of Traumatic Carpal Instability

Fig. 1

PA view in neutral position. (a) Without marking, (b) with marking. Harmonious three Gilula arches, ulnar styloid in the extension of the medial ulnar cortex (arrow head), extensor carpi ulnaris groove in relation to fossa (white arrow) suppress 2 and 3

A continuity between the medial cortex of the ulna and the ulnar styloid

ECU gutter in the middle of the fossa [19]

For the lateral view, the criteria are (Fig. 2):

Fig. 2

Lateral view in neutral position. (a) Without marking, (b) with marking: Superposition of the radius and ulna. Pisiform between scaphoid tubercle and anterior facet of capitate (arrow). Lunate axis (line 1) perpendicular to the line connecting the anterior and posterior horns (dotted line). Scaphoid axis (line 2). Capitate axis (line 3). Scapholunate angle alpha. Capitolunate angle beta

Superposition of the radius and ulna

Pisiform projects between the anterior cortex of the capitate posteriorly and the distal pole of the scaphoid anteriorly [20]

On these views, we can note:

Carpal arches described by Gilula to assess the alignment of the two carpal rows. The first arch is formed by the superior convex border of the scaphoid, lunate and triquetrum and the second by their concave borders. The third arch is formed by the proximal borders of the capitate and hamate [21]. These arches delineate harmonious curves in neutral position. In radial or ulnar deviation, we can observe physiological abutment [22].
The regularity of these lines (on PA).
All lines do not normally exceed 3 mm thickness. The opposing articular surfaces are parallel, and in the absence of flexion, any overriding indicates the presence of a fracture or subluxation. The scapholunate space must be carefully scrutinized. In fact, in the axial plane, this interval is parallel in only 80 % and divergent with respect to the anterior and posterior horns of the lunate in 15 % of cases [23]. Thus, the measure of this space must be taken at the middle. Scapholunate diastasis is considered if the interval exceeds 3 mm. This may be physiologic in lunotriquetral synostosis or inherent laxity (bilateral comparative x-rays are recommended), or pathologic in association to ligament rupture (Fig. 3) [24, 25].

Fig. 3

Scapholunate diastasis. Scapholunate interval is not widened in neutral position (a). SL diastasis on AP view with 20° pronation (b)
Carpal angles (lateral view).

The lunate axis is defined by the line perpendicular to the tangent connecting the two horns of the lunate. The scaphoid axis passes through the centre of the tubercle, waist and base of the scaphoid. The axes of the radius and the capitate are calculated by dropping a perpendicular to the line connecting the two equidistant points on the anterior and posterior borders of these two bones. The normal scapholunate angle is between 30° and 70° with a mean value of 55°. It increases in extension instability (DISI) and decreases in flexion instability (VISI). The radiolunate and capitolunate angles range between −15° and +15°. They increase in DISI or VISI (Fig. 4). The theoretical collinearity of the axes of the radius, lunate, capitate and third metacarpal is actually rarely seen (only 11 % normal subjects).

Fig. 4

Carpal instability. DISI dorsal tilt of the lunate and increased scapholunate angle, VISI ventral tilt of the lunate

The study of carpal dynamics is usually done to confirm clinical or radiographic suspicion of carpal instability. Gilula proposes PA views in neutral position, ulnar and radial deviation, a clenched fist PA view, lateral views in neutral position, flexion and extension. The clenched fist position increases intra-articular pressure and unmasks scapholunate diastasis [26]. Lawand proposes this test on both sides whilst clenching a pencil [27]. The interpretation of these views requires knowledge of the combined carpal movements in the sagittal and coronal planes (Fig. 5). In radial deviation, the first carpal row flexes. The scaphoid is shortened and shows the ring sign at its distal portion representing the tubercle seen escaping. The lunate follows the movement and appears triangular due to the displacement of its pointed posterior horn. In ulnar inclination, the first carpal row extends. The scaphoid elongates, exposing its waist. The lunate becomes quadrangular due to displacement of its rounded anterior horn which becomes more visible [28].

