Carpal Tunnel and Median nerve

4.1 Palmar Side

4.1.1 Carpal Tunnel and Median nerve

Wrist evaluation can be started either on the palmar or the dorsal side. The patient must be sitting in front of the examiner, with the upper limb lying on the table.

Fig. 4.1aScheme of the proximal carpal tunnel. FCR, flexor carpi radialis tendon; FCU, flexor carpi ulnaris tendon;

m, median nerve; a, ulnar artery; u, ulnar nerve; FPL, flexor pollicis longus tendon; circles, flexor digitorum superficialis tendons ; *, flexor digitorum profundus tendons; arrowheads, retinaculum; ST, scaphoid tubercle; Pi, pisiform;

L,lunate; T, triquetral bone

Fig. 4.1bScheme of the distal carpal tunnel. FCR, flexor carpi radialis tendon; m, median nerve; a, ulnar artery; s, superficial sensitive branch of the ulnar nerve; d,deep motor branch of the ulnar nerve; FPL, flexor pollicis longus tendon; circles, flexor digitorum superficialis tendons; *, flexor digitorum profundus tendons; arrowheads, retinaculum; T, tubercle of trapezium; t, trapezoid; C, capitate; H, hook of the hamate

Fig. 4.2Position of the wrist to evaluate the ventral compartment

Fig. 4.3b Axial scan of the proximal section of carpal tunnel. Sc, scaphoid; Pi, pisiform; L, lunate. The arrowshows the median nerve between flexor retinaculum (arrowheads) and flexor digitorum superficialis (circles) and profundus (*) tendons. Note the “arched” appearance of the retinaculum and at the oval shape of the median nerve. FCR, flexor carpi radialis tendon; ua, ulnar artery; UN, ulnar nerve; FPL, flexor pollicis longus tendon; FCU, flexor carpi ulnaris tendon

Fig. 4.3aProbe position to evaluate the proximal section of the carpal tunnel

Fig. 4.5aProbe position to evaluate the distal part of the carpal tunnel

Fig. 4.5bAxial scan of the distal carpal tunnel.

Arrow, median nerve;

H,hamate; T, trapezium.

The distal part of the tunnel is smaller than the proximal part, the flexor retinaculum (arrowheads) is more flat and the median nerve has a smaller antero-posterior di- ameter. a, ulnar artery;

FPL, flexor pollicis longus tendon; circles, flexor digitorum superficialis tendons;

*, flexor digitorum profundus tendons

Fig. 4.6Longitudinal scan of the carpal tunnel shows the median nerve (*) over the flexor tendons (tt). Ca, capitate;

L,lunate

Fig. 4.7bAxial scan of ulnar nerve (arrowheads) between ulnar artery (Doppler signal in red) and pisiform (Pi)

4.2 Dorsal Side

4.2.1 Extensor Tendon Compartments

To maintain an anatomical order, the dorsal extensor compartments are described below from the radial to ulnar side, from the first to sixth compartment (Fig. 4.8). However, note that inexperienced operators should begin the US evaluation of the dorsal aspect of the wrist from a small bony landmark of the distal radius (the Lister’s tubercle) that separates the second and the third compartment. This is par- ticularly true when common anatomical vari- ants that change the number of tendons contained in each compartment are encountered (see below).

Palm must be placed on the table, in a neu- tral position (Fig. 4.9), except for the evaluation of the I and the VI compartments (see below). A small pillow can be placed under the wrist to improve the visibility of extensor tendons (Fig. 4.10).

The probe must be placed on a transverse plane on the dorsal side of wrist to detect the six extensor tendon compartments on the short axis. Compartments are numbered from I to VI beginning from the radial side.

Each tendon must be scanned on the short axis, followed up to its distal insertion and also scanned during dynamic maneuvers (finger flexion and extension).

4.2.1.1 First Compartment

The first compartment contains the abductor pollicis longus (radial) and extensor pollicis brevis (ulnar) tendons (Fig. 4.11).

