The carpal bones are arranged into proximal and distal rows. The proximal row contains three bones: the scaphoid, the lunate, and the triquetrum. These are joined by the scapholunate and lunotriquetral ligaments. The distal row contains the trapezium, trapezoid, capitate, and hamate. There is also a sesamoid bone located in the flexor carpi ulnaris (FCU) tendon called the pisiform. The two rows must move in synchrony during flexion, extension, and ulnar/radial deviation to allow smooth movement of the wrist. Disruption of the normal biomechanics of the carpus can result in significant functional problems.1–4
2. Idler RS. Anatomy and biomechanics of the digital flexor tendons. Hand Clin 1985;1(1): 3–11
3. Lewis OJ, Hamshere RJ, Bucknill TM. The anatomy of the wrist joint. J Anat 1970;106(Pt 3):539–552
4. Macconaill MA. The mechanical anatomy of the carpus and its bearings on some surgical problems. J Anat 1941; 75(Pt 2):166–175 2. When considering wrist anatomy, which one of the following is true? The carpal bones are unusual in that they have no muscle or tendon attachments. Instead they are joined by a complex set of ligamentous structures. The ligaments of the carpus may be subdivided as intrinsic and extrinsic. The intrinsic ones link the carpal bones to one another, whereas the extrinsic ones link the carpal bones to the radius and ulna. There are two, not three, functional columns of the carpus. Although there are 8 carpal bones, there are 14 bones involved in the articulations of the carpus. The proximal row of the carpus articulates with the distal radius and ulna and the distal row articulates with the five metacarpals. The pisiform is a sesamoid bone forming a lever arm for the flexor carpi ulnaris (FCU) (not FCR) tendon and is not a true carpal bone.1–4
The proximal row of the carpus is formed by the scaphoid, lunate, and triquetrum. It is a highly mobile unit, which is held by balanced competing forces between the distal radius and triangular fibrocartilaginous complex (TFCC), and the distal carpal row. These forces tend to push the scaphoid into flexion, and the triquetrum into extension. The lunate is held suspended between these two competing forces of rotation by tough scapholunate and lunotriquetral ligaments. These ligaments normally allow the proximal row to function as one gently twisting unit as the wrist moves. In the normal wrist, as the scaphoid flexes in radial deviation, the lunate and triquetrum follow to a degree due to the ligamentous attachments. When there is ligamentous damage, there is dissociation between the three bones and they no longer move smoothly in relation to one another. c c L L Volar inclination lunate with volar subluxation of capitate Dorsal inclination lunate with dorsal subluxation of capitate Fig. 74.1 Carpal instability dissociative (CID). (Adapted from Wolfe SW, Garcia-Elias M, Kitay A. Carpal instability nondissociative. J Am Acad Orthop Surg 20:575–585, 2012.) Distal carpal row Proximal carpal row Fig. 74.2 Carpal instability nondissociative (CIND) represents radiocarpal and/or midcarpal joint instability with no break between bones within either the proximal carpal or distal carpal row. (Adapted from Wolfe SW, Garcia-Elias M, Kitay A. Carpal instability nondissociative. J Am Acad Orthop Surg 20:575–585, 2012.) If the proximal row is the intercalated segment of the wrist, one can consider the lunate to be the intercalated segment of this row. When the scapholunate ligament is disrupted, the scaphoid tends to slump into flexion and the unrestrained lunate tilts dorsally in extension, pulled in part by its attachment to the triquetrum. Therefore, as the lunate rotates into dorsal tilt, there is a dorsal intercalated segment instability (DISI) deformity. Where the lunotriquetral ligament is disrupted, the lunate can then flex with the scaphoid and tilt volarly, hence VISI deformity. So, in a lateral radiograph, the direction of tilt of the lunate is the key factor that defines a DISI versus a VISI and the cause is primarily a ligamentous injury in the proximal row, or a scaphoid fracture, as part of the progressive range of perilunate injuries, mild to severe. A DISI deformity is characterized by extension of the lunate in the lateral view with flexion of the scaphoid, giving a scapholunate angle greater than 60 degrees (Fig. 74.3). A VISI deformity is characterized by a reduced scapholunate angle less than 30 degrees.1,2
