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MUSCULOSKELETAL AND VASCULAR EMERGENCIES IN THE EXTREMITIES

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Multidetector CT of Carpal Injuries: Anatomy, Fractures, and Fracture-Dislocations1 CME FEATURE See accompanying test at http:// www.rsna.org /education /rg_cme.html

LEARNING OBJECTIVES FOR TEST 6 After reading this article and taking the test, the reader will be able to: ■■Discuss

the significance of carpal injuries and the role of imaging in diagnosis of carpal fractures and dislocations.

■■Describe

the risk for development of avascular necrosis in different carpal bone fractures.

■■List

the features of carpal fractures and perilunate injuries.

Rathachai Kaewlai, MD • Laura L. Avery, MD • Ashwin V. Asrani, MD Hani H. Abujudeh, MD • Richard Sacknoff, MD • Robert A. Novelline, MD Fractures and dislocations of the carpal bones are more common in young active patients. These injuries can lead to pain, dysfunction, and loss of productivity. Conventional radiography remains the primary imaging modality for evaluation of suspected carpal fractures and dislocations. However, multidetector computed tomography (CT) is playing an increasingly important role, especially in the following situations: (a) when results from initial radiographs are negative in patients with suspected carpal fractures, (b) when initial radiographic findings are indeterminate, and (c) when knowledge of the extent of carpal fractures or dislocations is required before surgical treatment. The advantages of multidetector CT include quick and accurate diagnosis with availability in most emergency centers. Multidetector CT can easily display the extent of carpal fractures and dislocations, often depicting fractures that are occult at radiography. In addition, with multiplanar (two-dimensional) and volumetric (three-dimensional) reformation, pathologic conditions and anatomic relationships are better perceived. This information can be easily conveyed to orthopedic and trauma surgeons and can be crucial for surgical treatment and planning. ©

RSNA, 2008 • radiographics.rsnajnls.org

TEACHING POINTS See last page

Abbreviation:  3D = three-dimensional RadioGraphics 2008; 28:1771–1784 • Published online 10.1148/rg.286085511 • Content Codes: 1 From the Division of Emergency Radiology, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, 55 Fruit St, FND-210, Boston, MA 02114. Recipient of a Cum Laude award for an education exhibit at the 2007 RSNA Annual Meeting. Received February 8, 2008; revision requested March 12 and received April 1; accepted April 7. H.H.A. receives research support from the Bracco Group; all other authors have no financial relationships to disclose. Address correspondence to R.K. (e-mail: [email protected]).

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Introduction Fractures of the carpal bones are common, with an annual incidence of 159 per 100,000 in the United States. Scaphoid fractures represent 50%–80% of all carpal fractures and are more common in young men. The remaining carpal fractures are also more common in young men and are frequently seen in older women (1). The diagnosis of carpal fractures and dislocations traditionally relies on conventional radiography. However, owing to the complexities of carpal anatomy and the limitations of conventional radiography, many carpal fractures may be overlooked. This may lead to delayed treatment and subsequent wrist dysfunction (2). Computed tomography (CT) can depict radiographically occult carpal fractures (3–6) and is frequently used for the diagnosis of complex carpal fracture. CT can assist surgical planning by providing detailed depiction of the position and alignment of fracture lines and fracture fragments. In this article, we discuss the normal anatomy of the carpus, illustrate carpal fractures and dislocations on multiplanar and volumetric reformatted CT images, and correlate CT findings with those from conventional radiography.

Normal Anatomy of the Wrist A complex unit of eight carpal bones intricately articulates to form the carpus (Figs 1–3). The position of the carpus is influenced proximally by the shape of the radius, ulna, and triangular fibrocartilage and distally by the metacarpals. Interactions between the eight carpal bones produce motion of the carpus with flexion-extension and radioulnar deviation as major wrist movements. Interaction with the distal radioulnar joint allows the carpus to rotate along the longitudinal axis of the forearm. The eight carpal bones and their corresponding ligaments can be divided into two horizontal rows. The proximal carpal row consists of the scaphoid, lunate, and triquetrum. The pisiform does not belong to the proximal row but may act indirectly on the triquetrum (7,8). The proximal carpal row is regarded as an intercalated segment between the radius and the distal carpal row. It is important in maintaining stability of the wrist by coordinating the movement and controlling forces transmitted from the hand to the forearm and vice versa. The distal carpal row consists of the trapezium, trapezoid, capitate, and hamate. These bones form a rigid transverse arch that is more stable than the proximal row, supporting five metacarpals. Ligamentous support of the wrist is complex. The ligaments are categorized as either extrinsic or intrinsic. The extrinsic ligaments connect the radius or ulna and the carpus, whereas intrinsic ligaments link adjacent carpal bones (8,9).