The position of tendons contained in the first compartment can be easily detected by

visual inspection, as they form the radial edge of the anatomical snuff box (Fig. 4.12a). The wrist must be kept in an intermediate position between pronation and supination and the probe must be placed on the lateral side of radial styloid (Fig. 4.12b). The retinaculum contains the two tendons (Fig. 4.12c). Follow the abductor pollicis longus up to its insertion onto the scaphoid and check if there is an accessory tendon.

Sometimes the tendon sheath is split into two parts by a fibrous hyperechoic septum that separates the two tendons. This septum can be seen when evaluating the compartment on the short axis.

The detection of accessory tendons and of the fibrous septum is important as they can favor the occurrence of tenosynovitis.

Theabductor pollicis longusis the most lateral of the deep muscles in the posterior compartment of the forearm. It arises from the dorsal side of ulna, distally to the supinator crest, from the interosseous membrane and from the dorsal side of the radius. Its distal tendon crosses the second extensor tendon compartment and takes insertion on the first metacarpal bone. Some fibers also insert onto the trapezium and others join the extensor pollicis brevis tendon.

Theextensor pollicis brevisis a deep muscle of the posterior compartment of the forearm. At this level, it is medial to the abductor pollicis longus muscle. It arises from the ulna, the interosseous membrane, and the dorsal side of the radius. Its distal tendon crosses the second extensor tendon compartment and inserts on the proximal phalanx of the thumb.

Fig. 4.9Wrist position to evaluate the dorsal side

Fig. 4.10Position of the wrist on a small pillow to improve the visibility of the extensor tendons

Fig. 4.8Panoramic anatomical scheme of the extensor tendon compartments. APL, abductor pollics longus tendon;

EPB, extensor pollicis brevis tendon; ECRL, extensor carpi radialis longus tendon; ECRB, extensor carpi radialis brevis tendon; EPL, extensor pollicis longus tendon; EIP, extensor indicis proprius tendon; EDC, extensor digitorum communis tendon; EDQ, extensor digiti quinti tendon; ECU, extensor carpi ulnaris tendon; R, radis; U, ulna

Fig. 4.12aAnatomical snuff box (*). Radial side:

abductor pollicis longus and extensor pollicis brevis (arrowheads); ulnar side: extensor pollicis longus (arrows)

Fig. 4.12bProbe position to evaluate the first extensor compartment

Fig. 4.12cAxial scan of the first compartment:

APL, abductor pollicis longus tendon; EPB, extensor pollicis brevis tendon; V, cephalic vein;

R,radius. Note that the location of the cephalic vein can be extremely variable

Fig. 4.11Anatomical scheme of the first extensor compartment; APL, abductor pollicis longus tendon;

EPB, extensor pollicis brevis tendon; R,radius

the second compartment (Fig. 4.15). This intersection is critical, especially in subjects that perform repetitive movements of the hand (e.g., oarsmen), who develop the so-called

“intersection syndrome”. The presence of a small bursa can also be detected. This patho- logic condition can be confused with the more common De Quervain tenosynovitis that typi- cally affects the first compartment.

Theextensor carpi radialis brevismuscle arises from the anterior aspect of the lateral epicondyle, the antebrachial fascia, the radial collateral ligament, and the intermus- cular septum. The muscle is very small and immediately becomes a tendon that runs on the lateral aspect of the radius along with the extensor carpi radialis longus tendon.

Distally, it inserts on the dorsal aspect of the third metacarpal bone.

