Musculoskeletal ultrasound of the wrist

INTRODUCTION — The wrist and proximal hand are susceptible to a variety of injuries and conditions. Due to the relatively superficial location of many wrist and hand structures, many of these pathologic conditions can be diagnosed or assessed using ultrasound (US).

This topic will review a standard, systematic approach to musculoskeletal ultrasonography of the wrist and proximal hand. Topics devoted to conditions and injuries involving the wrist and hand pain are found separately. (See "Evaluation of the adult with subacute or chronic wrist pain" and "Evaluation of the adult with acute wrist pain" and "History and examination of the adult with hand pain".)

USES, ADVANTAGES, AND LIMITATIONS OF WRIST AND HAND ULTRASOUND — Musculoskeletal ultrasound (US) uses high frequency sound waves (1 to 20 megahertz, MHz) to produce high-resolution images of soft-tissue structures (eg, nerves, tendons, muscles, ligaments, bursae) and bony surfaces.

US has many advantages over other imaging modalities, including portability and point of care diagnosis [1]. Many of these general advantages are discussed separately. (See "Musculoskeletal ultrasound of the shoulder", section on 'Uses, advantages, and limitations of shoulder ultrasound'.)

For evaluation of the wrist and proximal hand in particular, US offers the ability to visualize small joints and articulations, and adjacent structures, both statically and dynamically (ie, visualize while the joint or articulation is manipulated) with resolution that is the equal of (or sometimes superior to) magnetic resonance imaging (MRI). Imaging of structures like the median nerve or the ulnar collateral ligament of the thumb can be performed in a number of ways from different perspectives, providing sufficient diagnostic accuracy to forego additional diagnostic testing. As an example, serial measurements of the circumferential volume of the median nerve obtained using short-axis US views can demonstrate areas of enlargement or compression, while long-axis views can confirm the appearance of the nerve and the site of compression. These measurements enable the clinician to diagnose carpal tunnel syndrome with an accuracy comparable to electrodiagnostic testing [2].

However, like all imaging modalities, US has limitations. For instance, sound waves do not penetrate bone, and therefore US cannot identify intramedullary lesions or evaluate pathology in tissues deep to bones or calcified tissues.

US enables focused imaging of a specific region. Therefore, it is most appropriate to use US when the patient's symptoms are relatively localized. If a patient presents with diffuse pain, they are often better served by an imaging modality that provides a larger field of view, such as standard radiographs, MRI, or computed tomography (CT).

The quality of the US image obtained depends upon the skill of the examiner and the quality of the US equipment. For the wrist and hand, smaller specialized high frequency probes provide higher resolution images of smaller joints and structures. Consequently, it is important for the sonologist to recognize the limits of their skills and equipment when performing an examination.

WRIST AND HAND ANATOMY FOR ULTRASOUND EXAMINATION — In this section, the wrist and hand anatomy most pertinent to the ultrasound (US) examination is briefly reviewed. A more detailed discussion of wrist anatomy is provided separately. (See "Anatomy and basic biomechanics of the wrist".)

Orientation and terminology — The anatomic position of the wrist defines the palmar (or volar) surface as anterior and the dorsal surface as posterior (figure 1 and figure 2). The ulna is considered medial and the radius lateral. The wrist includes the distal aspect of the radius and ulna, the eight carpal bones, and the articulations of the carpal bones and the proximal metacarpals.

Structures that can be imaged

●Carpal and metacarpal bones – The carpal bones are divided into two rows: proximal and distal (image 1 and figure 3). The proximal carpal row is composed of the scaphoid, lunate, triquetrum, and pisiform. The distal carpal row is comprised of the trapezium, trapezoid, capitate, and hamate. The metacarpals are numbered by convention, with the thumb metacarpal being the first, the index finger metacarpal being the second, and so on.

US can be used to look for fractures and avulsion injuries of the wrist and hand. Using high resolution and a high frequency transducer, the cortex of the scaphoid can be scanned in long axis using the dorsal and palmar probe positions to evaluate for disruption of the cortex. The same approach can be used to look for fractures of the metacarpals and phalanges (image 2). US can be used to scan for avulsion fractures of the trapezium, hook of the hamate and phalanges (image 3).

●Wrist ligaments – The ligaments of the wrist form a complex network of collagen fascicles that almost completely cover the carpal bones (figure 4). It is important to examine the scapholunate ligament for signs of injury (image 4).

