonstrating selection of oblique sagittal images to evaluate the scaphoid.

Figure 11.9 Injection site for the radiocarpal joint seen from the posteroanterior (A) and lateral (B) views. Flexing the wrist slightly facilitates needle placement. The needle is angled proximally. The region of the scapholunate ligament should be avoided.

The patient can be seated next to the fluoroscopic table or can be lying supine with the arm extended and hand resting palm down. The latter is preferred to reduce the likelihood of injury should a vasovagal reaction occur during the injection.⁷ The wrist is prepared using sterile technique. The entry site is injected with local anesthetic (1% lidocaine) using a 25-gauge needle. The radiocarpal joint is entered dorsally with the wrist slightly flexed (Fig. 11.9). The extensor tendon and area of the scapholunate ligament should be avoided. The needles should be angled proximally (Fig. 11.9) to avoid the dorsal lip of the radius. Injection of the intercarpal or distal radioulnar joint is performed with the hand flat and palm down (Fig. 11.10). It is necessary that fluid be aspirated and studied before the injection. Three to four milliliters of diluted gadolinium (0.2 mL in 20 mL of 50% iodinated contrast and 50% lidocaine or Marcaine) is injected using fluoroscopic guidance.

When the injection is completed, the patient is transferred to the MR gantry. A phased array wrist coil is used. The patient is positioned as described above. For conventional arthrography, the standard wrist or hand coils are used. When motion studies are required, a positioning device can be used with a non-circumferential coil.²¹^,²³ Conventional sequences and image planes are described in Table 11.1. GRE sequences are used for motion studies.

Figure 11.10 Injection sites for the radiocarpal (1), distal radioulnar joint (2), and intercarpal joint (3). The common carpometacarpal joint (4), first carpometacarpal joint (5), and outer carpometacarpal (6) joints are rarely injected.

Figure 11.11 MR angiogram of the hand and wrist in a patient with vasculitis. There are multiple occlusions and vascular irregularities.

Figure 11.12 Osseous structures of the hand and wrist seen dorsally (A) and from the palmar surface (B).

Sahin et al.³⁸ used three-dimensional spoiled GRE sequences after intra-articular contrast to create virtual arthroscopic images of the triangular fibrocartilage. Image data was transferred to a computer and the images were recreated using navigator software. Preliminary results using this approach were promising.

MR Angiography

Contrast enhanced MR angiography has improved significantly in recent years. Major and digital vessels can easily be demonstrated. Aneurysms, pseudoaneurysms, and vasculitis can be clearly demonstrated (Fig. 11.11).¹⁴^,³⁹^,⁴⁰^,⁴¹ Osseous ischemic changes and vascular tumors are also more readily evaluated.¹⁶^,⁴²^,⁴³

ANATOMY

The osseous and soft tissue anatomy of the hand and wrist is complex. Therefore, in the past, numerous imaging techniques have been required for thorough evaluation. MRI is an additional technique that can provide valuable information regarding subtle soft tissue and bone pathology.⁷^,²⁰^,²¹^,³⁰^,⁴⁴^,⁴⁵^,⁴⁶^,⁴⁷^,⁴⁸^,⁴⁹^,⁵⁰^,⁵¹^,⁵²^,⁵³^,⁵⁴^,⁵⁵^,⁵⁶^,⁵⁷^,⁵⁸ The American College of Radiology Appropriateness Criteria for acute and chronic wrist disorders indicates that radiographs should be the initial screening study. However, MR is indicated for subtle or occult fractures when radiographs are normal, achieving
a ranking of 8 (range 1-9). Similar rankings are achieved for chronic wrist problems and soft tissue injuries.⁴⁴^,⁴⁵

Figure 11.13 A: Sagittal MR arthrogram demonstrating the normal 12° palmar tilt of the distal radius. B: Coronal MR image demonstrating the normal radial inclination angle of 24°. The angle is formed by a line from the styloid tip to the articular margin (a) and a line (b) perpendicular to the radial shaft (r) at the level of the ulnar articular margin. C: Coronal 3.0 T T1-weighted image demonstrating the scaphoid (arrow) and lunate (arrowhead) fossae.

Osseous Anatomy

There are eight carpal bones in thewrist and five metacarpals and fourteen phalanges in the hand (Fig. 11.12). Bones of the wrist form three major articular groups composed of the distal radioulnar joint, the radiocarpal joint, and the midcarpal articulation. The distal radial metaphysis and epiphysis is a largely cancellous bone with only a thin cortical shell that makes this region ideally suited for MRI.⁵⁶^,⁵⁷ The distal radius is elongated on its radial side, forming the radial styloid (Fig. 11.12). Distally the radius has two articular fossae for the scaphoid and lunate, respectively. The distal articular surface normally angles 24° toward the ulna in the frontal plane and 12° to 15° toward the volar in the lateral or sagittal plane (Fig. 11.13). There is a notch in the ulnar side of the radius termed the sigmoid notch that articulates with the distal ulna (Fig. 11.14). Of importance, on the dorsal surface of the radius, are the sulci and palpable dorsal protuberances termed Lister’s tubercle (Fig. 11.14). These osseous changes assist in forming the dorsal compartments for the extensor tendons of the wrist (Figs. 11.14 and 11.15).⁵⁶^,⁵⁷ The cortex in the distal ulna is somewhat thicker than the radius and also has a spikelike projection on the most medial aspect termed the ulnar styloid. There is a groove in the dorsal ulna for the sixth dorsal compartment (extensor carpi ulnaris [ECU]) (Fig. 11.15).⁴⁶^,⁵⁶^,⁵⁸ The head of the ulna articulates with the distal radius via the sigmoid notch and the lunate and triquetrum distally. It is separated from the latter two structures by a TFCC. This will be discussed in detail below.

The carpal bones are composed of three anatomic groups (Fig. 11.12). The proximal row consists of the scaphoid, lunate, triquetrum, and overlapping pisiform. The proximal
surfaces of these bones should form a smooth, unbroken arch in the coronal plane. In the sagittal plane, the angle formed by the scaphoid and lunate should be between 30° and 60°. A second osseous anatomic group, or the distal carpal row, consists of the trapezoid, capitate, and hamate. The third compartment is composed of the trapezium and five metacarpals.²¹^,⁴⁶^,⁵⁶^,⁵⁸

Figure 11.14 Axial T1-weighted image of the wrist demonstrating Lister tubercle, the sigmoid notch (arrows), and the groove in the dorsal ulna for the ECU.