Figure 1.  Normal anatomy of the carpal bones. Diagram of the wrist (frontal view) shows the eight carpal bones and the three carpal arcs (Gilula arcs), which are shown as pink (arc I), blue (arc II), and red (arc III) lines. C = capitate, H = hamate, L = lunate, P = pisiform, S = scaphoid, Tm = trapezium, Td = trapezoid, Tr = triquetrum.

Carpal bone blood supply is unusual because it frequently enters the distal half of the bones. Hence, the proximal portion of the bone is at risk for avascular necrosis if the bone suffers a fracture with disruption of blood flow. There are three patterns of intraosseous vascularization of the carpus, which determine the risk of developing avascular necrosis or nonunion after a fracture (8,10). First, a single-vessel supply is seen in the scaphoid, capitate, and approximately 20% of all lunates. These carpal bones are most vulnerable to avascular necrosis. The second pattern is seen in the trapezoid and hamate, which have two nonarticular nutrient arteries but lack a consistent intraosseous anastomosis. Therefore, the fracture fragments may be at risk for avascular necrosis. The third pattern is seen in the trapezium, triquetrum, pisiform, and approximately 80% of all lunates. In this pattern, two nonarticular nutrient arteries with consistent intraosseous anastomosis provide redundant blood supply. Hence, avascular necrosis rarely occurs in this pattern of vascularization. Carpal arcs (Gilula arcs or lines) (11) (Fig 1) are three smooth arcs examined on frontal radiographs obtained with the wrist in a neutral position. Posteroanterior or anteroposterior wrist

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Kaewlai et al  1773 Figures 2, 3.  (2) Frontal (a, b) and lateral (c, d) radiographs (a, c) and three-dimensional (3D) CT images (b, d) show the normal wrist. C = capitate, H = hamate, L = lunate, P = pisiform, S = scaphoid, Td = trapezoid, Tm = trapezium, Tr = triquetrum. (3) CT appearance of the normal wrist. (a) Coronal reformatted CT image obtained in the midcoronal plane shows the capitate (C), hamate (H), lunate (L), scaphoid (S), trapezium (Tm), trapezoid (Td), and triquetrum (Tr). (b) Sagittal reformatted CT image obtained at the midcarpal level shows the capitate (C) and lunate (L). (c) Axial CT image obtained at the level of the hamate hook shows the capitate (C), hamate (H), trapezium (Tm), and trapezoid (Td).

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radiographs are correctly obtained in the neutral position if the long axis of the third metacarpal is coaxial with that of the distal radius. Arc I outlines the proximal surface of the scaphoid, lunate, and triquetrum. Arc II represents the smooth arc that defines the distal surface of these same three carpal bones. Arc III outlines the proximal surface of the capitate and hamate. An evaluation may be compromised by radial or ulnar deviation (12). When drawing these lines, use only the major curvatures of the bones. The continuity of the carpal arcs should be assessed on all frontal wrist radiographs. Disruption of one of these arcs suggests an abnormality at that site. In the evaluation of the neutral lateral radiograph, a normal coaxial alignment of the radius, lunate, and capitate should be expected.

Fractures of the Proximal Carpal Row Scaphoid Fractures Scaphoid fracture is the most common carpal fracture, occurring predominantly in active men with a peak prevalence in the 2nd to 3rd decades (8). Typically, the injury is due to hyperextension. A common clinical problem encountered with scaphoid fractures is delayed diagnosis. Nondisplaced fractures may be initially overlooked on conventional radiographs, hence an injury may be dismissed as a sprain. An inappropriately treated or untreated fracture may result in complications including progressive fragment displacement, avascular necrosis, malunion, delayed union, and nonunion. The end result may be pain, dysfunction, and early degenerative change. Given the young patient population, this can be of great clinical significance with considerable functional disability, resulting in time off from work, loss of income, and interference with recreational activities. The scaphoid is the largest bone of the proximal carpal row with a configuration of a boat (scaphion in Greek means boat). It is the important link between the proximal and distal carpal rows and acts as an intercalated segment between

