Imaging of the Hand and Wrist

Key points

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Radiographs are the primary initial diagnostic tool for hand and wrist injuries, particularly in the setting of osseous injury.
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Computed tomography offers improved contrast resolution compared with radiographs and the benefit of multiplanar reconstruction and is particularly useful in the setting of suspected osseous injuries with negative or equivocal radiographs.
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Magnetic resonance imaging and magnetic resonance arthrogram are the modalities of choice for evaluating soft tissue injuries of the hand and wrist and occult fractures.
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Ultrasound provides good visualization of superficial structures, such as tendons, peripheral nerves, the digital pulley system, and ganglion cysts. Ultrasound excels in the ability to dynamically evaluate structures and to compare with the contralateral anatomy.

Introduction

Hand and wrist injuries are common in athletes, accounting for 9% to 25% of sports injuries. ^, The hand and wrist anatomy is complex and often requires the evaluation of small structures that have significant implications on clinical and surgical management. Conventional radiographs, computed tomography (CT), magnetic resonance imaging (MRI), MR arthrography, and ultrasound are all commonly used in the evaluation of hand and wrist injuries. This article reviews strengths and limitations of these imaging modalities and how they can best be utilized in commonly encountered clinical questions.

Imaging modalities

Conventional Radiographs

Osseous injuries of the hand and wrist often are diagnosed based on a combination of clinical examination and plain radiographs. Even with the availability of advanced imaging modalities, conventional radiographs remain cost effective, offering a large amount of information to help guide further evaluation and treatment. Initial radiographs should consist of 3 views of the affected area: posteroanterior (PA), oblique, and lateral, although specialized views also may be requested.

Conventional radiographs of the hand and wrist are best evaluated with an organized approach. All radiographic interpretations should first include an evaluation of positioning and technique. Positioning in patients with an acute injury and pain may be challenging, and it is important to ensure that the radiographs are adequate to answer the clinical question. Particular attention should be paid to osseous alignment. This is important in the evaluation of acute injuries to identify not only dislocations but also more subtle alignment abnormalities that may indicate a soft tissue injury. It also is important to identify old osseous injuries, anatomic variants, and accessory ossicles that may confound the interpretation of radiographs in an acute injury ( Fig. 1 ).

In the setting of a suspected acute hand or wrist fracture, radiographic examination is the initial test of choice. ^, Radiographs also remain the primary modality for fracture follow-up to confirm healing. Due to overlapping structures and lack of dedicated views in some cases, some fractures of the hand and wrist are not well seen radiographically. Fractures of the lunate, triquetrum, capitate, and hamate are particularly challenging to diagnose on radiographs. Conventional radiographs also have low sensitivity in the detection of early stress fractures.

Digital radiography offers the benefit of improved dynamic range over conventional radiographs with better visualization of the soft tissues. Radiographs of the hand and wrist should be evaluated carefully for areas of soft tissue swelling or abnormalities that may suggest a soft tissue injury better evaluated with advanced imaging ( Fig. 2 ).

Computed Tomography

CT of the hand and wrist should be obtained using thin slices (<1 mm) with isometric voxels that subsequently can be reformatted in any plane. This also allows for the creation of 3-dimensional (3-D) reformatted images and 3-D printed models for operative planning. Although 3-D printed models are not routinely used in clinical practice, they are a tool that likely will become more available in the future and may be beneficial in the treatment of complex injuries, such as scaphoid malunion.

Noncontrast CT often is indicated in the evaluation of suspected hand or wrist fractures with negative or equivocal radiographs, but the cost benefit of the exposure to ionizing radiation and added cost should be considered. CT also can be used for further characterization of known fractures, to aid in preoperative planning, and to evaluate fracture healing not well depicted on conventional radiographs. ^, ^, ^, Displacement of fracture fragments, comminution, intra-articular extension, and articular surface step-off and gap are better demonstrated on CT than conventional radiographs ( Fig. 3 ).

The superior contrast resolution of CT compared with conventional radiographs also allows for gross evaluation of the surrounding soft tissues, including the tendons of the wrist. As with conventional radiographs, it is important to evaluate the soft tissues because injuries sometimes are identified ( Fig. 4 ).

CT arthrography has been shown to be at least as accurate as MR arthrography in the diagnosis of intrinsic ligament and triangular fibrocartilage complex (TFCC) tears, although it is relatively limited in the evaluation of bone marrow and other extra-articular structures. CT arthrography may be useful for ligamentous evaluation in patients with contraindication to MRI.

