Injuries to the Carpal Bones Revisited Derek Lohan, FFR (RCSI),a Carmel Cronin, MRCPI,a Conor Meehan, MRCPI,a Sinead Walsh, FFR (RCSI),a Declan Sheppard, FRCR,b,c and David O’Keeffe, FRCR, FFR (RCSI)a

Falls on the outstretched hand, with resultant pain in the carpal region, account for a significant number of referrals to emergency rooms worldwide. Not only do they represent a significant proportion of the radiological workload arising from emergency rooms, interpretation of the images acquired is often difficult due to the complex anatomy of this region, compounded by an inability to obtain adequate views due to patient discomfort. Often, despite apparently normal radiological examinations, patient discomfort persists, prompting a need for further imaging. It is vital that the radiologist be entirely familiar with the bony and ligamentous anatomy of this body region, as well as possess an understanding of the frequent mechanisms of injury. Using a variety of imaging techniques, we illustrate a spectrum of carpal injuries, common and otherwise, explaining the mechanism and typical appearances of each.

To gain an understanding of the mechanism of carpal injury, a detailed knowledge of the bony and ligamentous anatomy of this complex region is paramount. The eight carpal bones owe their considerable stability and strength to a number of factors, not least the integrity of their multiple ligamentous attachments, working in unison to maintain their articular surfaces in a relatively rigid, yet functional, stance. These ossific structures are arranged in two parallel curved rows, the proximal consisting of scaphoid, lunate, triquetrum, and pisiform, and the distal row including the trapezium, trapezoid, capitate, and From the aDepartment of Radiology, University College Hospital, Galway, Ireland; bDepartment of Radiology, Portiuncula Hospital, Galway, Ireland; and cDepartment of Radiology, Roscommon County Hospital, Co. Roscommon, Ireland. Reprint requests: Derek G. Lohan, FFR (RCSI), David Geffen School of Medicine at UCLA, Peter V. Ueberroth Building, 10945 Le Conte Ave., Suite 3310, Los Angeles, CA 90095-7206. E-mail: dlohan@mednet. ucla.edu. Curr Probl Diagn Radiol 2007;36:164-75. © 2007 Mosby, Inc. All rights reserved. 0363-0188/2007/$32.00 ! 0 doi:10.1067/j.cpradiol.2007.03.002

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hamate. Proximally the carpus articulates with the radius laterally and the triangular fibrocartilage overlying the distal aspect of the ulna medially. The five metacarpal bones articulate with the distal row. The complex arrangement of these bony structures, combined with their apparently haphazard ligamentous support, divides the wrist joint into four separate articulations: the radiocarpal joint, the distal-radioulnar joint, the midcarpal joint, and the carpometacarpal joint, which is further subdivided into small (between the first metacarpal and trapezium) and large components (lying between the carpus and the second, third, fourth, and fifth metacarpals). However, further inspection of the organizational structure of the ligamentous support allows one to appreciate the superbly organized manner in which these ligaments are arranged. An understanding of Taleisnik’s classification of the carpal ligaments into dorsal and palmar extrinsic (those having carpal attachments but extending outside the carpus) and intrinsic (intercarpal, entirely confined within the carpus) aids the reader in understanding the dynamics of this complex anatomical region.1 As the strength of the wrist relies heavily on the integrity of this ligamentous network, complete or partial disruption of any, or a combination of, these ligaments may lead to carpal instability and resultant chronic, often debilitating, wrist pain.2

Carpal Fractures Knowledge of the mechanism of injury often has a high predictive value with regard to the presence or absence of a carpal fracture and, in many cases, is indicative of the type of radiological pathology subsequently seen. Given the anatomical features considered above, one can now readily appreciate how some of the carpal bones are relatively proCurr Probl Diagn Radiol, July/August 2007

FIG 1. (A and B) Conventional frontal radiograph and correlating coronal CT image of a scaphoid waist fracture (arrows) in a 26-year-old male patient sustained during a FOOSH. A Herbert screw was subsequently sited (C).