Figure 4.  Anatomic (Mayo Clinic) classification of scaphoid fractures. 1 = distal articular surface, 2 = tuberosity, 3 = distal third, 4 = waist or middle third, 5 = proximal pole.

the lunate proximally and the trapezium and trapezoid distally. The scaphoid can be arbitrarily divided into three parts: proximal third, middle third, and distal third. The waist of the scaphoid refers to the middle third of the bone. On the distal third of the scaphoid, a scaphoid tuberosity is a rounded bony prominence on the palmar surface, and a distal articular surface describes the area where the scaphoid articulates with the trapezium and trapezoid. Approximately 80% of scaphoid surfaces are articular facets covered in articular cartilage. This results in reduced capacity for periosteal healing and increased risk of delayed union and nonunion if fractured (8,13,14). The scaphoid receives blood supply from branches of the radial artery; 80% of its blood supply enters the scaphoid waist dorsally and supplies the proximal portion in a retrograde fashion. Only a single intraosseous vessel provides blood supply, thus further increasing the risk of avascular necrosis if fracture results in vascular injury (15). Avascular necrosis occurs in 13%–50% of scaphoid fractures, with a higher prevalence if the fracture is located at the proximal pole and with increasing amount of displacement (16,17). Fractures of the scaphoid occur most frequently from a fall on an outstretched hand with forced dorsiflexion of the wrist. Other possible mechanisms include compression or avulsion of the tuberosity and avulsion of the proximal pole by a scapholunate ligament. Scaphoid fractures can be classified by anatomic location into proxi-

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Figure 5.  Scaphoid waist fracture. (a, b) Coronal reformatted (a) and 3D (b) CT images show a displaced transverse fracture of the scaphoid waist (arrow). (c) Sagittal reformatted image shows apical-dorsal angulation of the fracture (dashed line).

Figure 6.  Proximal pole scaphoid fracture. Frontal radiograph (a), coronal reformatted CT image (b), and 3D CT image (c) show a transverse fracture of the scaphoid at its proximal pole (arrow).

mal pole, middle third (waist), distal third, distal articular surface, and tuberosity according to the Mayo Clinic classification (Fig 4) (18). Waist

fractures (Fig 5) are the most common type of scaphoid fractures, accounting for 80% of cases, followed by proximal pole fractures (Fig 6). Acute fractures are described by their obliquity to the longitudinal axis of the scaphoid (horizontal oblique, vertical oblique, or transverse), comminution, and displacement. There is increasing mechanical instability in fractures with increasing degrees of obliquity, comminution, and displacement (18). Definitive diagnosis of acute scaphoid fracture is made with radiographic confirmation. A routine

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wrist radiography protocol may include posteroanterior, lateral, and radial and ulnar oblique projections. In some institutions, a posteroanterior view with the wrist in ulnar deviation (scaphoid view) may be obtained in addition to the routine views. Despite multiple radiographic projections, up to 30% of scaphoid fractures cannot be visualized at initial radiographic examinations (8,16). Therefore, in the past, patients with clinical findings of scaphoid fracture but negative initial radiographs underwent long thumb-spica cast immobilization, followed by repeat examinations and radiography after 10–14 days to confirm the diagnosis. Although this approach remains an accepted method at some centers, most patients in this group do not actually have scaphoid fractures and are needlessly subjected to thumb immobilization (16,19). There are two options to reduce unnecessary cast immobilization: wrist CT or magnetic resonance (MR) imaging. MR imaging can display carpal fractures well (16,20–22), but the examination is more difficult to arrange, needs longer examination time (30–40 minutes), and has a high cost. CT is more readily available, faster (6–12 seconds of examination time), and less costly. CT has an increasing role in the evaluation of patients with suspected scaphoid fractures but negative radiographs. The reported sensitivities and specificities of CT are 89%–97% and 85%– 100%, respectively. The high negative predictive value of CT (96.8%–99%) makes it very useful for ruling out a fracture (3,5,6).

