6 The Wrist and Hand: Diagnostic Imaging

10.1055/b-0038-161011

6 The Wrist and Hand: Diagnostic Imaging

Abstract

An ultrasound examination of the wrist and hand is one of the most common ultrasound examinations conducted in patients with rheumatological disease and is able to detect early signs of pathology. Such signs will depend on the advancement of the disease. In osteoarthritis, ultrasound has been shown to be more sensitive than clinical examination in detection of joint inflammation in patients with erosive OA. In patients with rheumatoid arthritis, ultrasound is able to detect significant synovitis not determined by clinical examination—‘subclinical’ synovitis. An ultrasound examination of the wrist and hand should be conducted using a linear transducer of a high frequency (12-18 MHz). While a larger footprint probe allows better overall anatomical resolution, a smaller ‘hockey stick’ probe should be utilized for smaller structures.

6.1 Diagnostic Imaging of the Wrist and Hand: Introduction

Examination of the wrist and hand will be dependent on the specific structure and pathology suspected from a thorough clinical examination. Based on this examination it would be normal to scan one or two specific structures. In addition to static scanning dynamic imaging should be included particularly when imaging tendons and ligaments to fully assess the patency of these structures.

Imaging includes the following:

Wrist joint—volar
- Flexor retinaculum.
- Median nerve.
- Flexor pollicis longus tendon.
- Flexor digitorum profundus and superficialis tendons.
- Flexor carpi radialis longus tendon and radial artery.
- Guyon’s canal and the ulnar nerve and artery.
- Flexor carpi ulnaris tendon.
Wrist joint—dorsal
- The six dorsal compartments and extensor retinaculum.
- Proximal radiocarpal and midcarpal joints.
- Scapholunate joint and ligament.
Fingers and thumb
- Metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints.
- Pulley system (A1–A5).
- First carpometacarpal joint of the thumb.
- Ulnar collateral ligament of the thumb.

6.1.1 Wrist Joint—Volar

Carpal Tunnel: Transverse Scan

The patient is seated facing the clinician with the forearm supinated and hand facing upward resting on a table. The probe is placed so that it rests transversely at the level of the distal palmer crease in the axial plane over the flexor tendons and wrist joint (Fig. 6‑1 , Fig. 6‑2 , Fig. 6‑3 , Fig. 6‑4 ).

Fig. 6.1 Transverse scan of the volar aspect of the wrist and carpal tunnel. The probe is placed at the level of the distal palmer crease. The radial aspect of the probe should be placed so that it overlays the scaphoid tubercle and the ulnar aspect of the probe should overlay the pisiform.

Fig. 6.2 Transverse image of the carpal tunnel and its contents. From the radial aspect can be seen the scaphoid tubercle (ST) with the overlying tendon of flexor carpi radialis (FCR). Immediately medial to this can be seen the tendon of flexor pollicis longus (FPL). Next to this the median nerve (*white arrowhead*) can be seen immediately deep to the flexor retinaculum (*yellow arrows*). To the ulnar side the pisiform (PI) can be seen with Guyon’ canal (*yellow ellipse*). The tendons of flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) can be seen deep below the median nerve and Guyon’s canal.

Fig. 6.3 Coronal view of the carpal tunnel and hand demonstrating the carpal and digital tendon sheaths on the palmar surface of the right hand. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Fig. 6.4 Cross-section of the right wrist at the level of the carpal tunnel. The carpus, the bony elements of the wrist, forms an arch which is convex on the dorsal side of the hand and concave on the palmar side. The groove on the palmar side, the sulcus carpi, is covered by the flexor retinaculum, a sheath of tough connective tissue forming the carpal tunnel. The flexor retinaculum is attached radially to the scaphoid tubercle and the ridge of trapezium, and on the ulnar side to the pisiform and hook of hamate. The tendons of the flexor digitorum superficialis and profundus pass through a common ulnar sheath, while the tendon of the flexor pollicis longus passes through a separate radial sheath. Superficial to the carpal tunnel and the flexor retinaculum, the ulnar artery and ulnar nerve pass through Guyon’s canal. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Guyon’s Canal: Transverse Scan

The patient is seated facing the clinician with the forearm supinated and hand facing upward resting on a table. The probe is placed so that it rests transversely at the level of the distal palmer crease in the axial plane over the flexor tendons and wrist joint. The probe may be aligned more medially to ensure suitable visualization of Guyon’s canal at the ulnar aspect of the carpal tunnel (Fig. 6‑5 , Fig. 6‑6 , Fig. 6‑7 ).

Fig. 6.5 Transverse scan of the volar aspect of the wrist and carpal tunnel. The probe is placed at the level of the distal palmer crease. The ulnar aspect of the probe should be placed so that it overlays the pisiform. Guyon’s canal is situated immediately lateral to the pisiform.

Fig. 6.6 Transverse image of the medial side of the carpal tunnel and Guyon’s canal. The pisiform (PI) should be used as a landmark with Guyon’s canal immediately lateral to this. At this level the ulnar nerve (*white arrowhead*) appears as an oval structure transversely. Immediately lateral to this the ulnar artery may be seen (*white star*). If the probe is moved distally toward the hook of hamate, the ulnar nerve may be seen to split into a superficial sensory and deeper motor branch. The insertion of the tendon of flexor carpi ulnaris can be seen superficial to the pisiform onto which it joins (*curved arrow*). Yellow arrows, flexor retinaculum.

