Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

extensor tendon originating from the lateral epicondyle, and the medial images show the components of the common flexor tendon originating from the medial epicondyle. In the sagittal plane, the ulnar nerve is often well visualized running posterior to the medial epicondyle. The common flexor tendon lies in close association with the ulnar nerve, and both structures can often be visualized on the same sagittal image.

■ Wrist/Hand

Axial Images

The best use of axial images is for evaluating the median and ulnar nerves (Fig. 2.18) and the contents of the carpal tunnel and Guyon canal. Additionally, the flexor and extensor tendons crossing the wrist joint are best visualized in this plane (Fig. 2.19). Many of the muscles in the forearm exert

force not only on the elbow but also on the wrist and hand. Muscles in the distal forearm can be classified by location (superficial or deep).

There are five superficial muscles in the dorsal aspect of the distal forearm:

•Extensor carpi radialis brevis

•Extensor carpi radialis longus

•Extensor digitorum

•Extensor digiti minimi

•ECU

Four superficial muscles are found in the distal forearm:

•Flexor carpi radialis

•Flexor carpi ulnaris

•Flexor digitorum superficialis

•Palmaris longus (not always present)

There are four deep muscles in the dorsal aspect of the distal forearm:

•Abductor pollicis longus

•Extensor pollicis brevis

Superficial palmar arch

Palmar aponeurosis cut

Hook of hamate

Volar carpal lig.

(roof of Guyon’s tunnel)

Pisiform bone

Flexor carpi ulnaris tendon

Ulnar a.

Ulnar n.

Palmaris longus tendon (cut)

Flexor pollicis brevis m.

Abductor pollicis m.

Superficial radial a.

Common digital branches of median n.

Transverse carpal lig.

Superficial radial a.

Median n.

Antebrachial fascia

Radial a.

Flexor carpi radialis tendon

Insertion of extensor tendon at base of distal phalanx

C

Fig. 2.22 A sagittal T1-weighted image of the wrist showing the normal appearance of the flexor digitorum profundus and flexor digitorum superficialis tendons, as well as the triangular fibrocartilage.

phalanx of the thumb. Unlike the other muscles described in this section, the abductor pollicis brevis has no function at the wrist joint, and thus is considered a hand muscle.

In the axial plane, the distal radioulnar joint is examined at the sigmoid notch of the radius. Particular osseous structures, such as the hook of the hamate, and the articulations between carpal bones can be assessed on axial images. The extrinsic carpal ligaments (Fig. 2.24), seen as uniformly low intensity structures in close relationship with the wrist capsule, may be accentuated with intraarticular contrast. Axial images of the digits provide cross-sectional visualization of small anatomic structures such as the flexor tendons, extensor mechanism, volar plates, and neurovascular bundles (Figs. 2.21 and 2.25).

Coronal Images

Coronal plane images provide useful anatomic information about the wrist and hand, and show well the osseous structures and their respective relationships (Fig. 2.26). Small

specialized planes. The abductor pollicis longus and extensor pollicis brevis tendons are seen within the medial/volar aspect of the wrist at the level of the volar aspect of the scaphoid and lunate. Also within the volar aspect of the wrist are the radioscaphocapitate ligament and the radiolunotriquetral ligament, which extend in the ulnar direction from the radial styloid. Located slightly ulnar to these ligaments is the radioscapholunate ligament (Fig. 2.24). These three carpal ligaments are low in signal intensity and are often seen on the same image in the coronal plane.

Despite the advantages of coronal images for evaluation of the TFCC and intercarpal ligaments, the variable courses of the tendons and neurovascular structures crossing the wrist and hand joints make evaluation of these structures di cult in the coronal plane, and therefore these structures are primarily assessed on axial images. On the dorsal coronal images, the extensor digiti minimi tendon is seen as it courses obliquely along the ulnar side of the triquetrum. The extensor pollicis longus and the extensor carpi radialis brevis are separated by Lister’s tubercle, which shows fatty marrow signal intensity. On the volar coronal images, the flexor tendons are seen coursing deep to the flexor retinaculum, which appears as a dark, transverse band. The flexor tendons appear as hypointense bands and can be followed as they pass through the carpal tunnel between the trapezium and the hook of the hamate. The median nerve is intermediate in signal, slightly brighter than that of the adjacent tendons.