There are two key radiographic features of scapholunate ligament disruption. They are the Terry Thomas and cortical ring signs. The Terry Thomas sign reflects an increased gap between the scaphoid and the lunate. It refers to a famous English comedian with a large gap between his central upper incisors. The cortical ring sign (also called the “signet ring sign”) represents a hyperflexed scaphoid wherein the distal pole is seen on end and appears as a cortical ring within 7 mm of the proximal pole. The scapholunate ligament is a b-shaped structure that connects the dorsal, proximal, and volar surfaces of the scaphoid and lunate. When this ligament is injured, it usually pulls away from the scaphoid and remains attached to the lunate. This allows unwanted movement between the scaphoid and lunate leading to chronic wrist problems. A VISI deformity (or VISI sign) refers to volar angulation of the lunate in the lateral view. This occurs with disruption of the lunotriquetral ligament rather than the scapholunate ligament (which would result in dorsal angulation of the lunate, or DISI). The spilled teapot sign indicates volar displacement of the lunate on a lateral radiograph in association with a more severe perilunate injury (stage IV). The cortical ring or signet ring sign is a term also used to describe radiographic signs seen in bronchiectasis when the dilated bronchus and accompanying artery branch are seen in cross-section. Normally the two should be the same diameter, but in this condition the dilated airway appears larger. The Tram track sign also refers to bronchiectasis where the dilated airways are shown in horizontal rather than cross-sectional orientation. There is no wedding band sign described in radiology.1–4
A positive Watson test corresponds to a “clunk” felt during dynamic wrist loading. The Watson (scaphoid shift) test assesses scaphoid instability (Fig. 74.4). DISI VISI R R L L C C Fig. 74.3 In dorsal intercalated segment instability (DISI), the lunate tilts dorsally. In volar intercalated segment instability (VISI), the lunate tilts volarly. (C, capitate; L, lunate; R, radius.) It particularly stresses the scapholunate ligament but may be positive in other problems affecting carpal stability. The test is performed as follows: The examiner holds the scaphoid in full extension by placing pressure over the tubercle on the volar side, while the wrist is in full extension and ulnar deviation. The examiner’s thumb prevents normal flexion of the scaphoid as the wrist is moved from ulnar to radial deviation and pressure is maintained over the tubercle on the volar aspect. The movement is then reversed. As the rest of the carpus moves, the restrained scaphoid has to “catch up” with the lunate and other bones. This occurs gradually if ligament integrity is normal. If the scapholunate ligament is damaged, or another disruption to carpal integration is present, the scaphoid can be restrained in the abnormal position for a prolonged period and palpated as a bulge on the dorsum of the wrist. As the other carpal bones move, the scaphoid has to jump back into position in the scaphoid fossa of the radius. This usually reproduces pain or a “clunk.” However, a slight clunk or discomfort can occur even in individuals with normal ligament integrity.1–2
Mayfield et al1 described four stages of progressive perilunate injury: Stage I: Scapholunate diastasis Stage II: Dorsal dislocation of capitate Stage III: Lunotriquetral dissociation Stage IV: Dislocation of the lunate volarly Any of the features described in options A through E may be seen in a stage III injury with the exception of dislocation of the lunate into the carpal tunnel, which would render this a stage IV injury. Median nerve paresthesias are common following perilunate injury and extended carpal tunnel decompression is frequently required as a result. Purely ligamentous injuries occur along the lesser arc, while fracture dislocations such as with a styloid or scaphoid fracture occur along the greater arc. As such, a radial styloid fracture or lunotriquetral ligament rupture could be seen in a stage III injury. The space of Poirier represents a weak zone in the volar wrist capsule and is usually torn in perilunate injuries.1
Unless there is a transscaphoid fracture dislocation, there is always some scapholunate ligament damage in perilunate injuries. A dorsal ligament-sparing capsular flap has been described by Berger1 which comprises a chevron with the apex ulnarward over the triquetrum to preserve integrity of the dorsal radiocarpal and dorsal intercarpal ligament fibers (Fig. 74.5). While this approach is popular with many surgeons, there is insufficient outcome data to prove superiority over a simple dorsal capsular incision and some would argue that the wrist will be immobilized anyway for a sufficient period to avoid subsequent instability due to dorsal ligament insufficiency. The lunate is found only in the carpal tunnel in stage IV injuries. A volar incision is often employed to decompress the median nerve, to repair the volar capsule, and to aid in relocation of a completely dislocated lunate.1,2 Fig. 74.4 Watson (scaphoid shift) test.