Certain key features of carpal anatomy deserve mention. The scaphoid is the largest carpal bone in the proximal row and serves as a link between the proximal and distal rows (Figs. 11.5, 11.6, 11.7, 11.8). The scaphoid articulates with the radius proximally, lunate medially, capitate distomedially, and the trapezium and trapezoid distally. The scaphoid ridge is locatedonthe mid-surface and accepts80% of the vascular supply to the scaphoid.²¹^,⁵⁶^,⁵⁸

Figure 11.15 Illustration (A) and axial MR image (B) demonstrating the six dorsal compartments of the wrist. I, abductor pollicis longus (APL), extensor pollicis brevis (EPB); II, extensor carpi radialis longus (ECRL) and brevis (ECRB); III, extensor pollicis longus (EPL); IV, extensor digitorum communis (EDC) and extensor indicis proprius (EIP), V, extensor digiti quinti (EDQ); VI, extensor carpi ulnaris (ECU).

The lunate has four articular facets for the radius proximally, the scaphoid laterally, the triquetrum medially, and the capitate distally. Viegas et al.⁵⁹ described the lunate as type 1 or 2, based on the presence of a hamate articular surface. Type 1 (34.5%) has no hamate facet and type 2 (65.5%) has a hamate articular facet (Fig. 11.16).⁵⁹^,⁶⁰

The capitate is the largest carpal bone (Figs. 11.17E, 11.18A, and 11.19B) and plays an important role in the transverse carpal arch. In about 85% of patients, there is a small facet that articulates with the fourth metacarpal base.²¹^,⁵⁶^,⁶¹

The hamate has a prominent palmar projection (hook) (Fig. 11.17E) that forms the medial boundary of the carpal tunnel. This serves as the attachment for the flexor retinaculum.

The trapezium also has four articular facets. On the palmar surface, there is a groove for the flexor carpi radialis tendon and a prominent ridge (trapezial ridge) for attachment of the flexor retinaculum and scaphotrapezial and anterior oblique ligaments (Figs. 11.12 and 11.18A).⁵⁶

The proximal and middle phalanges of the fingers are similar in structure with proximal and distal flaring. The osseous composition of these structures is primarily cancellous. There are two phalanges on the thumb as it lacks a middle phalanx. The remaining digits have three phalanges (Fig. 11.12).⁴⁶^,⁵⁶^,⁵⁸

There are numerous osseous variants.⁶²^,⁶³^,⁶⁴ Identification of these structures, especially ossicles, may be difficult on MR images unless their location is clearly understood or routine radiographs are available for comparison.⁶⁴ Coalitions may occur between the lunate and triquetrum and
capitate and hamate. These may be fibrous, cartilaginous, or osseous.⁶²^,⁶⁴ A more complete discussion of osseous variants is included in the Pitfalls section of this chapter.

Figure 11.16 A: Coronal gradient-echo image demonstrating a type I (single facet) lunate articulating with the capitate. B: Coronal gradient-echo image of the lunate with a second small facet (open arrow, type II) articulating with the hamate. C, capitate; H, hamate; L, lunate.

Ligamentous and Articular Anatomy

The ligamentous anatomy of the wrist is complex due to the stabilization required for the numerous carpal bones and extensive motion (Figs. 11.17, 11.18, 11.19). The orientation of the ligaments about the wrist is also complex, making it difficult to include all of the dorsal or volar ligaments in any one orthogonal MR image plane.³⁰^,⁵⁰^,⁵¹^,⁵²^,⁵³^,⁵⁶^,⁵⁷^,⁶⁵^,⁶⁶^,⁶⁷^,⁶⁸^,⁶⁹ MR images must be obtained using thin sections (= 1 to 2 mm), a small FOV (= 10 cm), and 256 × 256 or 256 × 192 matrix. Three-dimensional Fourier techniques are preferred for thinner contiguous sections, and reformatting can be accomplished. Volar, dorsal, and interosseous ligaments can be defined most consistently with these techniques or MR arthrography.³⁰^,⁵⁰^,⁵¹^,⁵²^,⁵³^,⁵⁴^,⁷⁰

The distal radioulnar joint is primarily stabilized by the TFCC. This complex consists of several components that blend with one another and include the triangular fibrocartilage, the ulnocarpal meniscus, the ulnar collateral ligament (UCL), and the palmar and dorsal distal radioulnar ligaments (Figs. 11.17B, 11.18B, and 11.20). The articular disc is composed of fibrocartilage. The disc attaches to the ulnar margin of the radius with a broader ulnar portion attaching to the ulnar styloid, ulnar fovea, and deep lamina of the antebrachial fascia. The deep lamina is separated from the superficial lamina by the ECU tendon and its sheath.⁵⁶^,⁶⁵ The triangular fibrocartilage (TFC) is most easily identified on coronal images (Fig. 11.18), with the dorsal and volar ligaments most easily seen on axial or three-dimensional images.³⁰^,⁵⁰^,⁵¹^,⁵²^,⁵³^,⁵⁴^,⁷¹^,⁷² The TFC is normally of low signal intensity on MR images. However, degeneration, especially on the ulnar aspect, is common on patients over 50 years of age creating areas of increased signal intensity.⁷³^,⁷⁴^,⁷⁵ Additional support of the distal radioulnar joint is provided by the interosseous membrane between the radius and ulna, the ECU tendon, and the concavity of the sigmoid notch of the radius (Figs. 11.14 and 11.20).²¹^,⁵⁶^,⁶⁵

Wrist stability is provided by the palmar and dorsal ligaments (Fig. 11.21).³⁰^,⁵³^,⁶⁵^,⁷²