Lunate Fractures Lunate fractures have a prevalence of 3.9% of all carpal fractures (8). The lunate, as its name suggests, has a moon-shaped configuration when viewed on lateral radiographs. It consists of a body, a volar pole, and a dorsal pole. The lunate acts as the keystone of the proximal carpal row, sitting in the central position of the carpus. Lunate fractures may result in carpal instability, nonunion, and avascular necrosis if left unrecognized. Two patterns of vascular supply to the lunate have been described. A single-vessel supply is seen in 20% of all lunates; the remaining 80% receive two nonarticular nutrient arteries with consistent intraosseous anastomosis (8). The former pattern poses an increased risk of avascular necrosis. Lunate fractures usually occur from direct axial compression from the head of the capitate

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Figure 7.  Lunate fracture. Lateral radiograph (a) and sagittal reformatted CT image (b) show a sclerotic lunate with an acute fracture of the dorsal pole (arrow). This case is an example of Kienböck disease manifesting with an acute lunate fracture.

driven into the lunate. Fractures are classified according to their anatomic location (volar pole, dorsal pole, body) and the orientation of the fracture line (transverse, sagittal) (23). An isolated lunate fracture is often difficult to diagnose radiographically because the lunate overlaps with other carpal bones on lateral radiographs (8,24). CT can show nearly all fractures as well as other associated injuries. There is a possible association of a lunate fracture that fails to unite and the development of Kienböck disease (14). Kienböck disease is an avascular necrosis of the lunate, occurring primarily in young adults. It is a separate entity that mimics a lunate fracture and may be present with superimposed acute fracture (Fig 7). The exact etiology is not known, but it is possibly related to a traumatic event in susceptible individuals with vascular insufficiency.

Triquetral Fractures Triquetral fractures are the second most common carpal fractures with a prevalence of 18.3% (8). The majority of fractures are dorsal ridge fractures, which occur at the dorsal aspect of the triquetrum (Fig 8). They result from impingement of the ulnar styloid process against the dorsal surface of the triquetrum during wrist hyperextension and ulnar deviation. Alternatively, dorsal ridge fractures may occur in acute hyperflexion that results in ligamentous avulsion from the dorsal surface of the triquetrum (14). Dorsal

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Figure 8.  Triquetral fracture. Lateral radiograph (a), sagittal reformatted CT image (b), and 3D CT image (dorsal projection) (c) show an avulsion fracture of the dorsal ridge of the triquetrum (arrow) with overlying soft-tissue edema (* in a and b).

Figure 9.  Pisiform fracture. Frontal radiograph (a), axial CT image (b), and 3D CT image (c) show a transverse fracture of the pisiform (arrow).

ridge fractures are best visualized on lateral radiographs obtained with the wrist in slight pronation. Another less common type of triquetral fracture is a fracture of the triquetral body (2). These commonly occur in conjunction with perilunate dislocations.

Pisiform Fractures Pisiform fractures are uncommon, accounting for 1.3% of all carpal fractures (8). The pisiform is a sesamoid bone enclosed within the flexor carpi ulnaris tendon, articulating with the triquetrum

dorsally. Most pisiform fractures result from a fall on an outstretched hand, causing a direct blow to the pisiform. Pisiform fractures may be linear, comminuted, or chip type with or without associated pisiform dislocation (Fig 9). A less frequent cause of pisiform fracture is an avulsion injury due to a pull of ligaments attached to the pisiform (25). Owing to its close proximity to the ulnar nerve, fractures may cause ulnar nerve injury (2).

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Figure 10.  Trapezium fracture. Frontal radiograph (a) and sagittal reformatted CT image (b) show an avulsion fracture of the trapezial ridge (arrow).

Figure 11.  Trapezoid fracture. Coronal reformatted (a) and 3D (b) CT images show a vertical fracture of the body of the trapezoid (large arrow). There is an associated comminuted fracture of the scaphoid waist (small arrows).

Figure 12.  Capitate fracture. Frontal radiograph (a), 3D CT image (b), and sagittal reformatted CT image (c) show a nondisplaced transverse fracture of the neck of the capitate (large arrow in b and c). The fracture is not visible on the radiograph and only faintly visualized on the 3D image owing to its nondisplacement. Note the associated comminuted fracture of the scaphoid waist (small arrow in a and b).

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the first carpometacarpal joint. The fractures typically involve the first carpometacarpal joint and may be seen with fractures of the base of the first metacarpal or the scaphoid (2).

Trapezoid Fractures Trapezoid fractures account for 0.4% of all carpal fractures (8). The trapezoid is the least commonly fractured carpal bone. When the trapezoid is fractured, the mechanism is usually a high-energy axial blow to the second metacarpal. Trapezoid fractures are commonly associated with other carpal fractures (Fig 11) and may occur with dorsal displacement of the trapezoid (14). Routine wrist radiography may show the fractures; however, CT may provide additional information on the degree of displacement and fractures of adjacent bones.