●Triangular fibrocartilage complex – The triangular fibrocartilage complex (TFCC) is formed by the triangular fibrocartilage, radioulnar ligaments, and ulnocarpal ligaments (UCL) (figure 5). The TFC can be seen in both long and short axes using US [3]. Identification of a hypoechoic defect suggests injury (image 5).

●Wrist tendons – There are no intrinsic muscles of the wrist. All have their origins proximal to the wrist joint and insert at the hand, predominantly onto the metacarpals (figure 6). An exception is the flexor carpi ulnaris, which inserts at the pisiform and fifth metacarpal base. The wrist tendons are best scanned in short axis.

●Extensor compartments – The extensor tendons are held in place by the extensor retinaculum (figure 6). As the wrist extensor muscles contract and these tendons move along the posterior aspect of the wrist, they are protected within synovial sheaths. Tendinopathies of the dorsal wrist are common and conditions such as de Quervain's tenosynovitis typically cause swollen tendons. In acute conditions, an effusion within the synovial sheath and surrounding the tendon is seen on US (image 6), whereas in chronic conditions the tendons may appear hypoechoic. Listers tubercle is an anatomical landmark that helps distinguish compartment 2 (where it is not seen) from compartment 3. Wrist masses can be evaluated for ganglion cysts and other pathology (image 7).

The extensor tendons that traverse the wrist are contained within six compartments:

•Compartment 1 – Contains the abductor pollicis longus and the extensor pollicis brevis tendons (image 8). These tendons lie within the radial border of the anatomical snuff box.

•Compartment 2 – Contains the extensor carpi radialis longus and extensor carpi radialis brevis tendons (image 9).

•Compartment 3 – Contains the extensor pollicis longus tendon, which passes medial to the dorsal tubercle (Lister's tubercle) of the radius (image 10). The extensor pollicis longus tendon attaches to the base of the distal phalanx of the thumb, forming the ulnar border of the anatomical snuff box (picture 1 and picture 2).

•Compartment 4 – Contains the extensor digitorum and extensor indicis tendons (image 11). Proximally, the four tendons of the extensor digitorum join the tendon of the extensor indicis to pass deep to the extensor retinaculum through the tendinous sheath of the extensor digitorum and extensor indicis. Then, on the dorsum of the hand, the tendons fan out as they run towards individual fingers.

•Compartment 5 – The extensor digiti minimi tendon travels through this compartment, posterior to the distal radioulnar joint (image 12).

•Compartment 6 – Contains the extensor carpi ulnaris tendon (image 13). It runs in a groove between the ulnar head and its styloid process.

Carpal tunnel — Nine flexor tendons and the median nerve pass through the carpal tunnel, which can be examined with US (figure 7 and figure 8 and image 14 and image 15 and image 16):

●Flexor digitorum profundus (four tendons) (figure 9)

●Flexor digitorum superficialis (four tendons) (figure 10 and figure 11)

●Flexor pollicis longus (one tendon)

The median nerve courses between tendons of flexor digitorum profundus and flexor digitorum superficialis. Changes to the shape, circumferential volume, and echotexture of the median nerve seen on US can help confirm the diagnosis of carpal tunnel syndrome (image 17 and image 18).

Guyon's canal — Also known as the "ulnar canal" or "ulnar tunnel," Guyon's canal is the space between the pisiform bone and the hamate bone through which the ulnar artery and the ulnar nerve travel into the hand (figure 12 and image 19). Although less common than nerve syndromes involving the carpal and cubital tunnels, compression of the ulnar nerve within Guyon's canal can develop, sometimes caused by pressure from a ganglion cyst.

On the ulnar aspect of the volar wrist, the superficial and deep branches of the ulnar nerve course in close proximity to the hamate bone. Repetitive pressure on this region (eg, cyclist gripping handlebars, manual laborers gripping tools) can injure these nerves. Thickening of the portion of the nerve that travels over the hook of the hamate may be visible on US.

Volar aspect of the fingers — The volar aspect of the fingers includes the flexor digitorum superficialis and profundus tendons. The flexor superficialis tendons split at the proximal interphalangeal joint and insert on the middle phalanx. The split allows the flexor digitorum profundus to continue its course and insert on the distal phalanx. US can be used to look for thickened nodules within the tendon sheath and thickened pulleys causing conditions such as trigger finger. (See "Trigger finger (stenosing flexor tenosynovitis)".)