Palmar Ligaments

The palmar ligaments consist of two concentric arches originating 1 to 2 mm from the volar margin of the radius and inserting into the proximal carpal row and TFCC (Figs. 11.20 and 11.21).⁵⁸^,⁶⁵ The radioscaphocapitate ligament (Fig. 11.21A) is most lateral, extending from the radial styloid to the scaphoid waist and capitate. At the capitate it joins the ulnocapitate ligament to form the arcuate ligament. The long radiolunate ligament lies medial to the radioscaphocapitate ligament (Fig. 11.21A). The radioscapholunate ligament (ligament of Testut) extends vertically between the short and long radiolunate ligaments to insert on the lunate and medial scaphoid. The short radiolunate ligament extends from the medial radius to the lunate forming the floor of the radiolunate space.⁵⁶^,⁶⁵^,⁶⁷

The palmar midcarpal ligaments include the scaphotrapezium trapezoid, scaphocapitate, triquetrocapitate, triquetrohamate, and pisohamate ligaments (Fig. 11.21A). These ligaments are contiguous, with the radiocarpal and ulnocarpal ligaments joining to form the nearly contiguous palmar capsule.⁵⁶^,⁶⁵

The ulnocarpal ligaments (ulnolunate, ulnocapitate, and lunotriquetral) (Figs. 11.20 and 11.21A) originate primarily from the palmar radiolunate ligament and the TFC.⁶⁵^,⁶⁷

Smith⁵³ was able to define six of the eight palmar ligaments – 1, radioscaphocapitate; 2, radiolunotriquetral; 3, radiolunate; 4, ulnolunate; 5, ulnotriquetral; and 6, triquetroscaphoid – in 95% of wrists. The radioscaphoid and
radioscapholunate were demonstrated in 66% and 26%, respectively. Three-dimensional techniques were used.

Figure 11.17 Axial images of the wrist and proximal hand with illustrations for plane of section. A: Axial images of distal forearm. B: Axial image through the distal radioulnar joint. C: Axial image through radiocarpal joint. D: Axial image through pisotriquetral joint and Guyon’s canal. E: Axial image through the distal carpal row and hamate hook. F: Axial image through the thenar region. G: Axial image through the metacarpals. H: Axial image through the base of the proximal phalanx.

Figure 11.17 (continued)

Dorsal Ligaments

The dorsal radiocarpal ligament is a broad band extending obliquely from the Lister’s tubercle to insert on the lunate and triquetrum. This is the floor of the fourth through sixth extensor compartments (Fig. 11.21B). The dorsal intercarpal ligament (Fig. 11.21B) extends from the triquetrum to insert with three slips onto the scaphoid, trapezium, and trapezoid.⁶⁵

Interosseous Ligaments

The scapholunate and lunotriquetral ligaments are C-shaped (Fig. 11.22), extending from dorsal to proximal to palmar surfaces of the joints.⁶⁵^,⁶⁸^,⁶⁹ The scapholunate ligament is thicker dorsally.⁶⁸^,⁶⁹ Both the dorsal and palmar portions of the lunotriquetral ligament are thicker than the proximal portion.

The scapholunate ligament is low signal intensity in 63% and has areas of intermediate signal intensity in 37% of patients. The ligament may be triangular (90%) or linear (10%) in its configuration (Fig. 11.23).⁵² Signal intensity was low and uniform (type 1) in 49% of wrists. Areas of intermediate signal intensity were noted in 51%. Type 2 central increased signal intensity in the ligament occurred in 14%, type 3 distal increased signal intensity occurred in 16% and proximal type 4 signal intensity occurred in 2% of cases. Intermediate signal intensity extended through the ligament (type 5) in 19% of patients (Fig. 11.23).⁵²

Similarly, the lunotriquetral ligament may also have a linear or triangular configuration with variations in signal intensity in asymptomatic individuals.⁵⁰^,⁵⁶ The lunotriquetral ligament is triangular in 63% and more linear in 37%
of patients. An amorphous appearance was noted in a few patients by Smith and Snearly (Fig. 11.24).⁵⁰ Signal intensity is not always uniformly low, similar to variations described in the scapholunate ligament (Fig. 11.24).⁵⁰^,⁵²

Figure 11.18 Coronal images of the hand and wrist with illustrations for plane of section. A: DESS image of the wrist. B: DESS image through the triangular fibrocartilage. C: Proton density-weighted image through the carpal bones and thenar muscles. D: Proton density-weighted image through the flexor tendons. E: T1-weighted image through the proximal interphalangeal joint.

Figure 11.18 (continued)

The interosseous ligaments in the second carpal row consist of dorsal and palmar transverse interosseous bands (Fig. 11.25). The trapeziocapitate and capitohamate interosseous ligaments have deep ligaments between the articulating surfaces.⁵⁶^,⁶⁵

Ligamentous anatomy of the metatarsophalangeal and interphalangeal (IP) joints is similar with collateral and volar ligaments incorporated into the joint capsule
(Figs. 11.18E and 11.26).²¹^,⁷⁶ These ligaments are tight in extension and relax with flexion of the joints. The collateral ligaments are seen on axial and coronal MR images (Figs. 11.17 and 11.18). The palmar plate is clearly seen on axial and sagittal images.⁷⁶

Figure 11.19 Sagittal images of the hand and wrist with illustrations for plane of section. A: T1-weighted image through the scaphoid. B: T1-weighted image through the lunocapitate region. C: T1-weighted image through the pisiform. D: T1-weighted image through the finger with pulley systems labeled.

Figure 11.19 (continued)

Figure 11.20 A: Distal radius including the scaphoid (S) and lunate (L) fossae and the TFCC. B: Ulnocarpal ligament complex and TFCC are seen dorsally.

Figure 11.21 Palmar (A) and dorsal (B) carpal ligaments. 1, first metacarpal; 5, fifth metacarpal; Tm, trapezium; Td, trapezoid; C, capitate; H, hamate; P, pisiform; L, lunate; S, scaphoid; and T, triquetrum.

Figure 11.22 A: Scapholunate ligament from proximally and a slightly radial perspective. B and C: Coronal gradient-echo MR arthrogram images at different levels demonstrating variation in thickness of the scapholunate and lunotriquetral ligaments.

Figure 11.23 Signal intensity patterns in the scapholunate ligament described by Smith.⁵² Type I, uniform low signal intensity; type II, central intermediate signal intensity; type III, distal intermediate signal intensity; type IV, proximal intermediate signal intensity; type V, intermediate signal intensity extending through the ligament.