Capitate Fractures

Figure 13.  Hamate fracture. Axial (a), sagittal reformatted (b), and 3D (c) CT images show a nondisplaced fracture at the base of the hamate hook (arrow).

Pisiform fractures may be overlooked at routine wrist radiography (14,26). Additional imaging such as carpal tunnel radiography or CT may be helpful to detect fractures. On the other hand, the diagnosis may be difficult in patients who have multiple pisiform ossification centers.

Fractures of the Distal Carpal Row Trapezium Fractures Trapezium fractures account for 3%–5% of all carpal fractures (8). The trapezium is the most mobile bone of the distal carpal row (13). Fractures of the trapezium most commonly occur at the trapezial ridge (Fig 10). The trapezial ridge is a vertical prominence on the volar aspect of the trapezium, where ligaments and the flexor retinaculum insert. Trapezial ridge fractures may result from a direct blow to the volar surface of the trapezium or an avulsion injury. They may be overlooked at routine wrist radiography. Carpal tunnel radiography may be helpful to detect this fracture (2,27,28), whereas CT results can be diagnostic. Fractures of the trapezial body are less common than those of the trapezial ridge. They result from an axial loading or shearing force through

Capitate fractures account for 1.9% of all carpal fractures (8). The capitate is the largest of all the carpal bones, supported by strong palmar ligaments. Injuries to this bone are usually due to a high-energy hyperextension force. Fractures are typically transverse in orientation (Fig 12). They may occur in isolation or with other carpal injuries (13,29). The capitate has a rounded head that articulates with the scaphoid and lunate and partially articulates with the hamate. The capitate head is the proximal one-third of the bone. It is covered almost completely with articular cartilage and thus has a limited vascular supply. Therefore, fractures of the capitate head are subject to an increased risk of prolonged healing and avascular necrosis (14).

Hamate Fractures Hamate fractures account for 1.7% of all carpal fractures (8). The hamate hook is the most frequent site of hamate fractures (Fig 13). They are most frequently encountered in athletes participating in racket sports. The fractures typically result from direct compression of the handle of the racket against the protruding hook (2,14). The hook is a prominent rounded projection of the hamate at the palmar nonarticular surface. Its tip is an attachment site for several flexor tendons, muscles, and ligaments (2,8,13,14). Therefore, these soft-tissue attachments may cause displacement of the fractured hook, resulting in delayed healing or nonhealing.

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Figure 14.  Perilunate instability. Perilunate ligaments fail in a sequence from radial to ulnar (I–IV).

Radiographic signs of hamate hook fracture include absence of the hook in an acute displaced fracture or sclerosis in the area of a healing hook fracture. An accessory ossicle (os hamulus proprium) may mimic an old hook fracture (30). Carpal tunnel radiography or CT may be used to diagnose a hook fracture. The hamate may fracture through the body as a result of an axial loading force to a clenched fist (2,14,31). Fractures of the body are commonly associated with dislocations of the fourth and fifth carpometacarpal joints, particularly the coronally oriented fractures (2). Occasionally, hamate body fractures are associated with perilunate dislocations.

Carpal Dislocation

The most common carpal dislocation is perilunate dislocation. These injuries are characterized by severe disruption of the soft tissues and sometimes bones of the wrist with dislocation of the capitate head from the concavity of the distal lunate. They are complex injuries that typically require open reduction and

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Figure 15.  Lesser arc and greater arc injuries. Pure ligamentous injuries occur around the lunate (red line). Perilunate injuries that occur through osseous structures (blue line) are called greater arc injuries.

internal fixation (32). They usually affect young men with an average age of 30 years (8,33–35). Perilunate injuries result from high-energy wrist hyperextension, typically falls from a height, motor vehicle collisions, or sports-related injuries. Perilunate injuries occur in a sequence as the ligaments around the lunate fail in a radial to ulnar direction; this is called progressive perilunate instability. It starts at the scapholunate joint, then proceeds to the lunocapitate and lunotriquetral joints, and finally culminates in complete dislocation of the lunate (Fig 14) (36). Perilunate injuries can occur in two patterns: perilunate dislocation without fracture and perilunate dislocation with associated fracture (Fig 15). Perilunate dislocation (lesser arc injury) is a pure ligamentous disruption around the lunate (Fig 16). Perilunate dislocation with associ- ated fracture of one or more bones around the lunate (scaphoid, trapezium, capitate, hamate, or triquetrum) is called a greater arc injury (Fig 17) (35). Greater arc injuries are twice as frequent as those of the lesser arc (33). For the nomenclature of greater arc injuries, the fracture is mentioned first and is indicated by the prefix

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Figure 16.  Lesser arc perilunate dislocation. (a, b) Frontal radiograph (a) and 3D CT image (b) show a triangular appearance of the lunate (*), disruption of Gilula arcs I and II, and a small avulsion fracture (arrow) in the scapholunocapitate space. (c, d) Lateral radiograph (c) and sagittal reformatted CT image (d) show dorsal dislocation of the rest of the carpal bones along with the hand relative to the lunate (*). Note the associated triquetral fracture (arrow in c).