tected with respect to their neighbors given a traumatic insult. By far the most common mechanism of injury encountered in daily practice is the fall on outstretched hand (FOOSH). Mechanically, impact on a pronated, dorsiflexed wrist joint results in the lunate bone adopting the role of focal-point of articulation of the carpal bones against the radial articular surface. A number of potential outcomes may ensue, ranging from distal radial fractures (be they Greenstick in infants, Salter–Harris-type epiphyseal in older children, or Colles/Smith in adults), avulsion or tearing injuries of the triangular fibrocartilage, distal radioulnar joint disruption, carpal dislocation, carpal fracture, or a combination of more than one of the above.

Scaphoid The scaphoid is the most commonly injured of the carpal bones,3,4 and comment on the integrity of this bone is often the source of much hesitation, with tales of litigation never being far from mind. Radiologists are now well-versed in the recommendation of a repeat radiograph following an interval of several days should pain persist in the region of the anatomical snuff box. The frequency at which a fracture to this bone occurs is testament to its essential role in maintenance of the stability of the carpal structures. Furthermore, knowledge of the unusual blood supply to the proximal pole of this bone has now become part of medical folklore and medical students of all levels are aware of the potential adverse outcomes of interruption to the vascularity and its link to proximal pole avascular necrosis in the setting of a fracture of the scaphoid waist due to impingement of this bone on the styloid process of the radius. Fig 1 illustrates a typical, radiographically appreciable scaphoid fracture. ConCurr Probl Diagn Radiol, July/August 2007

FIG 2. Reconstructed sagittal CT image of an anteroposterior displaced fracture through the body of the lunate bone (arrow).

cern regarding further fragment displacement with subsequent proximal pole avascular necrosis and resultant chronic pain and stiffness was addressed by the placement of a Herbert screw, thus providing internal fixation. Such injury normally occurs on traumatic dorsiflexion and radial deviation of the wrist, in the clinical scenario of FOOSH, with wedging of the scaphoid between the radial articular surface and the remainder of the carpus, particularly the capitate. If clinically suspected, yet radiologically occult, a posteroanterior view with the wrist in ulnar deviation may distract the fragments and make the underlying fracture more apparent.5 165

FIG 3. Conventional radiograph (A), with correlating T2-weighted coronal fat-saturated and T1-weighted coronal MRI images (B and C) of a triquetral fracture (arrows) in a female patient after recent FOOSH and ongoing dorsal wrist pain. Note the considerable associated edema on the MR images.

Furthermore, scaphoid fractures are often associated with other injuries of the wrist, including dislocation of the radiocarpal joint, perilunate dislocation, fracture-dislocation of the distal end of the radius, fracture at the base of the thumb metacarpal, and lunate dislocation.

Lunate More often dislocated than fractured, injury to the lunate bone is not an infrequent occurrence, in the most part occurring secondary to forceful, traumatic dorsiflexion at the wrist joint. On many occasions, patients present with functional wrist deficit rather than pain related to the offending trauma, with dorsal wrist pain and poor wrist strength being the most commonly encountered symptoms. Fig 2 eloquently exemplifies the value of sagittal computed tomography (CT) reconstructions in the assessment of transverse lunate fractures, the fracture margins being clearly depicted without interference from overlying structures. Not infrequently, such patients will be found to have the radiological changes of Kienbock’s disease (lunatomalacia),6 a condition discussed in greater detail below.

Triquetral Failure to adequately examine each of the wrist films obtained may lead to failure to appreciate fracture of the triquetral bone, often visualized on the lateral view only. Characteristically the presence of a fragment of dorsally sited bone, displaced from its donor site on the posterior aspect of the triquetral bone, is seen7 but is commonly unappreciated on conventional radiography (Fig 3). Furthermore, the 166

role of magnetic resonance imaging (MRI) in the depiction of carpal bone injuries is beautifully illustrated by coronal images subsequently obtained. However, in cases that may be more subtle, differentiation of fractures from bone bruising may not be possible using this modality. Therefore, as always when bone MRI is performed, its findings should be considered in tandem with those of conventional radiography in order that the limitations of MRI are minimized.