Muscular Anatomy

Many of the muscles and tendons that cross the wrist originate at the elbow and forearm. These myotendinous units are discussed in Chapter 10. The muscles of the forearm, which are largely responsible for flexion and extension of the wrist, are thoroughly discussed in Chapter 10. Therefore, except for essential anatomy, they will not be reviewed here.⁷⁷ This section will primarily deal with those muscles directly related to bones of the hand and wrist with regard to their origins and insertions (Table 11.3).

The chief flexors of the wrist are the flexor carpi radialis and flexor carpi ulnaris. The palmaris longus is a minor flexor of the wrist (Fig. 11.27).⁴⁶^,⁵⁶ Extension of the wrist is largely due to the extensor carpi radialis longus and brevis and the ECU (Fig. 11.27). During radial deviation of the wrist, primary muscles involved are the abductor pollicis longus and extensor pollicis brevis. Ulnar deviation of the wrist is accomplished primarily by the ECU.⁴⁶^,⁵⁶^,⁷⁸^,⁷⁹

Figure 11.24 Signal intensity variations in the lunotriquetral ligament described by Smith and Snearly.⁵⁰ Type I, homogenous low signal intensity; type II, distal intermediate signal intensity; type III, intermediate signal intensity extending through the ligament; type IV, proximal intermediate signal intensity.

Figure 11.25 Palmar (A) and dorsal (B) intercarpal ligaments.

There are typically four lumbrical muscles that arise from the flexor digitorum profundus tendons and extend along the radial aspects of the second through fifth metacarpals to insert in the extensor aponeurosis of the proximal phalanx on the radial side. The muscles can be identified in the axial and coronal planes (Figs. 11.17 and 11.18). The lumbricals are seen as a tissue of muscle signal intensity between the flexor digitorum profundus tendons proximally and along the radial aspect of the metacarpals adjacent to the interosseous muscles more distally.⁴⁶^,⁵⁶ Insertions are not usually clearly defined on MRI. The flexor pollicis longus is discussed in Chapter 10; however, its function is important in the hand and wrist, so certain aspects of its anatomy need to be repeated. As noted in Table 11.3, the muscle originates from the anterior aspect of the middle third of the radius.⁵⁶^,⁸⁰ The tendon passes through the radial side of the carpal tunnel (Fig. 11.17) radial to the superficial and deep flexor tendons (Figs. 11.17, 11.18, and 11.27). A synovial sheath of the flexor pollicis longus tendon begins just proximal to the flexor retinaculum and extends distally to near the insertion of the tendon on the distal phalanx of the thumb (Table 11.3).⁴⁶^,⁵⁶

Figure 11.26 Metacarpophalangeal (A, B) and interphalangeal (C, D) joint anatomy.

The interosseous muscles form the deepest layer of the muscles in the hand and are divided into palmar and dorsal groups (Fig. 11.17). The palmar group consists of three muscles that take their origin on the radial aspect of the fifth and fourth metacarpals and the ulnar aspect of the second metacarpal. The muscles pass distally between the metacarpophalangeal (MCP) joints to insert on the extensor aponeurosis. The dorsal interossei originate from adjacent metacarpals, the first arises from the first and second metacarpals, the second from the second and third, the third from the third and fourth, and the fourth from the fourth and fifth metacarpal diaphysis. The muscles pass dorsally and distally to insert with a palmar and dorsal slip into the bases of the proximal phalanges. The interosseous muscles, both palmar and dorsal, are innervated by the deep branch of the ulnar nerve. The interosseous muscles aid in abduction and adduction of the fingers of the hand (Table 11.3).⁵⁶

The thenar eminence or muscle group is comprised of the abductor pollicis brevis and superficial head of the flexor pollicis brevis that overlie the opponens pollicis (Fig. 11.17). The abductor pollicis brevis arises from the flexor retinaculum and has deeper origins from the trapezium and trapezoid. This somewhat triangular muscle extends distally to insert in the radial aspect of the proximal phalanx of the thumb. It serves as the primary abductor of the thumb. The flexor pollicis brevis has two heads, one superficial and the other deep. The superficial head arises from the trapezium and flexor retinaculum and the deep head from the
trapezoid. The muscle extends distally to form a tendon that inserts on the radial flexor side of the base of the proximal phalanx of the thumb. The primary function is flexion and rotation of the thumb. The opponens pollicis is partially covered by the abductors and flexors of the thumb and arises from the flexor retinaculum and trapezium to insert on the radial surface of the diaphysis of the first metacarpal. The adductor pollicis arises with both oblique and transverse heads. The transverse head arises from the ulnar surface of the third metacarpal diaphysis and the oblique head from the base of the third metacarpal and flexor aspects of the trapezium, trapezoid, and capitate. The triangular muscle extends to insert at the base of the proximal phalanx of the thumb. This muscle serves to adduct the metacarpal and flex the MCP joint of the thumb (Table 11.3).⁴⁶^,⁵⁶