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Figure 17.  Transscaphoid perilunate dislocation. Frontal (a) and lateral (b) radiographs and 3D CT images (c, d) show disruption of Gilula arcs I and II, a triangular lunate (*), and dorsal dislocation of the rest of the carpal bones along with the hand relative to the lunate, findings consistent with perilunate dislocation. In addition, there is a displaced fracture of the scaphoid waist (large arrow), an avulsion fracture of the lunate (small arrow in a and c), and a fracture of the ulnar styloid process.

“trans-.” The dislocation is mentioned second. For example, a transscaphoid perilunate dislocation is a combination of a scaphoid fracture and a dorsal dislocation of the capitate relative to the lunate. This is the most common type of perilunate injury. Despite severe disruption, up to 25% of perilunate injuries are overlooked at initial examinations (33,35). Radiographic signs include disruption of the carpal (Gilula) arcs, a triangular lunate, and fractures of the carpal bones around the lunate. On the lateral projection, posterior dislocation of the capitate head along with the rest of the hand relative to the lunate is characteristic of perilunate dislocation. The lunate maintains its articulation with the distal radius. A sign of an early stage of perilunate dislocation may be widening of the space between the scaphoid and lunate (Terry-Thomas sign) (37), which suggests scapholunate dissociation (36,38) (Fig 18). Another rare injury that may occur in conjunction with perilunate dislocation is scaphocapitate fracture (32,39), a transverse fracture through the scaphoid waist and capitate. The injury causes

180° rotation of the proximal fragment of the capitate so that the articular surface of the capitate is directed distally. Assessment on lateral radiographs is important for the detection of associated perilunate dislocation. Lunate dislocation is the final stage of perilunate injuries. In this injury, the lunate is dislocated volarly out of the distal radial articulation and the rest of the carpus assumes alignment with the radius. This is called the spilled teacup sign on lateral radiographs (Fig 19). Lunate dislocation is the most severe form of perilunate injuries and is associated with the highest degree of instability (40).

Conclusions

Carpal fractures and dislocations may be overlooked on conventional radiographs. CT with multiplanar and volumetric reformation can be a useful technique to demonstrate occult carpal fractures and to illustrate the complexity and extent of fractures and dislocations. Acknowledgment:  We thank Susanne Loomis, MS, for her wonderful graphics presented in this article.

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Figure 18.  Scapholunate dissociation. Frontal radiograph (a) and corresponding volume-rendered (b) and shaded-surface display (c) CT images show widening of the scapholunate space (*) and a rounded appearance of the scaphoid (S).

Figure 19.  Lunate dislocation. (a–c) Lateral radiograph (a), sagittal reformatted CT image (b), and 3D CT image (c) show the spilled teacup sign, with the lunate (*) dislocating volarly out of the distal radial articulation while the rest of the carpus remains aligned with the radius. (d) Frontal radiograph shows an associated scaphoid fracture (large arrow) and a distal radial fracture (small arrow in c and d). * = lunate.