Fig. 5

Carpal dynamics in radial and ulnar inclination. (a) Radial inclination: The first carpal row is in flexion. The scaphoid is short and shows the ring sign. Triangular shape of the lunate is due to the pointed shape of its posterior horn. Physiological rupture of Gilula arch 1 regarding the lunotriquetral interval. (b) Ulnar inclination: The carpal bones are in extension. The scaphoid is elongated. Quadrangular shape of the lunate due to the large and rounded shape of its anterior horn

Radiography remains an investigation of low sensitivity. As repeatedly shown by experimental studies [29], the presence of radiographic signs of instability denotes extensive ligament lesions generally associated with complete or partial intrinsic and extrinsic ligaments, thus the need for complementary investigations [30].

To summarize:

Radiographic signs for DISI on PA view in neutral are scapholunate diastasis, superposition of the scaphoid and capitate, ring sign of the scaphoid, quadrangular shape of the lunate. On lateral view, they are the increase of scapholunate, capitolunate and radiolunate angles (Fig. 6).

Fig. 6

Dorsal instability (DISI) at 1 month post traumatic. (a, b) Radiographs at day 0 showing no abnormality. (c, d) Control at 1 month shows a DISI. Pa shows shortened scaphoid with a ring sign, superposition of the scaphoid and capitate denoting rotational displacement, quadrangular lunate. Lateral view confirms the dorsal tilt of the lunate with a widening of the scapholunate angle

Radiographic signs for VISI are decrease of scapholunate angle and increase of capitolunate and radiolunate angles.

5 Ultrasound

The use of ultrasound for diagnosis of lesions of wrist ligaments is very recent [31–33]. It is an investigation of low sensitivity but high specificity which can be a useful cheap complement to the clinical examination. It requires, however, high-quality equipment with high-frequency ultrasound. The dorsal portion of the scapholunate ligament may be seen in most cases, the TFCC in one out of two cases and rarely, the dorsal portion of the lunotriquetral ligament. The interosseous ligaments are examined in transverse cuts from the dorsal side, whilst varying the degree of wrist flexion. The diagnosis of rupture depends on the appearance of the normal fibrous structure which is replaced by a zone of hypoechogenicity (Fig. 7) [34].

Fig. 7

Ultrasound of the scapholunate ligament. Comparative study of the dorsal portion; SC scaphoid, L lunate. (a) Normal SL (arrow), (b) Hypoechoic zone denoting rupture (arrow)

6 CT Scan

Simple CT scan without injection is not indicated in studying wrist ligaments. However, it shows associated osseous lesions perfectly.

7 MRI

Most studies use the 1.5 T system. A cadaveric study using a low-field machine showed limited results [35]. Several more recent studies compared the same sequences at 1.5 and 3.0 T [36–38]. The subjective quality and signal–noise relation was significantly higher at 3.0 T. The technical considerations of positioning are such that the wrist is seldom in a neutral position and thus the anatomical relations are modified. The most recent 3 T MRI study gives 100 % specificity and 89 and 82 % sensitivity for full-thickness scapholunate and lunotriquetral lesions, respectively [39].

8 Arthrography, Arthro-CT and Arthro-MRI

Opaque arthrography, notably triple arthrography with successive punctures of the midcarpal, radiocarpal and distal radioulnar joints, is but the precursor of CT or MR arthrography. The opacification of these compartments by contrast material – iodides for CT and gadolinium salts for the MRI – allows an exhaustive analysis of the different articular portions of the scapholunate and lunotriquetral ligaments.

The scapholunate ligament closes the proximal part of the interval. It is horseshoe-shaped and is formed of three anatomically and functionally distinct portions [40, 41]. The dorsal portion is short, transverse and trapezoidal. Composed of thick and tight collagen bands, it is the strongest part of the ligament. It forms the axis of rotation between the scaphoid and the lunate. The proximal or intermediate portion resembles a meniscus with its triangular shape and fibrocartilaginous structure. It is proximally attached to the radioscapholunate facet and is the weakest part of the ligament. The palmar portion is long and slopes obliquely below and inwards. It is formed of finer and more loosely arranged collagen bands, allowing an anterior displacement of both bones in flexion. The scaphoid has a greater arc in flexion than the lunate due to a smaller curvature of its proximal pole.

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