Table 11.3 Muscles of the Hand

Muscles	Origin	Insertion	Action	Innervations
Lumbricals (4)	Tendons of flexor digitorum profundus	Extensor aponeurosis	Extensors of interphalangeal joints	Radial or first and second lumbricals – median nerve, third and fourth ulnar nerve
Flexor pollicis longus	Anterior middle one-third radius and interosseous membrane	Distal phalanx thumb	Flexor of thumb	Median nerve (anterior interosseous branch)
Interossei palmar (3)	2,4,5 metacarpal diaphysis	Extensor aponeurosis	Abduction and adduction of fingers	Deep branch of ulnar nerve
Dorsal (4)	First to fifth metacarpal diaphysis	Proximal phalanges
Abductor pollicis brevis	Flexor retinaculum, trapezium	Radial side proximal phalanx thumb	Abductor of thumb	Median nerve
Flexor pollicis brevis	Flexor retinaculum, trapezium, and trapezoid	Radial flexor aspect proximal phalanx thumb	Flexes and rotates thumb	Median nerve
Opponens pollicis	Flexor retinaculum, trapezium	Radial diaphysis first metacarpal	Stabilize and opposition of thumb	Median nerve
Adductor pollicis	Third metacarpal, trapezium, trapezoid, capitate	Base proximal phalanx thumb		Median nerve
Palmaris brevis	Palmar aponeurosis (ulnar side)	Medial skin palm	Draws skin laterally	Deep branch ulnar nerve
Abductor digiti minimi	Pisiform	Ulnar base fifth proximal phalanx	Abductor fifth finger	Deep branch ulnar nerve
Flexor digiti minimi brevis	Hamate hook, flexor retinaculum	Ulnar base fifth proximal phalanx	Flexor fifth metacarpophalangeal (MCP) joint	Deep branch ulnar nerve
Opponens digiti minimi	Flexor retinaculum, distal hamate hook	Fifth metacarpal diaphysis	Draws fifth metacarpal anteriorly	Deep branch ulnar nerve
From Berquist TH. Magnetic resonance imaging of the elbow and wrists. Top Magn Reson Imaging. 1989;1:15-27; Rosse C, Rosse PC. Hollinshead’s Textbook of Anatomy. Philadelphia, PA: Lippincott-Raven; 1997 and Bishop AT, Gabel G, Carmichael SW. Flexor carpi radialis tendinitis. Part I: operative anatomy. J Bone Joint Surg Am. 1994;76A:1009-1014.

The hypothenar muscle group consists of one superficial and three deep muscles. The superficial muscle is the palmaris brevis that arises from the ulnar side of the palmar aponeurosis and extends medially to attach into the skin along the medial border of the palm. This muscle is superficial to the ulnar nerve and artery.⁵⁶ The deep muscles include the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi (Figs. 11.17 and 11.18). The abductor digiti minimi is the most superficial of the three deep muscles. It arises from the distal surface of the pisiform and passes distally along the medial aspect of
the hand to insert along the ulnar side of the base of the fifth proximal phalanx. This muscle abducts the little finger at the MCP joint. It acts along with the dorsal interosseous muscle to assist in abduction or spreading of the fingers. The flexor digiti minimi brevis arises more distally than the abductor digiti minimi and takes its origin from the hook of the hamate and flexor retinaculum. Thismuscle passes more obliquely and medially and inserts in the same position as the abductor. The main function of this muscle is as flexor of the fifth MCP joint. The third and final muscle of the deep hypothenar group is the opponens digiti minimi. This muscle is the deepest and arises deep to the abductor and flexor from the flexor retinaculum and distal hook of the hamate, taking an oblique course to insert along the ulnar aspect of the fifth metacarpal diaphysis. This muscle draws the fifth metacarpal anteriorly. All of the hypothenar muscle groups is innervated by the deep branch of the ulnar nerve (Table 11.3).⁴⁶^,⁵⁶

Figure 11.27 Flexor and extensor muscle groups.

Numerous muscular variations have been described.⁸¹^,⁸²

The accessory abduction digit minimi has been reported in up to 24% of patients. The extensor digitorum manus muscle is reported in 1% to 3% of the general population. The origin of the lumbrical muscles (Table 11.3) may vary, with the origin arising in the carpal tunnel in 22% of patients. The palmaris longus is typically seen only as a tendon at the level of the wrist. In up to 13% of patients, the muscle may be absent. There are numerous other variations, including palmaris longus inversus (muscle distally, tendon proximally), non-tendinous variation (muscle from origin to insertion), central tendon with muscle tissue proximally and distally, and a bifid variant with two tendinous insertions distally.⁵⁶^,⁸² A more complete discussion of muscle variants and clinical implications is included in the Pitfalls section of this chapter.

Neurovascular Anatomy

The neurovascular anatomy of the hand and wrist is complex (Fig. 11.28). Because there are numerous causes of nerve compression in this region, it is especially essential to understand the anatomy and relationship of these structures in the hand and wrist (Figs. 11.28 and 11.29).⁵⁴^,⁵⁵^,⁵⁶^,⁸³^,⁸⁴^,⁸⁵^,⁸⁶^,⁸⁷^,⁸⁸ MR evaluation of neurovascular anatomy is most easily accomplished by following these structures from proximal to distal on axial images (Figs. 11.17 and 11.29). On the ulnar side of the distal forearm proximal to the carpal tunnel, the ulnar artery, nerve, and the accompanying veins lie deep to the flexor carpi ulnaris (Fig. 11.17).⁵⁴^,⁵⁶ The nerve is generally medial to the artery at this level. At the level of the pisiform, these structures pass along the lateral or radial side of the pisiform, passing deep to the volar carpal ligament and then distally into the palm of the hand anterior to the flexor retinaculum but deep to the palmaris brevis muscle (Fig. 11.29B).⁸³ At the level of the pisiform, the ulnar nerve typically divides into superficial and deep branches (Fig. 11.29B). Also, at
the pisiform level, the nerve and accompanying vascular structures lie between the volar carpal ligament and flexor retinaculum in a space commonly known as the Guyon’s canal.⁵⁴^,⁵⁶ Lesions proximal to or within the canal can produce both sensory and motor abnormalities in the ulnar nerve distribution.⁵⁴^,⁵⁶

Figure 11.28 Vascular (A) and neurovascular (B) anatomy of the hand and wrist.

The two flexor digitorum muscles (superficial and profundus) are lateral to the ulnar nerve and vessels at the level of the wrist (Fig. 11.29). The tendon of the palmaris longus lies superficially. These structures are most easily identified on axial MR images (Figs. 11.17 and 11.29). The midline volar structures of the wrist, as they enter the carpal tunnel, tend to form three layers. The most superficial or anterior layer is formed by the flexor digitorum superficialis. The middle layer is formed by the superficial flexor of the index and middle fingers, and the most posterior or deepest layer is formed by the flexor digitorum profundus tendons. All tendons have a common sheath just before they pass under the flexor retinaculum. The palmaris longus tendon is the most superficial and midline structure at the wrist level (Figs. 11.17 and 11.29).⁴⁶^,⁵⁶

The median nerve lies deep to the flexor digitorum superficialis through much of the forearm (Figs. 11.17 and 11.29). Just proximal to the wrist, it emerges on the radial side of the superficial flexor and passes forward and medially to lie in front of the flexor tendons in the carpal tunnel (Figs. 11.17 and 11.29). At the distal margin of the flexor retinaculum, the median nerve divides into five or six branches. These small branches are difficult to identify, even when thin axial MR sections are obtained.²¹^,⁵⁵^,⁸⁸

Figure 11.29 Axial MRI demonstrating the relationships of the ulnar and median nerves at the level of the distal radioulnar joint (A), pisiform (B), and hamate hook (C).