Dynamic (4-dimensional) CT allows for noninvasive assessment of osseous alignment during wrist motion and may guide surgical treatment in situations, such as scapholunate ligament (SLL) and distal radioulnar joint (DRUJ) instability. ^,

Dual-energy CT (DECT) is performed by obtaining images at 2 different energy levels. Musculoskeletal applications for DECT include creating virtual noncalcium images, reducing metal artifact, creating iodine maps in contrast-enhanced studies, identifying monosodium urate deposition in gout, and assessing tendons. Virtual noncalcium images are created by subtracting calcium from cancellous bone, allowing for the identification of bone marrow lesions, such as edema, which can aid in the diagnosis of acute fracture. DECT techniques that reduce beam hardening artifact from metal allow improved visualization of tissues surrounding prostheses and hardware.

Cone beam CT is a technique available on certain x-ray units that provides similar information to standard CT technique ( Fig. 5 ). In the hand and wrist, cone beam CT offers the benefit of superior accuracy in the detection of carpal region fractures compared with standard radiographs, with lower radiation dose than conventional CT. Additionally, positioning is easier compared with the traditional superman position, which may be difficult in a patient with concomitant shoulder injury. Cone beam CT may serve as an alternative to conventional CT for the evaluation of acute osseous injury as well as follow-up of fracture healing that is not well depicted on conventional radiographs.

Magnetic Resonance Imaging

The superior contrast resolution of MRI makes it the modality of choice for evaluation of suspected soft tissue injuries in the hand and wrist. ^, Subtle bony abnormalities, such as occult fracture, osteonecrosis, and abutment syndromes, also are best evaluated by MRI. MRI also can play an important role in the assessment of arthritis and articular cartilage.

Given the intricate anatomy of the wrist, it is critical to obtain images with high spatial resolution, high-contrast resolution, and high signal-to-noise ratio. ^, A dedicated coil, small field of view, and thin contiguous slices are important technical considerations. 3T MRI, has been shown to provide significant diagnostic benefit relative to 1.5T MRI. ^, ^, T1-weighted (T1), T2-weighted fat-saturated (T2FS), proton density (PD), and gradient sequences are the sequences typically used for the evaluation of wrist and hand injuries. A combination of these sequences is used to evaluate for a wide possibility of pathologic processes. Isotropic 3-D MRI may be considered to allow for the reformatting of images into any plane, which may help in visualizing anatomy that runs oblique to the standard axial, sagittal, and coronal orientations.

MRI is ideal in the setting of occult wrist fractures due to its ability to image both cortex and bone marrow. ^, On MRI, an acute fracture is identified as a low-signal intensity line extending through the bone on all sequences with surrounding bone marrow edema ( Fig. 6 ). ^, Bone contusion is seen as areas of bone marrow edema (high signal within the marrow on fluid-sensitive sequences) without a discrete fracture line. ^, At least 1 plane of T1-weighted images without fat saturation is recommended in all wrist and hand MRI examinations because it provides the best depiction of a fracture and helps differentiate nondisplaced fractures from bone marrow contusions.

Magnetic Resonance Arthrography

Direct MR arthrography is a minimally invasive technique that provides higher sensitivity in the detection of scapholunate and lunotriquetral ligament and TFCC injuries than conventional MRI ( Fig. 7 ). ^,

It is critical for radiologists performing the contrast injection to have an understanding of the clinical question because the compartments injected and order of injection may be altered to better answer the specific clinical question. Triple-compartment arthrography refers to the injection of 3 compartments of the wrist under fluoroscopic guidance prior to MRI (midcarpal, radiocarpal, and distal radioulnar). Depending on the clinical question, any number of the 3 compartments can be injected and all 3 might not be required for the diagnosis. The findings at injection under fluoroscopy can be particularly helpful in the diagnosis and are an important portion of the entire examination.

On MR arthrography, a complete ligamentous tear is seen when there is disruption of the ligament and communication of contrast between the radiocarpal and midcarpal joints. Fluid within a small ligamentous defect, but no communication between these joints, indicates a partial tear.

Ultrasound

Ultrasound is a useful tool in the evaluation of hand and wrist pathologies, particularly given its dynamic nature, ability to compare with the contralateral side, relative accessibility, relatively low cost, and lack of ionizing radiation.

Use of a high-resolution linear array transducer with a broad bandwidth is recommended for musculoskeletal applications. A high-frequency transducer (10–15 MHz) should be used for the evaluation of superficial structures. Color and power Doppler imaging allow for the assessment of vascularity, which may be increased in the setting of tenosynovitis or injury.