Pisiform Again, falls on the outstretched hand are often the offending mechanism of injury when damage to the pisiform bone occurs. Patterns of bony injury commonly include transverse or longitudinal body fractures (Fig 4), comminuted fractures, or avulsion fractures.8

Trapezium or Trapezoid Fractures of these carpal bones usually result from direct trauma and may be quite difficult to diagnose. This diagnosis may be suggested by positive radioisotope scintigraphy,9 the final diagnosis being made with cross-sectional imaging, be it either CT or MRI. The coronal reconstructed CT image provided in Fig 5 shows a fracture of the trapezium, not initially appreciated on conventional radiography. Ongoing patient discomfort and clinical tenderness, combined with a positive radioisotope bone scan, prompted further evaluation with CT. This example illustrates the superior specificity of CT to these other imaging modalities in the presence of subtle cortical breach, with radiography and scintigraphy often showing only secondary effects, ie, soft-tissue edema or bone bruising. Curr Probl Diagn Radiol, July/August 2007

FIG 4. Frontal conventional radiograph of the left wrist illustrating a linear, longitudinal pisiform fracture (arrow) in a 29-year-old male patient post-FOOSH.

FIG 6. Undisplaced fracture of the trapezoid (arrow) as seen on sagittal reconstructions from a multislice CT examination on a 50-yearold male patient after blunt trauma to the left wrist.

of high-quality thin-slice imaging with reconstruction and evaluation in a number of planes, depending on the carpal bone being interrogated. Indeed, fracture of either the trapezium or the trapezoid bone is not uncommonly accompanied by fracture of the other carpal bone, given the proximity and similar articular relationships of each of these bones (Fig 7).

Capitate

FIG 5. Coronal CT reconstructed image of a fractured distal aspect of the right trapezium (arrow) in a 43-year-old male post forced dorsiflexion of the index finger, not appreciable on initial conventional radiography.

Being relatively rare and often unappreciable on conventional radiography, fractures of the trapezoid bone may go undiagnosed for quite some time. Fig 6, a sagittal CT reconstructed image, demonstrates such an undisplaced fracture. Indeed, even in retrospect, this fracture was extremely difficult to appreciate on the axial source images. This illustrates the importance Curr Probl Diagn Radiol, July/August 2007

The central location of this carpal bone results in its relative protection from direct trauma. In many cases, when fractures of this bone occur, they do so in the presence of concomitant ligamentous or adjacent bony injury. Despite this, isolated capitate fractures such as that seen in Fig 8 are not rare, estimated to represent up to 15% of cases of carpal fracture, and may be difficult to diagnose with standard conventional radiographs, not uncommonly requiring further imaging in the clinical setting of ongoing pain and tenderness to establish a diagnosis. The well-documented scaphocapitate syndrome may alternatively occur, where a scaphoid waist fracture and a proximal capitate fracture occur in tandem.10 Conventional radiography is usually sufficient to diagnose such injuries.

Hamate Direct blows to this bone are responsible for the vast majority of cases, usually due to leverage of a 167

FIG 7. Concomitant fractures of both the trapezium and the trapezoid bones with associated edema (arrows) seen on coronal proton density (A) and T2-weighted axial fat-saturated (B) MRI images from a 58-year-old female patient with recent history of FOOSH.

FIG 8. Transverse fracture of the capitate bone (arrow) with associated bone bruising confined mainly to the distal bony fragment on T1-weighted coronal MRI. This 53-year-old female patient gave a recent history of rotational-type blunt trauma to the wrist joint.

solid structure (eg, tennis racquet) against its hook. Most fractures involve the volar aspect of the bone with resultant direct tenderness over this area, which is usually straightforward to localize clinically.11 However, given the superimposition of bony structures in the region of the hamate bone, namely the body and hook of hamate, fractures of this structure are often quite difficult to appreciate on conventional wrist imaging. While carpal tunnel views may be diagnostic, it is often the case that this projection not be requested. As a result, a diagnosis of hamate hook fracture is 168

FIG 9. T1-weighted coronal MRI image from a 38-year-old male tennis player whose racket struck a hard surface, showing a resultant fracture of the base of the hook of hamate (arrow).

often made given the presence of bone bruising on MRI in the distribution illustrated in Fig 9.