The muscle planes and fascial compartments of the palm basically divide the palm into three compartments – the thenar, hypothenar, and central compartments (Figs. 11.17 and 11.28). These compartments, along with the tendon sheaths of the flexor tendons, are anatomically important in the spread of inflammatory and infectious diseases.⁵⁶

PITFALLS

Pitfalls of MRI of the hand and wrist may be due to anatomic variants, improper techniques, and software and hardware artifacts. Patient motion, flow artifacts, and other technical errors can lead to suboptimal images (Fig. 11.30).

Flow artifacts vary with different pulse sequences. Though they can occur in any anatomic location, they are more common in the peripheral extremities due to the number of vessels included in the tissue volume studied (Fig. 11.31). When flow artifacts enter the area of interest, lesions – especially small lesions – can be overlooked. In this setting, images can be repeated with changes in the phase direction that will direct the artifact out of the area of interest. Flow-suppression techniques are also useful for reducing artifacts.²¹

The magic angle phenomenon may cause increased signal intensity in tendons or ligaments oriented 45° to 65° to the magnetic field (B₀).⁸⁹ The direction of B₀ varies with the type of magnet. It is aligned with the bore in closed high field systems, vertical in open systems, and left to right in small extremity units. Proper positioning or use of radial or ulnar deviation of the wrist may reduce this phenomenon (Fig. 11.32).

Magic angle occurs with short TE spin-echo and many GRE sequences, but it is not a problem with long TE or T2-weighted sequences.²^,²¹^,⁸⁹ Abnormal signal intensity not related to magic angle phenomenon has been described in the ECU tendon.⁹⁰ However, pathology is unlikely in the absence of tendon enlargement or fluid in the tendon sheath.²^,²¹

Anatomic variants may involve osseous or soft tissue structures.⁹¹^,⁹²^,⁹³^,⁹⁴^,⁹⁵^,⁹⁶

Osseous Variants

The carpal bones generally develop from a single ossification center. Therefore, anomalous conditions such as bipartite and tripartite carpal bones are not common.⁶²^,⁶³ Unfortunately, when bipartite and tripartite carpal bones
do occur, they involve the most commonly fractured carpal bone, the scaphoid.⁵⁶^,⁶² The most common appearance is two separate ossicles separated at the waist, a common site of scaphoid fractures. The capitate and hook of the hamate may also develop from multiple ossification centers. When this occurs, differentiation from fracture may be difficult with MRI.⁶³ Hypoplastic hamate hooks have been described in females.⁶³^,⁹⁷

Figure 11.30 Axial T1- (A) and T2-weighted (B) images. The large vitamin E capsule compresses and distorts the underlying anatomy and ganglion cyst (arrow).

Osseous coalitions may be fibrous, cartilaginous, or osseous with an overall prevalence of 0.1%.⁹⁶ Lunotriquetral coalitions are most common, but capitohamate coalitions also occur (Fig. 11.33).⁶²^,⁶³^,⁶⁴^,⁹⁶ Coalitions are more common in females and African-Americans, occurring in up to 6% of the black population.⁵⁶^,⁶² Minaar classified lunotriquetral coalitions. Type I coalitions (Fig. 11.34A) are fibrous or cartilaginous and may be painful. Type II coalitions are incomplete osseous coalitions with a distal notch (Fig. 11.34B), and type III show complete osseous fusion (Fig. 11.34C). Type IV coalitions (Fig. 11.34D) are complete osseous fusions with other carpal anomalies.⁵⁶^,⁶⁴

As noted in the anatomy section, the lunate may have one distal facet (type 1) or two facets, one for articulation with the hamate (type 2) (Fig. 11.16). The type 2 lunate is more common (50% to 65%) and is associated with cartilage damage on the proximal pole of the hamate.⁶⁴ Pfirrmann et al.⁹⁸ found no correlation with interosseous and TFC tears.

Irregularity of the palmar aspect of the lunate may be seen on sagittal T1-weighted MRI. This is due to nutrient vessels and ligament attachments (Fig. 11.35).⁶²^,⁹⁹

There are numerous ossicles in the hand and wrist (Fig. 11.36). Common ossicles and their locations may be most easily appreciated on radiographs (Fig. 11.37). They should not be confused with loose bodies or fractures. The lunula (Table 11.4) is an ossification center that lies between the triangular fibrocartilage and the triquetrum. In some cases, it may fuse to the ulnar styloid (Fig. 11.36).⁶² The os styloideum, also known as a carpal boss, lies dorsal to the second and third metacarpal bases. This ossicle may be congenital or degenerative and may mimic a ganglion cyst clinically.⁶²^,⁶⁴ The os triangulare (Table 11.4) is congenital and lies in the ulnar fovea. The trapezium secondarium lies at the superomedial border of the trapezium (Fig. 11.37).⁶²^,⁶⁴ The epilunate lies dorsal to the lunate and is easily mistaken for a loose body because of its location.⁹⁰ The os hamuli lies at the tip of the hamate hook, and the os
Gruber-Ossiculum lies between the capitate, hamate, and the third and fourth metacarpal bases.⁶²^,⁶⁴

Figure 11.31 Axial 1.5 T T1-weighted (A) and T2-weighted (B) images demonstrating flow artifact (arrows) in the anteroposterior direction. The artifact is much more significant on the T2-weighted image (B). Axial 3.0 T T1-weighted (C) and T2-weighted (D) images demonstrating a change in phase direction with the artifact in the transverse direction. Again the artifact is slightly greater on the T2-weighted image. Phase direction can be swapped depending on the location of the lesion to avoid distortion of lesions from flow artifact.