Dorsal aspect of the fingers — The anatomy of the dorsal aspect of the fingers includes the extensor digitorum attaching to the middle phalanx as a central band and lateral slips of the extensor tendon attaching to the distal phalanx. US can be used to evaluate tendon avulsions such as mallet finger. (See "Extensor tendon injury of the distal interphalangeal joint (mallet finger)".)

Neurovascular anatomy — Three nerves – the ulnar (figure 13), median (figure 14), and superficial cutaneous branch of the radial nerve (figure 15) – cross the wrist joint (figure 16). The ulnar nerve is visible with US coursing along with the ulnar artery (figure 12 and figure 17 and figure 13 and image 19). The median nerve travels in the carpal tunnel with the flexor tendons (image 17).

The blood supply of the wrist and hand is provided by branches of the radial, ulnar artery, and interosseous arteries (figure 18 and figure 19 and figure 20). Doppler US is useful for evaluating blood flow. Keep in mind that veins can be difficult to see because the pressure of the transducer may cause them to collapse.

ULTRASOUND EXAMINATION OF THE WRIST AND HAND

Guidelines, structures to image, and positioning — The American Institute of Ultrasound in Medicine (AIUM) and European Society of Skeletal Radiology (ESSR) recommend performing a regional examination, as is the case with other joints with the exception of the shoulder, regardless of the pathology suspected [4-6].

A high frequency linear array transducer is preferred to a curvilinear transducer for examination of the wrist and hand because the transmitted ultrasound (US) beam is perpendicular to the transducer surface, resulting in less divergence of the US waves and better visualization of superficial structures.

While the examination is performed, the patient sits with their hands resting on a table placed anteriorly (picture 3) or on a pillow placed on the patient's thighs. Alternatively, the examination can be performed with the patient supine (picture 4). The volar examination requires the patient's wrists to be placed flat or in mild dorsiflexion with the palm up, including examination while the wrist is in ulnar or radial deviation, to allow visualization of all necessary structures. The dorsal scan requires the wrist to be placed palm down with mild volar flexion.

Volar wrist and hand-midline — Structures examined as part of the US assessment of the volar wrist include:

●Median nerve

●Flexor digitorum superficialis tendon

●Flexor digitorum profundus tendon

It is best to begin scanning in short axis relative to the tendons and median nerve because the structures are easier to identify from this perspective. To find the median nerve, the transducer is placed in a short axis at the proximal aspect of the carpal tunnel, identified at the wrist crease (image 15). Peripheral nerves are comprised of both hypoechoic and hyperechoic fascicles; the median nerve appears hypoechoic when surrounded by the hyperechoic tendons.

It can be challenging to distinguish the median nerve from the flexor tendons of the wrist. To do so, the sonographer can scan in short axis proximally and identify the median nerve as it courses deep between the flexor digitorum superficialis and profundus [7]. As you scan proximally in short axis, the transition from tendon to muscle becomes visible, and the median nerve appears hyperechoic relative to the muscle tissue.

Another method for identifying the median nerve is to toggle the transducer, which causes the hyperechoic tendons to become hypoechoic as a result of anisotropy, while the hypoechoic appearance of the median nerve fascicles remains unchanged.

The flexor digitorum superficialis and profundus are identified while examining the median nerve in short axis (image 17 and image 15). The flexor digitorum tendons course through the carpal tunnel and extend to the fingers. Examining the long axis of the flexor tendon is less useful than examining it in short axis, as the swelling of individual tendons and intratendinous breakdown are better demonstrated in short axis.

The volar radiocarpal and midcarpal joint recesses are identified by the adjacent bony contours in long axis. The joint and volar recesses are evaluated for anechoic fluid, synovial hypertrophy, and other signs of pathology.

Volar wrist and radial hand — Examination of the radial aspect of the volar wrist begins at the wrist crease, as when examining the median nerve. At the wrist crease, the flexor carpi radialis tendon is seen just radial to the median nerve, which is similar in size (image 15). This tendon is located outside the carpal tunnel and can be examined in both long and short axis from proximal to the distal insertion of the flexor carpi radialis tendon on the second and third metacarpals, with some fibers inserting onto the trapezium [8].

As the transducer is moved over the distal aspect of the flexor carpi radialis tendon in long axis, the scaphoid bone can be identified deep to the tendon. The hyperechoic peanut shaped bone surface of the scaphoid bone can be evaluated for cortical step-off, which suggests a fracture. If the sonographer places the transducer in a transverse orientation between the scaphoid and lunate, the hyperechoic scapholunate ligament can be seen. The radial artery and veins can be seen just radial to the flexor carpi radialis tendon.