Carpal Dislocation/Instability Carpal bone dislocation is usually the result of extreme flexion or extension injuries of the wrist joint. The pattern of injury so produced depends on the direction and intensity of the acting force or the position of the hand in relation to the radius at the time of impact. Central to the prevention of such injuries is the inherent stability of the capitate-lunate articulation. Curr Probl Diagn Radiol, July/August 2007

FIG 10. (A and B) T2-weighted fat-saturated coronal images showing two examples of TFCC disruption (arrows), both in male patients after sport-related impacts.

As stated earlier, maintenance of normal carpal integrity relies heavily on the strength of the ligamentous network, including the interosseous, volar, and dorsal ligaments and the triangular fibrocartilage complex (TFCC). The dorsal ligamentous structures are weaker than the volar ligaments, resulting in a higher incidence of dorsal dislocation. In contrast to specific carpal bone fractures, some of which have specific modes of injury, almost all carpal dislocations occur as a sequela of FOOSH. In many cases, fracture-dislocation, particularly trans-scaphoid perilunate dislocation, results as opposed to uncomplicated carpal dislocation.

Triangular Fibrocartilage Complex This triangular-shaped structure consists of articular disk (fibrocartilage), meniscus homologue (lunocarpal), the ulnocarpal ligament, dorsal and volar radioulnar ligaments, and the extensor carpi ulnaris sheath. It originates from firm attachments on the medial border of the distal radius and inserts into the base of the ulnar styloid, being thicker on the ulnar apect than the radial aspect and separating the radiocarpal from the distal radio-ulnar joint (DRUJ). Notably, only the peripheral 15 to 20% of the TFCC has a blood supply with the central disk being avascular. Acting as the main stabilizer of the DRUJ, this structure also contributes to ulnocarpal stability. In many cases, radiographs show no associated bony abnormality when TFCC injury is present, secondary features being soft-tissue swelling only. However, when present, avulsion of the ulnar styloid, scaphoid fracture, distal radius fracture, or volar instability patterns are the Curr Probl Diagn Radiol, July/August 2007

FIG 11. Conventional arthrographic (A) and coronal STIR-weighted (B) MRI images showing the presence of a breach in the integrity of the TFCC and disruption of the distal radio-ulnar joint (arrows), the MRI images correlating extremely well with appearances on conventional arthrography.

more likely accompanying abnormalities. Ulnar variance may also be a feature.12 Diagnosis of TFCC disruption is often reliant on the soft-tissue resolution of MRI as illustrated in Fig 10, which shows complete transection of the TFCC with associated surrounding edema. Another such case is illustrated in Fig 11, with associated compromise of the DRUJ.

Perilunate Dislocation A number of recognized patterns of carpal dislocation have been described. Of these, perhaps the most commonly encountered is perilunate dislocation. In this entity, the lunate maintains its normal anatomical articulation with the distal radial surface. However, dorsal ligamentous disruption allows dorsal displacement of the distal carpal row and digits. This type of injury characteristically results in disruption of the normally smooth carpal lines on the frontal view, with the impression of “crowding.” The lateral view is confirmatory.13 The frontal and lateral conventional radiographs of the wrist, illustrated by Fig 12, show a trans-scaphoid perilunate dislocation with an associated displaced fracture of the triquetral bone. It is not uncommon for devastating injuries such as those resulting in perilunate dislocation to be associated with fractures to adjacent, at-risk, carpal bones as in this case.