The tendons, digital pulley system, and peripheral nerves of the hand and wrist can be well assessed sonographically. ^, Some superficial ligamentous injuries also can be identified, and the ability to stress the joint under direct visualization can provide information regarding the severity of the injury. Ultrasound is a useful tool for the evaluation of soft tissue masses, such as ganglion cysts, or in the identification of radiolucent foreign bodies. In the setting of inflammatory or osteoarthritis, ultrasound also be can used to detect synovitis, joint space narrowing, erosions, and/or joint effusions.

When intervention, such as aspiration or injection, is indicated, ultrasound can safely guide these procedures.

Limitations of ultrasound are the difficulty in imaging intrinsic structures of the wrist, such as the TFCC and intrinsic ligaments, and the inability to visualize subtle bony pathology. ^,

Commonly encountered pathologies in the athlete’s hand and wrist

Distal Radial and Ulnar Fractures

Standard PA, oblique, and lateral views are necessary for complete assessment of distal radial fractures and for detecting associated fractures. ^, One study found that the semisupinated oblique view of the wrist was the most sensitive radiographic view for the detection of radial fractures, possibly because it displays the dorsal cortex most clearly ( Fig. 8 ). Key features to assess radiographically include the degree of displacement, degree of comminution, extension into the distal radioulnar and/or radiocarpal joints, radial length, inclination, tilt, and the presence of associated injuries. CT may provide better detail of the fracture and aid in treatment planning. MRI is useful if there is suspicion for associated soft tissue injury or in the setting of suspected radiographically occult fracture.

Fractures of the ulnar styloid are readily diagnosed on PA radiographs of the wrist. Both size and degree of displacement of the ulnar styloid fracture are risk factures for DRUJ instability.

Carpal Fractures

The scaphoid is the most commonly fractured carpal bone, representing approximately 70% of carpal fractures. ^, ^, ^, Initial radiographs should include PA and lateral radiographs of the wrist in neutral, an oblique view at 45° to 60° pronation, and a PA view with the wrist in 45° ulnar deviation and pronation. ^, Because approximately 20% of scaphoid fractures are occult on initial radiographs, either repeat radiographs in 10 days to 14 days or CT or MRI should be obtained if there is clinical suspicion. ^, CT may be used to better assess the 3-D anatomy of the fracture, evaluate displacement, and plan the operative approach. The sensitivity and specificity of MRI in the diagnosis of scaphoid fractures have both been reported at 100%. MRI has the added benefit of evaluating for associated soft tissue injuries concurrently. Stress fractures of the scaphoid are best diagnosed with MRI (see Fig. 6 ).

Lunate fractures account for approximately 1% of all carpal fractures. Small fractures may not be detected on plain radiographs due to overlapping bone; therefore, CT or MRI is indicated if the clinical examination is suggestive.

The triquetrum is the second most commonly fractured carpal bone, with the vast majority being dorsal chip fractures. Triquetral body fractures make up the majority of the remaining fractures and often are seen in high energy injuries. Triquetral fractures often can be diagnosed with PA, lateral, and 45° pronated oblique radiographs of the wrist; the lateral view is particularly useful for dorsal chip fractures (see Fig. 8 ).

Pisiform fractures are rare; however, they may be underestimated because they are challenging to diagnose on radiographs. ^, The semisupinated oblique view highlights the pisiform and pisotriquetral joint (see Fig. 5 ). Injury to the pisotriquetral joint is demonstrated by a joint width of greater than 3 mm or if the bone surfaces are more than 20° from parallel. The carpal tunnel view also may be useful to diagnose pisiform fractures (see Fig. 5 ).

Fractures of the trapezium occur most commonly in the body and typically are identified on standard views of the wrist. A pronated anteroposterior (AP) view, or Bett view, can be used to improve visualization of the trapeziometacarpal articulation. CT may be useful to identify more unusual fractures, such as occult trapezial ridge and coronal fractures.

Trapezoid fractures are rare, and most fractures and fracture dislocations should be diagnosed on standard views of the wrist. Dislocation of the trapezoid allows proximal migration of the second metacarpal, best identified on the PA view.

Capitate fractures also are typically well seen on standard views of the wrist. Fractures in the coronal plane, however, are more easily identified by CT scan.

Hook of the hamate fractures are the most common fractures of the distal carpal row ( Fig. 9 ). ^, Hamate fractures are challenging to diagnose on standard wrist radiographs due to overlapping bones but may be suspected when the hook is not well visualized on the PA view. ^, Specialized views, such as the carpal tunnel view or lateral view with the hand radially deviated and the thumb abducted, can aid in diagnosis. ^, CT has demonstrated sensitivity and specificity of 100% and 94%, respectively, and is considered the test of choice. ^, ^, MRI is indicated when there is suspicion of an associated ulnar nerve or tendinous injury.