Fig. 6.7 Cross-section of the right wrist at the level of the carpal tunnel. In this enlarged view the relationship and relative positions of the flexor tendons and neurovascular structures may be seen. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Wrist—Pathology: Carpal Tunnel Syndrome

The median nerve should be assessed at the level of the carpal tunnel at the distal wrist crease, again immediately proximal to the carpal tunnel at the level of the pronator quadratus muscle and again at the level of the midforearm. In the normal patient, the cross-sectional area of the nerve should be approximately 9 mm² throughout its entire length. In patients with carpal tunnel syndrome this cross-sectional area can significantly increase at the level of the carpal tunnel with an associated flattening of the nerve (Fig. 6‑8 a–c).

Fig. 6.8 (a) Transverse image of the median nerve at the carpal tunnel (*yellow arrow*). The nerve appears enlarged and flattened. The cross-sectional area measures 25 mm2. (b) Transverse image of the median nerve (*yellow arrow*) at the level of the pronator quadratus muscle (*white arrowheads*). The nerve appears rounded rather than flattened. The cross-sectional area is reduced to 10 mm². (c) Transverse image of the median nerve at the level of the midforearm (*yellow arrow*). The nerve appears rounded rather than flattened. The cross-sectional area is reduced to 7 mm².

Wrist—Pathology: Carpal Tunnel Syndrome

See Fig. 6‑9 , Fig. 6‑10 , and Fig. 6‑11.

Fig. 6.9 Transverse image of the median nerve at the wrist (*yellow arrow*) demonstrating marked thickening of the nerve and associated flattening.

Fig. 6.10 Longitudinal image of the median nerve (*yellow arrows*) at the level of the carpal tunnel. There appears to be a mild swelling of the nerve as it enters the tunnel (*white arrowhead*). Doppler imaging demonstrates a mild intraneural vascularity suggestive of carpal tunnel syndrome.

Fig. 6.11 Transverse image of the median nerve at the level of the carpal tunnel (*yellow arrow*). The nerve appears both thickened and flattened. In this image a needle (*curved arrow*) may be seen entering the carpal tunnel from the right side of the screen to be placed immediately deep to the nerve.

6.1.2 Wrist Joint—Dorsal

Dorsal Wrist—Overview of the Six Dorsal Compartments

The patient is seated facing the clinician with the forearm resting on a table. The probe is placed so that it rests transversely over the dorsal compartment to be assessed. The clinician should identify each tendon within its specific compartment from dorsal compartment one through six transversely and then longitudinally. The patient should be asked to actively move the wrist and fingers appropriate to each compartment to allow the clinician to further dynamically assess the tendons (Fig. 6‑12 , Fig. 6‑13 , Fig. 6‑14 ).

Fig. 6.12 Schematic representation of the dorsal compartments of the wrist. There are six separate compartments formed by the extensor retinaculum. Assessment of all six compartments would be unlikely with the clinician being directed by a thorough clinical examination of the patient. I, extensor pollicis brevis (EPB) and abductor pollicis longus (APL); II, extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL); III, extensor pollicis longus (EPL); IV, extensor digitorum longus (EDL) and extensor indicis (EI); V, extensor digiti minimi (EDM); VI, extensor carpi ulnaris (ECU); white star, Lister’s tubercle.

Fig. 6.13 Transverse image of the dorsal wrist compartments. From left to right: Compartment I extensor pollicis brevis and abductor pollicis longus; compartment II extensor carpi radialis brevis and extensor carpi radialis longus; compartment III extensor pollicis longus; compartment IV extensor digitorum longus and extensor indicis; compartment V extensor digiti minimi; compartment VI extensor carpi ulnaris. Note: compartment I and VI cannot be clearly seen in this image as they are positioned around the radial and ulnar aspect of the wrist, respectively, and need to be imaged separately. White star, Lister’s tubercle.

Fig. 6.14 Transverse section of the distal radius and ulna demonstrating the dorsal compartment and their respective tendons. Compartment I, extensor pollicis brevis and abductor pollicis longus; compartment II, extensor carpi radialis brevis and extensor carpi radialis longus; compartment III, extensor pollicis longus; compartment IV, extensor digitorum longus and extensor indicis; compartment V, extensor digiti minimi; compartment VI, extensor carpi ulnaris. (Reproduced from Schuenke, Schulte, and Schumacher, Atlas of Anatomy, 2nd edition, ©2014, Thieme Publishers, New York. Illustration by Karl Wesker/Markus Voll.)

Dorsal Compartment I—Abductor Pollicis Longus and Extensor Pollicis Brevis

The patient’s forearm is positioned so that it is halfway between supination and pronation with the thumb facing upward. The probe is placed transversely over the first dorsal compartment at the level of the radial styloid. A smaller hockey stick probe may be useful when examining the individual dorsal compartments. As for all the dorsal compartments the tendons should first be identified and examined using a transverse view and then further evaluated in longitudinal view (Fig. 6‑15 , Fig. 6‑16 , Fig. 6‑17 , Fig. 6‑18 , Fig. 6‑19 ).