Lunate Dislocation A less commonly encountered phenomenon, lunate dislocation, results from volar displacement of the lunate, with maintenance of the linear relation169

FIG 12. Frontal (A) and lateral (B) radiographs of the wrist illustrate trans-scaphoid perilunate dislocation with an associated displaced fracture of the triquetral bone (arrow in A) in a 24-year-old male patient after FOOSH. The lunate bone is outlined in white, and the scaphoid fracture is indicated by the arrow (B).

FIG 13. Conventional frontal (A) and lateral (B) radiographs from a female patient with lunate dislocation. The margins of the lunate bone are outlined, the arrow indicating abnormal articulation of the capitate bone with the radial articular surface.

ship between the radius and distal carpal row. A triangular-shaped lunate on frontal views is suggestive but, as is the case with perilunate dislocation, the lateral view leaves little doubt in most cases (Fig 13).

Scapholunate Dissociation Also known as the “Terry Thomas Sign” after a UK comedian whose frontal dentition was unusually distracted, scapholunate dislocation results from 170

disruption of the scapholunate ligaments, with resultant increased distance and instability of the proximal carpal row. Rotational scaphoid dislocation may result. This diagnosis may be suggested by a scapholunate distance of 4 mm or greater, although this distance has a poor specificity for this injury. Radiographs obtained in the “clenched fist” position may be of value in improving specificity, with resultant increased scapho-lunate distance of up to 8 mm being visualized. A scapholunate angle Curr Probl Diagn Radiol, July/August 2007

FIG 14. (A-D) Fluoroscopic images illustrating significant divergence of the scaphoid and lunate on ulnar deviation in scapholunate dissociation (arrows in C and D), in contrast to that seen on the contralateral normal side (arrows in A and B).

FIG 15. Unremarkable conventional radiograph (A), with correlating radio-isotope scintigram (B) and T2-weighted coronal (C) images of the left wrist in scapho-lunate ligament tear. The arrows indicate regions of increased radiotracer uptake on scintigraphy as well as the location of the tear on MRI examination.

in excess of 60° on lateral views is also suggestive.14 The value of fluoroscopy in the evaluation of suspected scapho-lunate dissociation should also not be underestimated, as depicted in Fig 14. Note significant divergence of these carpal bones on ulnar deviation at the wrist joint (Fig 14C and D), in contrast to that seen on the contralateral normal side Curr Probl Diagn Radiol, July/August 2007

(Fig 14A and B). In the example provided in Fig 15, a case of scapho-lunate ligament tear, the superb soft-tissue resolution of MRI will often provide a correct diagnosis when other modalities reveal equivocal or nonspecific findings, and in the correct setting of ongoing carpal pain or discomfort, a low threshold should be employed to perform this examination. 171

FIG 17. Lateral (A) and frontal (B) conventional radiographs in a case of nonunion of a scaphoid fracture (arrow) due to Herbert screw displacement in a 29-year-old male, initially treated 4 years previously after blunt trauma to the dorsiflexed left hand. FIG 16. VISI, or volar intercalated segment instability, as seen on conventional lateral radiograph in a 27-year-old male patient postFOOSH. The arrows indicate the planes of the capitate and lunate bones.

Lunotriquetral Dissociation Lunotriquetral dissociation is often diagnosed on clinical grounds, as radiographs in the majority of patients are normal. However, even minimal increased lunotriquetral motion may result in considerable patient morbidity. On occasion, a volar instability pattern (discussed below) may be the only suggestive evidence, although the presence of a “Ring Sign,” ie, the scaphoid tubercle being seen in profile due to the flexed position of the scaphoid, on frontal views is supportive.15 Arthrography is the diagnostic method of choice, delineating even the smallest of ligamentous tears.