Brunelli and Brunelli1 described using a distally based strip of half of the FCR tendon passed volar to dorsal through the scaphoid and anchored onto the distal radius. This has since been modified by several authors. Six months after the injury is too late to undertake successful K-wire stabilization or direct ligament repair with a bone anchor. A ligament reconstruction with FCR or extensor carpi radialis longus (ECRL) should be considered only if the joint surfaces are healthy. If degenerative changes are seen, denervation of the wrist or various methods of intercarpal fusion may be considered instead. A radiolunate fusion is employed to reduce pain from the radiolunate articulation. A radioscapholunate fusion addresses pain from the radioscaphoid articulation. Both procedures are used in the setting of degenerative arthritis rather than an acute ligament injury.
The Geissler grading system is based on the appearance of the scapholunate ligament, the alignment of the carpus, and the ability to pass a probe between the scaphoid and lunate: Grade 1: There is attenuation or hemorrhage of the scapholunate interosseous ligament (SLIL) and there is no midcarpal malalignment. Grade II: Attenuation/hemorrhage of the SLIL and step-off/incongruency of carpal alignment. A slight gap between carpals (less than width of probe) DIC H C Td Tm S Tr L DST DRL Dorsal Fig. 74.5 Dorsal ligaments of the wrist. (C, capitate; DIC, dorsal intercarpal ligament; DRL, dorsal radiocarpal ligament; DST, dorsal scaphotriquetral ligament; H, hamate; L, lunate; S, scaphoid; Td, trapezoid; Tm, trapezium; Tr, triquetrum.) (Adapted from Butterfield WL, Joshi A, Lichtman D. Lunotriquetral injuries. J Am Soc Surg Hand 2:195–203, 2002.) Grade III: Step-off/incongruency of carpal alignment (and scapholunate gap large enough to pass probe between carpals Grade IV: Step-off/incongruency of carpal alignment, gross instability and 2.7-mm arthroscope can pass through the gap between the scaphoid and lunate. The usual equipment for a wrist arthroscopy is a 2.7-mm, 30-degree viewing scope with traction apparatus and a wet technique to aid inspection of the tightly packed carpus. The numbered portals are described according to the extensor compartments. Therefore, the 3–4 portal lies between the third and fourth compartments. The 3–4 portal is the most common first portal, and this is where the extensor pollicis longus (EPL) tendon is at most risk. It is also the most common viewing portal.1
A flexed scaphoid gives a cortical ring appearance in the anteroposterior (AP) view (Fig. 74.6). The proximal carpal row includes the scaphoid, lunate, and triquetrum. The lunate is referred to as the intercalated segment, because its movements are heavily influenced by the ligamentous complexes between these three bones. When the lunotriquetral ligament complex is disrupted, the lunate becomes volarly angulated giving a scapholunate angle of less than 30 degrees. When the scapholunate ligament complex is disrupted, the lunate becomes more dorsally angulated under the influence of the lunotriquetral ligament complex. This increases the scapholunate angle to more than 60 degrees in the lateral view. Progressive perilunate injuries may be purely ligamentous, passing along the lesser arc, or when fractures of the radial styloid, scaphoid, capitate, or triquetrum occur, this is considered a greater arc injury. A proximal pole capitate fracture is usually part of a greater arc injury and therefore not an isolated injury. The Terry Thomas sign is a radiographic finding where there is an increase scapholunate gap secondary to scapholunate ligament disruption. The cortical ring sign represents hyperflexion of the scaphoid.1