Superficial palmar arch

Fig. 2.25 A 3D illustration of the volar (red) and dorsal (pink) vasculature in the left wrist and hand.

The radial and ulnar styloid may be evaluated for fractures on coronal images. The joints, including the distal radioulnar, radiocarpal, intercarpal, and carpometacarpal joints, can also be evaluated for degenerative or traumatic changes. The articular surfaces of the carpal bones show intermediate signal intensity.

Sagittal Images

The sagittal plane is useful for depicting the longitudinal course of structures and providing an orthogonal section for bones in the wrist and hand. Information from sagittal images can be used to evaluate the TFCC (Fig. 2.22) and overall carpal alignment, especially with regard to the scapholunate and capitolunate articulations (Figs. 2.27 and 2.28). Deformity of the scaphoid and abnormalities of the pisotriquetral joint are also examined in this plane. Fractures of the other carpal bones, including the hook of the hamate and the lu-

nate, are also well visualized. The course of the flexor and extensor tendons is well shown on sagittal images of the digits, as is the course of the median nerve in the wrist.

■ Hip

Axial Images

The hip (femoroacetabulum), a diarthrodial joint, is an articulation between the acetabulum and the head of the femur (Fig. 2.29). The acetabulum is formed by the union of the ilium, ischium, and pubis; is normally oriented approximately 45 degrees caudally; and has between 14 and 26.5 degrees of anteversion (averages: men, 18.5 ± 4.5 degrees; women, 21.5 ± 5.0 degrees).8 The normal femoral neck–shaft angle ranges between 125 and 140 degrees.8,9 Given the complex 3D geometry of the hip joint, MRI of the hip should use all

three standard planes of imaging and a specialized plane along (parallel to) the femoral neck. The muscles of the hip can be grouped according to function or anatomic location (medial, anterior, lateral, and posterior). There is no single accepted grouping technique, but some form of a systematic review should be performed. Functional muscle grouping is a logical technique:

•Abductors: gluteus medius, gluteus minimus, and tensor fascia lata

•Adductors: pectineus, gracilis, adductor longus, adductor brevis, and adductor magnus

•Flexors: iliopsoas, rectus femoris, sartorius

•Extensors: gluteus maximus, hamstrings

•External rotators: piriformis, obturator externus, obturature internus, superior gemelli, inferior gemelli, and quadratus femoris

Although most of the musculature in the region of the hip is best evaluated on axial images (Figs. 2.30 and 2.31), the

hamstrings and gluteus medius and minimus are more easily evaluated in the coronal plane (Fig. 2.32).

Generally, in addition to the conventional axial images, oblique axial images oriented along the axis of the femoral neck are also obtained. These oblique images allow visualization of the head–neck junction and can aid in evaluating anatomy associated with femoroacetabular impingement. Axial images allow for good visualization of the anterior and posterior portions of the labrum (Fig. 2.31), which are seen as low signal intensity structures. Axial images are also useful for identifying the regional neurovascular bundles, specifically the sciatic nerve, obturator, and femoral neurovascular bundles; in these bundles, the nerves are seen in cross-section as intermediate signal structures, and often discrete fascicles can be discerned.

The gluteus maximus, gluteus medius, and gluteus minimus can be identified and di erentiated by fascial divisions. The tensor fascia latae is located anterior to the gluteus medius (Fig. 2.31). At the level of the inferior pubic ramus, the

Fig. 2.28 A sagittal T1-weighted image (A) and artist’s sketch (B) of the wrist at the radiolunate articulation showing the normal relationship of the radius, lunate, hamate, and fourth (ring finger)

metacarpal. Long segments of the flexor digitorum superficialis and profundus tendons are seen as they pass through the carpal tunnel.