Volar wrist and ulnar hand — The pisiform can be identified at the ulnar aspect of the volar wrist and used as a landmark for US examination. The ulnar nerve is seen between the pisiform and the ulnar artery (image 19). The ulnar veins are easily compressed by the pressure of the transducer but are not usually seen. As the sonographer scans distally, the hook of the hamate is seen deep to the ulnar nerve and artery. The ulnar nerve branches, giving off a deep motor branch, which courses along the ulnar side of the hamate hook, and one to two predominantly sensory branches that lie superficial to the hamate hook [9]. The flexor carpi ulnaris is seen proximal to the pisiform bone.

Short and long axis images should be obtained from the volar wrist crease to the thenar muscles. Adjustments in transducer position are needed to compensate for the normal contour of the wrist in this area.

Dorsal wrist and hand — Structures on the dorsal aspect of the wrist and hand are superficial and a high frequency transducer is recommended for performing an US examination. The sonographer should use a short axis on the dorsal aspect of the wrist to allow proper identification of the extensor tendons. Once a tendon is identified, it is followed in short axis plane to its distal insertion. Evaluation in long axis is generally less useful but can be used to confirm findings.

●First dorsal wrist compartment (image 8) – The first dorsal compartment of the wrist includes the abductor pollicis longus (ventral) and extensor pollicis brevis (dorsal). These are examined with the patient's wrist halfway between pronation and supination, with the probe over the lateral aspect of the radial styloid. The abductor pollicis longus is followed distally over the scaphoid to assess possible accessory tendons. The radial artery can be seen deep, and the sensory branch of the radial nerve superficial, to the first compartment. Scanning from proximal to distal, the radial nerve and its branches can be seen crossing from ventral to dorsal over these tendons.

●Second dorsal wrist compartment (image 9) – The second dorsal compartment includes the extensor carpi radialis longus and extensor carpi radialis brevis tendons, which can be seen when moving the probe ulnarly from the first compartment to the second compartment, with the probe in short axis and the patient's palm facing the examination table. After the second compartment tendons are identified at the wrist, the probe can be moved along the second compartment proximally. The abductor pollicis longus and extensor pollicis brevis muscles can be seen crossing superficial to the tendons at the distal third of the forearm.

●Third dorsal wrist compartment and scapholunate ligament (picture 1 and picture 2) – The best way to distinguish the second from the third compartment is to find Lister's tubercle over the dorsal radius and use it as a landmark. The extensor pollicis longus (EPL) tendon is found at the medial side of the tubercle and can be followed distally in short axis to its insertion. The EPL tendon crosses over the second compartment distally. The scapholunate ligament can be found by scanning distally from Lister's tubercle in short axis. A slight ulnar deviation of the wrist may be helpful to identify this ligament.

●Fourth and fifth dorsal wrist compartments (image 11 and image 12) – The transducer can be placed in the short axis over the mid dorsal wrist to examine the fourth compartment, which includes the extensor digitorum and extensor indicis tendons. These tendons are found over the distal radius just ulnar to the third compartment. Dynamic evaluation performed while the patient flexes and extends specific fingers can help the clinician to differentiate among the individual tendons of the fourth compartment. To examine the fifth compartment, the probe is kept in short axis. The extensor digiti minimi is found over the distal radial ulnar joint just ulnar to the fourth compartment. Dynamic scanning performed by having the patient flex and extend their small finger is helpful for identifying the extensor digiti minimi.

●Sixth dorsal wrist compartment (image 13) – The extensor carpi ulnaris (ECU) is best examined with the wrist in slight radial deviation. For this compartment, the long axis and short axis views are equally important (image 20). The ECU tendon should be viewed in supination and pronation to assess for subluxation. At the gap between the styloid and the radius lies the triangular fibrocartilage complex. This should be examined in both long and short axis (image 5).

SONOGRAPHIC PITFALLS AND APPEARANCE OF WRIST AND HAND PATHOLOGY

Tendinopathies — Normal tendon appears hyperechoic with a fibrillar echotexture and uniform thickness [10]. Tendon pathology, including tenosynovitis, tendinosis, and tendon tear, has a different appearance on ultrasound (US). Tenosynovitis is characterized by distention of the tendon sheath with anechoic or hypoechoic fluid (image 6), synovial hypertrophy, or thickening of the tendon sheath itself with possible hyperemia [11]. Tendinosis is characterized by hypoechoic tendon enlargement with variable hyperemia on color or power Doppler imaging. A partial-thickness tendon tear will appear as an anechoic defect, whereas a full thickness tendon tear manifests as an echoic defect with retraction of the torn tendon ends. Dynamic evaluation is a useful technique to assess tendon subluxation, dislocation, or tear [11].