Carpal Instability Patterns Traumatic episodes, particularly if repetitive, may result in ligamentous laxity rather than acute ligamentous disruption. This may give rise to one of a number of recognized instability patterns, several of which are considered. As stated earlier, the integrity of the carpus relies heavily on the capitate-lunate articulation. Carpal instability patterns result, in the majority of cases, from loss of the normal linear relationship of these bony structures, with secondary carpal “shortening.” 172

The most commonly encountered instability pattern is that of dorsiflexed intercalated segment instability pattern, in which the lunate dorsiflexes on the radial articular surface. A compensatory volarflexion of the capitate occurs. This pattern has a significant association with scaphoid fracture or dislocation and often results from unrecognized scaphoid injury. This entity may be diagnosed when a lunate angulation of greater than 10° is present on the lateral view. It is also characterized by a scapholunate angle "70°.16 Volar intercalated segment instability is the term given to the opposite scenario, with volar flexion of the lunate relative to the radius with secondary dorsal angulation of the capitate, as illustrated in Fig 16. This abnormality is characterized by a scapholunate angle #30°.17 Less frequently encountered instability patterns include ulnar translocation, in which case the lunate translocates in an ulnar direction, a scenario commonly seen in rheumatoid arthritis patients,18 and nondissociative carpal instability, where the internal articular relationships of the proximal and distal carpal rows is maintained, but that between these two rows is disrupted, eg, mid-carpal instability.19

Complications ●

Persistent pain and weakness may result from continuing ligamentous instability. Curr Probl Diagn Radiol, July/August 2007

FIG 18. Conventional radiograph (A), T1-weighted (B), and T2-weighted fat-saturated coronal (C) MRI images of illustrating posttraumatic Kienbock’s disease (arrows) in a 42-year-old female patient.

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Persistent physical deformity, particularly in the case of combined fracture dislocations. Fracture malunion, delayed union, or nonunion (Fig 17). Secondary osteoarthritis (Fig 17). Carpal tunnel syndrome.20 Numbness, tingling, intrinsic muscular atrophy, and hand weakness may result from direct pressure effect of a displaced carpal bone, bony fragment, or edematous tissue on the median nerve within the carpal tunnel, with resultant entrapment. Avascular necrosis. Particularly common involving the scaphoid bone, due to the nature of its blood supply, this entity may potentially affect any of the carpal bones. Kienbock’s disease,6 or lunatomalacia, is the name given to collapse of the lunate due to vascular insufficiency and secondary avascular necrosis. It may result from a single or multiple repetitive, often subclinical, traumatic episodes. It is strongly associated with a negative ulnar variance, a presumed predisposing factor. Damage resulting from trauma may not necessarily be appreciated at the initial time of injury, as in the case illustrated in Fig 18, a patient who failed to seek medical advice following a fall on the outstretched hand. However, failure of this discomfort to abate resulted in repeat presentation for conventional radiography, which revealed increased sclerotic change of the lunate bone, typical of Kienbock’s disease. These conventional radiograph findings were subsequently confirmed at MRI, by the presence of abnormally low signal intensity within this bone.

Curr Probl Diagn Radiol, July/August 2007

FIG 19. Coronal STIR-weighted image of the wrist illustrating widespread carpal hyperintensity involving numerous carpal bones (arrows) in a case of reflex sympathetic dystrophy. This 55-year-old female patient gave a remote history of wrist trauma.

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Reflex sympathetic dystrophy.21 This is an incompletely understood condition resulting in pain that is nonanatomic and disproportionate to the inciting event or expected healing response. It is characterized by diffuse pain, associated swelling, trophic changes, and vasomotor disturbance. It may accompany a fracture, but definite bony injury is not a requirement to the development of reflex sympathetic dystrophy (Sudek’s atrophy). Conventional radiography is rarely of value, only showing osteoporosis on occasion. Radionuclide 173

FIG 20. Conventional oblique (A), frontal (B), and lateral (C) radiographs of the right wrist illustrating the coexistent presence of fractures of the scaphoid, hamate, and triquetral bones (arrows) in this patient with “generalized wrist pain” following direct blunt trauma to the hand.

scintigraphy is the only accepted imaging technique and tends to show increased tracer uptake in the involved areas on delayed imaging with hyperemia and soft-tissue uptake on the arterial and blood-pool images, respectively. MRI has also shown promise, illustrating widespread carpal hyperintensity on T2-weighted images corresponding with edematous change (Fig 19).