Soft Tissue Variants

Soft tissue variants are common. Neurovascular variations in the dorsal and palmar arches may be noted in up to one-third of patients.⁵⁶ Lindley and Kleinert¹⁰⁰ evaluated the carpal tunnel in 526 elective surgical cases and noted anatomic variants in 6% of cases. Variations were most common in the median and ulnar nerves and persistence of the median artery. A persistent median artery occurs in 2% to 4% of the general population. This is usually asymptomatic, though if thrombosed, the vessel may cause median nerve compression (Fig. 11.38).⁹⁶

Variations in the position of the median nerve in the carpal tunnel may be evident due to position changes in the wrist during the examination. More proximal bifurcation or a bifid median nerve has also been described. This variation has been described in 3% of patients.¹⁰¹

Anomalous muscles may cause problems clinically as patients present with soft tissue masses or asymmetry when compared with the opposite extremity (Table 11.5).¹⁰²^,¹⁰³ The exact variation may not be apparent on MRI. However, the demonstration of a muscle density structure is obvious on MRI. Thus, a neoplasm can be excluded. Anomalous muscles have also been described in Guyon’s canal in 25% of patients. Anomalies are bilateral in 67%. Anomalous muscles can result in nerve compression syndrome.⁵⁵^,⁸²
Muscle anomalies most commonly involve the abductor digiti minimi, palmaris longus, flexor carpi ulnaris, and flexor digitorum superficialis.⁹⁶ Muscle anomalies are most often incidentally noted and do not cause symptoms.⁶²^,⁹⁶

Figure 11.32 Coronal SE 500/10 image of the flexor tendons. Most tendons are oriented in the plane of this closed high field magnet (B₀). The flexor pollicis longus is oriented 42° to B₀. Magic angle phenomenon could come into play depending upon the degree of radial or ulnar deviation of the wrist.

Figure 11.33 Lunotriquetral coalitions. A: Coronal T2-weighted image demonstrates a fibrous (type I) coalition. Note the low signal intensity and decreased joint space (arrow). The space is normal between the scaphoid and lunate and there is fluid in the joint space (open arrow). B: Coronal T1-weighted image demonstrating an osseous coalition with a proximal notch (arrow). T, triquetrum; L, lunate.

Table 11.4 Common Ossicles of the Hand and Wrist

Ossicle	Location
Lunula	Between triangular fibrocartilage complex and triquetrum, may fuse to ulnar styloid
Os styloideum	Dorsal to second and third metacarpal bases
Os triangulare	Distal to fovea
Trapezium secondarium	Superomedial aspect of trapezium
Epilunate	Dorsal to lunate
Os hamuli	Adjacent to hamate hook
Os Gruber	Between capitate, hamate, and third and fourth metacarpal bases
From references 62,63,64,65, 97, 99.

The accessory abductor digiti minimi is a common variant reported in 24% of the general population (Fig. 11.39). This muscle may originate from the palmar carpal ligament, palmaris longus, or forearm fascia. It inserts on the medial
aspect of the fifth proximal phalanx. Ulnar and median nerve symptoms have been associated with this anomaly (Fig. 11.39B).⁵⁶^,⁸²^,⁹⁶

Figure 11.34 Lunotriquetral coalitions. A: Type I, fibrous or cartilaginous. B: Type II, incomplete osseous coalition with a distal notch. C: Type III, complete osseous fusion. D: Type IV, complete osseous fusion with other carpal anomalies, in this case a bipartite scaphoid. (From Berquist TH. MRI of the Hand and Wrist. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.)

The extensor digitorum brevis manus muscle occurs in 1% to 3% of patients. This muscle arises from the distal radius or radiocarpal ligament and inserts on the distal second metacarpal (Fig. 11.40).⁸²^,⁹⁰^,⁹¹^,¹⁰⁴ This muscle is generally not symptomatic, but it may mimic a ganglion cyst.⁹¹

In 22% of patients, the lumbrical muscles may have a more proximal origin in the carpal tunnel. Nerve compression may occur with finger flexion.⁹¹^,⁹⁶

The palmaris longus typically takes its origin from the medial epicondyle. There are numerous variants (Fig. 11.41), and the muscle is absent in 13% of the population.⁸²^,¹⁰⁵^,¹⁰⁶

Variations in the flexor tendon sheaths are more significant. Anomalies may lead to changes in patterns of spread of
infection. Also, confusion of tenosynovitis with a ganglion can occur. Most often, the common flexor tendon sheath ends in the mid palm (71.4% of the population). The digital sheaths in the fingers do not usually communicate with the common flexor tendon sheath.⁵⁶

Figure 11.35 Sagittal T1-weighted image demonstrating volar irregularity of the lunate (arrow) due to normal ligament attachments.

As noted above (Figs. 11.22, 11.23, 11.24), variations in shape and signal intensity of the ligaments and TFC complex may also cause confusion.¹⁰⁷^,¹⁰⁸ The ulnar aspect of the TFC is rich in vascular tissue that can result in increased signal intensity (Fig. 11.42). These changes should not be confused with a tear.⁷³^,⁸² Variations in signal intensity, as with arthrography, need to be correlated with clinical symptoms. In some cases, arthrography with diagnostic injection may be necessary to confirm MR findings and localize the patient’s symptoms. Also, similar to the meniscus in the knee, signal changes in the TFC have also been described with aging.¹⁰⁹^,¹¹⁰

Table 11.5 Muscle Variants of the Hand and Wrist

Muscle	Incidence	Clinical Significance
Accessory abductor digiti minimi	24%	Usually none, may compress ulnar or median nerve
Extensor digitorum brevis manus muscle	1%-3%	None, may mimic a ganglion
Lumbrical origin anomaly	22%	Mimics carpal tunnel pathology
Palmaris longus	13% absent multiple variants	May mimic soft tissue mass or muscle tear, nerve compression
Accessory flexor digitorum superficialis	–	Mimics soft tissue mass
Flexor digiti minimi (anomalous origin)	–	Ulnar nerve compression
From references 82, 90, 91, 106.

Figure 11.36 Coronal gradient-echo image demonstrating an elongated ulnar styloid with faint signal intensity increase (arrow) due to a partially fused lunula.