US can be a useful to evaluate inflammatory arthritis because it can help diagnose joint inflammation before initiation of arthritis treatment, assess response to treatment, and guide percutaneous aspiration or injection [12].

Synovial hypertrophy and cortical irregularities — Synovial hypertrophy is a common US finding associated with inflammatory arthritis. Such hypertrophy appears hypoechoic, or less commonly isoechoic or hyperechoic, compared with subdermal fat [13]. Synovial hypertrophy can involve any synovial space, such as a joint recess or tendon sheath, and may demonstrate hyperemia when examined with color or power Doppler imaging. Power Doppler imaging is more sensitive for detecting synovial hypertrophy compared with conventional color Doppler imaging [14].

Bone erosions are another sign of inflammatory arthritis. They appear as a focal discontinuity or irregularity of the bone surface seen in two perpendicular planes [13]. If a sonographer identifies synovial hypertrophy, a thorough scan of joint surfaces should be performed looking for erosions. Bone irregularities may be seen in psoriatic arthritis, osteoarthritis, gout, and after trauma.

Carpal tunnel syndrome — US is a useful diagnostic test for carpal tunnel syndrome (CTS). The characteristic US finding of any peripheral nerve entrapment is a hypoechoic and enlarged nerve at and just proximal to the entrapment site, with a transition to normal size distal to the site [15]. The median nerve is best seen in the short axis where the hypoechoic nerve fascicles and surrounding hyperechoic connective tissue create a characteristic honeycomb appearance (image 15 and image 16 and image 17 and image 18) [16]. CTS is discussed in detail separately. (See "Carpal tunnel syndrome: Clinical manifestations and diagnosis".)

Of note, the flexor carpi radialis and palmaris longus tendons can be mistaken for the median nerve, but attention to the differences in US appearance can help clinicians avoid this error. A normal tendon demonstrates anisotropy and appears hypoechoic when the transducer is toggled, whereas only some of fascicles of a peripheral nerve will demonstrate anisotropy.

Ulnar collateral ligament of the thumb — US can be used to assess ulnar collateral ligament (UCL) injuries of the thumb (commonly known as "gamekeeper's thumb" or "skier's thumb"). The use of US for this purpose is reviewed separately. (See "Ulnar collateral ligament injury (gamekeeper's or skier's thumb)", section on 'Diagnostic imaging'.)

ADDITIONAL ULTRASOUND RESOURCES — Instructional videos demonstrating proper performance of the ultrasound examination of the wrist and related pathology can be found at the website of the American Medical Society for Sports Medicine: volar wrist US exam, dorsal wrist US exam, ulnar wrist US exam, sports US wrist-hand pathology, US guided interventional procedures of the wrist and hand. Registration must be completed to access these videos but no fee is required.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Musculoskeletal ultrasound".)

SUMMARY AND RECOMMENDATIONS

●Use of ultrasound wrist examination – The wrist is susceptible to a variety of injuries and conditions. Due to the relatively superficial location of a majority of the wrist structures, many of these pathologic conditions can be assessed using ultrasound (US). For evaluation of the wrist and proximal hand in particular, US offers the ability to visualize small joints and articulations, and adjacent structures, both statically and dynamically, with high resolution. Imaging of structures such as the flexor and extensor tendons and the median nerve can be performed from different perspectives. (See 'Uses, advantages, and limitations of wrist and hand ultrasound' above.)

●Anatomy – An understanding of wrist anatomy is essential for interpreting US images. A focused discussion of wrist anatomy as it pertains to the US examination is provided above, while a more detailed discussion of general wrist anatomy is provided separately. (See 'Ultrasound examination of the wrist and hand' above and "Anatomy and basic biomechanics of the wrist".)

●Examination performance – US of the wrist is relatively straightforward due to the superficial location of most of the structures of interest. A systematic approach to the US examination of the wrist is best. The standard approach divides the joint and adjacent portions of the hand into four regions: volar wrist and hand midline; volar wrist and radial hand; volar wrist and ulnar hand; and, dorsal wrist and hand. Performance of the US examination for each region is described in the text. (See 'Ultrasound examination of the wrist and hand' above.)