Investigation In a large proportion of cases, posttraumatic carpal sequelae can readily and confidently be diagnosed on conventional radiography alone. In addition to standard wrist views, dedicated coned scaphoid views are of considerable value in the exclusion of a fracture of this particular bony structure. However, diagnostic dilemmas arise in the situation of ongoing, persistent, or worsening pain without apparent radiographic abnormality. Conventional radiography, radio-isotope scintigraphy, CT, and MRI all have potential and valuable roles in the evaluation of such patients and the relevant strengths and weaknesses of each shall be considered in turn.

Conventional Radiography While often not initially appreciable on basic radiography, carpal fractures may become more conspicuous with time. The value of delayed imaging, usually performed at 10 to 14 days after the initial traumatic insult, and after a period of immobilization, cannot be overstressed. Fracture marginal sclerosis and early callus formation increases the sensitivity of this imaging technique. All such images should be obtained out of plaster, thus maximizing sensitivity. Accessory 174

views, coned views, and tomographic evaluation may also aid the diagnostic process. This technique is limited, however, by the presence of multiple overlapping bony structures and persistent basic radiologic evaluation may prove futile in the setting of clinically suspected yet radiologically unconfirmed carpal fracture. False-positive results, or pseudofractures, may also result from prominent trabecular patterns. In equivocal cases, a low threshold should be maintained for further evaluation with more advanced investigative techniques.22

Bone Scintigraphy Based on the fact that bone with an increased metabolic “turnover,” as is the case with fracture, will have a focal intense uptake of radio-isotope-labeled phosphate, this technique may be of considerable value in the exclusion of clinically suspected carpal fracture. Indeed, the value of this investigation lies mainly in its high sensitivity, a negative result virtually excluding a carpal fracture. False-positive results, however, may result from increased uptake in regions of bone contusion or incomplete cortical fracture.23

Computed Tomography Images are acquired in 1- to 2-mm sections and are subsequently reconstructed in a variety of planes depending on the clinically suspected injured carpal bone. While unable to adequately assess soft-tissue injuries and bone contusions, CT has excellent sensitivity in the detection of subtle, incomplete fractures.24 Pseudofractures resulting from overlapping bony outlines on conventional radiography may also be confidently excluded. CT also has the added value of providing important preoperative information for Curr Probl Diagn Radiol, July/August 2007

cases in whom surgical intervention is being contemplated.

MRI MRI is rapidly becoming incorporated into the diagnostic algorithm for suspected carpal injury, given its exquisite soft-tissue resolution and high sensitivity to the presence of soft-tissue and bony pathology. T2-weighted sequences, particularly short-tau inversion recovery (STIR) techniques, allow confident assessment for the presence of bony or soft-tissue edema. However, this high sensitivity for the presence of edema may result in overdiagnosis of the presence of fracture, bony contusion having similar appearances.25

Conclusions Carpal injuries, be they bony contusions, fractures, or soft-tissue trauma with secondary instability, account for a significant proportion of hospital emergency room attendances and are often the source of much clinical–radiological consternation. Knowledge of the spectrum of potential injuries aids the assessing clinician in the evaluation and successful management of such injuries. Understanding of the complex arrangement of these structures aids one in the detection of concomitant injuries, as fracture of one carpal bone should be taken as an indication of significant trauma with potential injury elsewhere. A detailed search for concomitant fractures should follow, with often subsequent further imaging in the form of bone scintigraphy, CT, or MRI being required to rule out the presence of synchronous bony injury or ligamentous tear. The carpal region is certainly one area in particular in which the phrase “satisfaction of search” certainly applies. This is illustrated in Fig 20; coexistent fractures of the scaphoid, hamate, and triquetral bones were present in a patient complaining of “generalized wrist pain” following trauma.

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