Fig. 4.13Anatomical scheme of the second extensor compartment: ECRL, extensor carpi radialis longus tendon; ECRB, extensor carpi radialis brevis tendon

Fig. 4.14aProbe position to evaluate the second extensor compartment

Fig. 4.14bAxial scan of the second compartment. ECRB, extensor carpi radialis brevis tendon; ECRL, extensor carpi radialis longus tendon; EPL, extensor pollicis longus tendon; L, Lister’s tubercle

Fig. 4.15Axial scans at the distal third of the forearm show the intersection between the first (I) and second (II) extensor tendon compartment

Fig. 4.16Anatomical scheme of the third extensor tendon compartment; EPL, extensor pollicis longus tendon; R, radius

Fig. 4.17bAxial scan of the third compartment. EPL, extensor pollicis longus tendon; ECRB, extensor carpi radialis brevis tendon; ECRL, extensor carpi radialis longus tendon; L, Lister’s tubercle

Fig. 4.18Axial scans at the distal third of the forearm show intersection between the third (arrowheads) and second (II) extensor tendon compartment; LT, Lister’s tubercle

Fig. 4.17aProbe position to evaluate the third extensor compartment

posterior aspect of the ulna and interosseous membrane. Its distal tendon enters the fourth extensor compartment, then joins the extensor digitorum tendon of the second ray over the corresponding metacarpophalangeal joint.

The extensor digiti minimiis a superficial muscle lying in the posterior compartment of the forearm, medial to the extensor digitorum muscle. It arises together with the extensor digitorum from the posterior aspect of the lateral epicondyle and the antebrachial fascia. It enters the fifth extensor compartment, then joins the extensor digitorum tendon of the fifth ray over the corresponding metacarpophalangeal joint. Note that the floor of the fifth compartment is made by a fibrous band and the tendon does not lie on the bone, like the other five compartments.

Fig. 4.19Anatomical scheme of the fourth and fifth extensor compartments. EIP, extensor indici proprius tendon; EDC, extensor digitorum communis tendon; R, radius;

U, ulna useful to differentiate it from the extensor dig-

itorum tendons.

In order to differentiate the two tendons of the fourth compartment (Fig. 4.20b) and the extensor of the little finger tendon (Fig. 4.20c), make dynamic scans while patient flexes and extends fingers.

The extensor of the little finger tendon runs in a space between the radium and ulna and does not have a bony plane below it.

Theextensor digitorumis a superficial muscle lying in the posterior-lateral compartment of the forearm. It arises from the posterior side of the lateral epicondyle, the radial collateral ligament, the annular ligament and the antebrachial fascia. At the middle third of the forearm, it splits into three bundles: the lateral separates into two tendons, while the others

Fig. 4.20aProbe position to evaluate the fourth and fifth compartments

Fig. 4.20bAxial scan on the dorsal wrist. Arrowheads, extensor digitorum tendons; *, extensor indici proprius tendon; R, radius; EPL, extensor pollicis longus (third compartment); LT, Lister’s tubercle; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus

Fig. 4.20cAxial scan of the fifth compartment. U, ulna; void arrowhead, extensor of the little finger tendon; R, radium; IV, tendons of fourth compartment

4.2.2 Distal Radio-Ulnar Joint

The probe must be moved proximally over the distal aspect of the radius and ulna (Figs. 4.24, 4.25a, b).

Fig. 4.21Anatomical scheme of the sixth extensor tendon compartment. ECU, extensor carpi ulnaris tendon; U, ulna The extensor carpi ulnaris is a superficial

muscle lying in the posterior compartment of the forearm, arising medially to the extensor digiti minimi muscle, with branches also inserting on the posterior aspect of the ulna.

Its bundles are directed medially and its distal tendon enters the sixth compartment, then inserts on the fifth metacarpal bone.

Fig. 4.22aProbe position to evaluate the sixth extensor compartment

Fig. 4.22bAxial scan of the sixth compartment. Arrowheadsindicate the extensor carpi ulnaris tendon on the short axis; U, ulna

Fig. 4.23 TFC, triangular fibrocartilage; ECU, extensor carpi ulnaris (long axis);

U,ulnar styloid process; P, pyramidal

Fig. 4.25aProbe position to evaluate the distal radio- ulnar joint

Fig. 4.25bAxial scan of the distal radio-ulnar joint.

R, radius; U, ulna; *, joint space

The exam can be commenced either from the dorsal or the palmar side of the hand.

Dalam dokumen Normal Ultrasound Anatomy of the Musculoskeletal System (Halaman 50-68)