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References 1. Court-Brown C, Koval KJ. The epidemiology of fractures. In: Bucholz RW, Heckman JD, CourtBrown C, eds. Rockwood and Green’s fractures in adults. 6th ed. Philadelphia, Pa: Lippincott Williams & Wilkins, 2006; 95–143. 2. Papp S. Carpal bone fractures. Orthop Clin North Am 2007;38:251–260. 3. Cruickshank J, Meakin A, Breadmore R, et al. Early computerized tomography accurately determines the presence or absence of scaphoid and other fractures. Emerg Med Australas 2007;19:223–228. 4. You JS, Chung SP, Chung HS, Park IC, Lee HS, Kim SH. The usefulness of CT for patients with carpal bone fractures in the emergency department. Emerg Med J 2007;24:248–250. 5. Adey L, Souer JS, Lozano-Calderon S, Palmer W, Lee SG, Ring D. Computed tomography of suspected scaphoid fractures. J Hand Surg [Am] 2007;32:61–66. 6. Roolker W, Tiel-van Buul MM, Ritt MJ, Verbeeten B Jr, Griffioen FM, Broekhuizen AH. Experimental evaluation of scaphoid X-series, carpal box radiographs, planar tomography, computed tomography, and magnetic resonance imaging in the diagnosis of scaphoid fracture. J Trauma 1997;42:247–253. 7. International Wrist Investigators’ Workshop Terminology Committee. Wrist: terminology and definitions. J Bone Joint Surg Am 2002;84-A(suppl 1):1–73. 8. Gaebler C. Fractures and dislocations of the carpus. In: Bucholz RW, Heckman JD, Court-Brown C, eds. Rockwood and Green’s fractures in adults. 6th ed. Philadelphia, Pa: Lippincott Williams & Wilkins, 2006; 857–908. 9. Cardoso R, Szabo RM. Wrist anatomy and surgical approaches. Orthop Clin North Am 2007;38:127–148. 10. Cooney WP. Vascular and neurologic anatomy of the wrist. In: Cooney WP, Linscheid RL, Dobyn JH, eds. The wrist: diagnosis and operative treatment. St Louis, Mo: Mosby, 1998; 106–123. 11. Gilula LA. Carpal injuries: analytic approach and case exercises. AJR Am J Roentgenol 1979;133: 503–517. 12. Peh WC, Gilula LA. Normal disruption of carpal arcs. J Hand Surg [Am] 1996;21:561–566. 13. Garcia-Elias M, Dobyns JH. Bones and joints. In: Cooney WP, Linscheid RL, Dobyn JH, eds. The wrist: diagnosis and operative treatment. St Louis, Mo: Mosby, 1998; 61–72. 14. Geissler WB. Carpal fractures in athletes. Clin Sports Med 2001;20:167–188. 15. Gelberman RH, Menon J. The vascularity of the scaphoid bone. J Hand Surg [Am] 1980;5:508–513. 16. Adams JE, Steinmann SP. Acute scaphoid fractures. Orthop Clin North Am 2007;38:229–235. 17. Botte MJ, Pacelli LL, Gelberman RH. Vascularity and osteonecrosis of the wrist. Orthop Clin North Am 2004;35:405–421. 18. Linscheid RL, Weber ER. Scaphoid fractures and nonunion. In: Cooney WP, Linscheid RL, Dobyn JH, eds. The wrist: diagnosis and operative treatment. St Louis, Mo: Mosby, 1998; 385–430. 19. Groves AM, Kayani I, Syed R, et al. An international survey of hospital practice in the imaging of acute scaphoid trauma. AJR Am J Roentgenol 2006;187:1453–1456.