With aging the incidence of central asymptomatic defects in the TFC increases.⁹⁶^,¹¹¹ Zanetti et al.¹¹¹ found communications in the TFC in 56 patients and 64% were asymptomatic. The defects were bilateral in 69% of the patients and most occurred at the radial aspect of the TFC. Defects near the ulnar attachment of the TFC were more often symptomatic.¹¹¹

CLINICAL APPLICATIONS

Clinical applications for MRI of the hand and wrist have expanded dramatically due to improved surface coil technology, new pulse sequences, and increased utilization of MR arthrography and MR angiography.¹⁰^,¹¹²^,¹¹³^,¹¹⁴^,¹¹⁵^,¹¹⁶^,¹¹⁷ Major applications for MRI in our practice include trauma, neoplasms, infection, osteonecrosis, nerve compression syndromes, and arthropathies. MRI may also be of value
in imaging other conditions in the hand and wrist. However, experience is still evolving in these areas.²⁷^,⁴³^,¹¹⁸^,¹¹⁹^,¹²⁰

Figure 11.37 Ossicles of the wrist seen from dorsal (A), volar (B), and sagittal (C). Coronal T1-weighted image (D) demonstrates an os centrale (arrowhead). (From Berquist TH. MRI of the Hand and Wrist. Philadelphia, PA: Lippincott Williams & Wilkins; 2003.)

Figure 11.38 Axial T1-weighted (A) and post-contrast fat-suppressed T1-weighted (B) images demonstrating a persistent median artery (arrow).

Figure 11.39 A: Accessory abductor digiti minimi. B: Axial MR image demonstrating the relationships of the muscle to Guyon’s canal. Normally, there is no muscle in this region.

Figure 11.40 A: Extensor digitorum manus. B: Axial MR image demonstrating the location at the level of the metacarpal bases. The muscle is radial to the extensor tendons and between the second and third metacarpals.

Figure 11.41 Palmaris longus muscle variations. A: Normal; B: inverse variant; C: total muscle variant; D: proximal and distal bellies. E: Axial MR image demonstrating the location of the palmaris longus inversus variant B at the radiocarpal joint. Note the relationship to the median nerve.

TRAUMA

Osseous Injuries

MRI techniques are useful to evaluate acute and chronic musculoskeletal injuries to the hand and wrist.²¹^,⁵¹^,¹¹⁹^,¹²¹^,¹²²^,¹²³ Most acute skeletal injuries are adequately diagnosed with routine radiography. CT is a valuable and commonly used technique for evaluation of subtle fractures, complex fractures, and for operative planning purposes.⁷^,¹²⁴^,¹²⁵^,¹²⁶

MRI is useful for early diagnosis of subtle injuries and to evaluate the extent of osseous, physeal, and soft tissue injuries in more complex cases.²¹^,¹²⁷^,¹²⁸^,¹²⁹^,¹³⁰^,¹³¹ Osseous injuries
include incomplete fractures, complete fractures, physeal fractures, stress fractures, and bone bruises.²¹^,¹²⁸^,¹³⁰^,¹³²^,¹³³

Figure 11.42 Coronal DESS images at 1.5 T (A) and 3.0 T (B) demonstrating intermediate to increased signal near the ulnar attachment of the triangular fibrocartilage in normal asymptomatic patients.

Early diagnosis of fractures, especially of the scaphoid, is essential to reduce complications. MRI should be considered when radiographs or computed radiography (CR) images are normal, but fracture is suspected clinically. Up to 35% of fractures detected on MRI cannot be identified on radiographs.¹³³

Fractures of the distal radius and ulna are common (Fig. 11.43). MRI may be particularly useful in children. Forty percent of physeal injuries in children involve the distal radius and 5% involve the ulna.¹³⁴ Physeal fractures and soft tissue injuries are included in the spectrum of gymnast’s wrist.¹³⁵^,¹³⁶^,¹³⁷ High loads applied to the wrist during gymnastics commonly result in injury, especially between the ages of 12 and 14 years.¹³⁵ Radiographs may demonstrate irregularity and cystic changes in the physis. Ulnar positive variance has also been described with this condition.¹³⁵^,¹³⁷

Figure 11.43 Distal radial fracture. Coronal T1- (A) and sagittal DESS (B) images demonstrate an undisplaced distal radial fracture (arrows) with marrow edema.

Carpal fractures are rare in children, but common in adults.¹³⁴^,¹³⁸ The scaphoid is the most commonly fractured
carpal bone in adults and children. However, in children, scaphoid fractures account for only 2.9% of hand and wrist fractures. In adults, scaphoid fractures most commonly involve the waist, while in children the distal third is the most common fracture site (Fig. 11.44).¹³⁴^,¹³⁸ Fractures of the triquetrum are the second most common carpal fracture followed by the capitate (Fig. 11.45) and lunate (Fig. 11.46).⁷^,¹³⁴

Figure 11.44 Scaphoid fracture. Coronal T1- (A) and DESS (B) images demonstrating a scaphoid waist fracture (arrow).

MRI is sensitive and specific for early detection of fractures, including bone bruises (Fig. 11.47).¹³⁹ Imaging approaches vary depending upon the site of injury. Specifically, different image planes may be required to fully evaluate each carpal bone (Table 11.6). Both T1- and T2-weighted sequences are obtained. In some cases, STIR or fast inversion recovery are added to the examination. Marrow edema is low signal intensity on T1-weighted and high signal intensity on T2-weighted or STIR sequences. Signal intensity is low along the fracture line on both T1- and T2-weighted sequences with trabecular compression or impaction (Figs. 11.44 and 11.45). Increased signal intensity is seen in the fracture line on T2-weighted sequences when fragments are not impacted.²^,²¹ Image planes are especially
important for the scaphoid (Fig. 11.48). Sagittal image planes aligned with the scaphoid are important to exclude “hump back” deformity.⁷

Figure 11.45 Capitate fracture. Coronal T1- (A) and T2-weighted (B) images of a capitate fracture (arrow). The fracture line is low signal intensity on both sequences. Edema is more obvious on the T2-weighted sequence.

Figure 11.46 Lunate fracture. Sagittal gradient-echo (A) and fat-suppressed proton density (B) images demonstrate a lunate fracture (arrow). Fracture lines are usually most obvious in the sagittal plane.