RG  ■  Volume 28  •  Number 6 20. Memarsadeghi M, Breitenseher MJ, SchaeferProkop C, et al. Occult scaphoid fractures: comparison of multidetector CT and MR imaging— initial experience. Radiology 2006;240:169–176. 21. Brydie A, Raby N. Early MRI in the management of clinical scaphoid fracture. Br J Radiol 2003;76: 296–300. 22. Gaebler C, Kukla C, Breitenseher M, Trattnig S, Mittlboeck M, Vécsei V. Magnetic resonance imaging of occult scaphoid fractures. J Trauma 1996;41:73–76. 23. Palmer AK, Benoit MY. Lunate fractures: Kienbock’s disease. In: Cooney WP, Linscheid RL, Dobyn JH, eds. The wrist: diagnosis and operative treatment. St Louis, Mo: Mosby, 1998; 431–473. 24. Welling RD, Jacobson JA, Jamadar DA, Chong S, Caoili EM, Jebson PJ. MDCT and radiography of wrist fractures: radiographic sensitivity and fracture patterns. AJR Am J Roentgenol 2008;190:10–16. 25. Cooney WP. Isolated carpal fractures. In: Cooney WP, Linscheid RL, Dobyn JH, eds. The wrist: diagnosis and operative treatment. St Louis, Mo: Mosby, 1998; 474–487. 26. Fleege MA, Jebson PJ, Renfrew DL, Steyers CM Jr, el-Khoury GY. Pisiform fractures. Skeletal Radiol 1991;20:169–172. 27. Palmer AK. Trapezial ridge fractures. J Hand Surg [Am] 1981;6:561–564. 28. Botte MJ, von Schroeder HP, Gellman H, Cohen MS. Fracture of the trapezial ridge. Clin Orthop Relat Res 1992;276:202–205. 29. Adler JB, Shaftan GW. Fractures of the capitate. J Bone Joint Surg Am 1962;44-A:1537–1547. 30. Schmidt H, Freyschmidt L, eds. Arm: carpal bones. In: Borderlands of normal and early pathologic findings in skeletal radiology. New York, NY: Thieme, 1993; 102–105. 31. Hirano K, Inoue G. Classification and treatment of hamate fractures. Hand Surg 2005;10:151–157. 32. Sauder DJ, Athwal GS, Faber KJ, Roth JH. Perilunate injuries. Orthop Clin North Am 2007;38:279–288. 33. Herzberg G, Comtet JJ, Linscheid RL, Amadio PC, Cooney WP, Stalder J. Perilunate dislocations and fracture-dislocations: a multicenter study. J Hand Surg [Am] 1993;18:768–779. 34. Hildebrand KA, Ross DC, Patterson SD, Roth JH, MacDermid JC, King GJ. Dorsal perilunate dislocations and fracture-dislocations: questionnaire, clinical, and radiographic evaluation. J Hand Surg [Am] 2000;25:1069–1079. 35. Kozin SH, Murphy MS, Cooney WP. Perilunate dislocations. In: Cooney WP, Linscheid RL, Dobyn JH, eds. The wrist: diagnosis and operative treatment. St Louis, Mo: Mosby, 1998; 632–650. 36. Mayfield JK. Mechanism of carpal injuries. Clin Orthop Relat Res 1980;149:45–54. 37. Frankel VH. The Terry-Thomas sign. Clin Orthop Relat Res 1978;135:311–312. 38. Manuel J, Moran SL. The diagnosis and treatment of scapholunate instability. Orthop Clin North Am 2007;38:261–277. 39. Vance RM, Gelberman RH, Evans EF. Scaphocapitate fractures: patterns of dislocation, mechanisms of injury and preliminary results of treatment. J Bone Joint Surg Am 1980;62:271–276. 40. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg [Am] 1980;5:226–241.

This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician’s Recognition Award. To obtain credit, see accompanying test at http://www.rsna.org/education/rg_cme.html.

RG

Volume 28 • Volume 6 • October 2008

Kaewlai et al

Multidetector CT of Carpal Injuries: Anatomy, Fractures, and Fracture-Dislocations Rathachai Kaewlai, MD, et al RadioGraphics 2008; 28:1771–1784 • Published online 10.1148/rg.286085511 • Content Codes:

Page 1772 There are three patterns of intraosseous vascularization of the carpus, which determine the risk of developing avascular necrosis or nonunion after a fracture (8,10). First, a single-vessel supply is seen in the scaphoid, capitate, and approximately 20% of all lunates. These carpal bones are most vulnerable to avascular necrosis. The second pattern is seen in the trapezoid and hamate, which have two nonarticular nutrient arteries but lack a consistent intraosseous anastomosis. Therefore, the fracture fragments may be at risk for avascular necrosis. The third pattern is seen in the trapezium, triquetrum, pisiform, and approximately 80% of all lunates. In this pattern, two nonarticular nutrient arteries with consistent intraosseous anastomosis provide redundant blood supply. Hence, avascular necrosis rarely occurs in this pattern of vascularization. Page 1772 Carpal arcs (Gilula arcs or lines) (11) (Fig 1) are three smooth arcs examined on frontal radiographs obtained with the wrist in a neutral position. Page 1776 CT has an increasing role in the evaluation of patients with suspected scaphoid fractures but negative radiographs. The reported sensitivities and specificities of CT are 89%–97% and 85%–100%, respectively. The high negative predictive value of CT (96.8%–99%) makes it very useful for ruling out a fracture (3,5,6). Page 1780 Perilunate injuries occur in a sequence as the ligaments around the lunate fail in a radial to ulnar direction; this is called progressive perilunate instability. It starts at the scapholunate joint, then proceeds to the lunocapitate and lunotriquetral joints, and finally culminates in complete dislocation of the lunate (Fig 14) (36). Page 1780 Perilunate dislocation (lesser arc injury) is a pure ligamentous disruption around the lunate (Fig 16). Perilunate dislocation with associated fracture of one or more bones around the lunate (scaphoid, trapezium, capitate, hamate, or triquetrum) is called a greater arc injury (Fig 17) (35).