Imaging of the Wrist and Hand




Imaging evaluation of hand and wrist injuries in the athlete begins with conventional radiographs. Radiographs are excellent for detecting osseous injuries or malalignment in osseous structures as a result of ligament disruption. A standard wrist series includes posteroanterior (PA), lateral, and oblique views ( Fig. 72-1 ).




FIGURE 72-1


Conventional radiographs of the wrist. A, Posteroanterior view. B, Lateral view. C, Oblique view.


A standard PA view is obtained with the shoulder abducted, the elbow flexed 90 degrees, and the forearm in a neutral position ( Fig. 72-1, A ). Evaluation begins with examination of the distal radius and ulna. Any cortical disruption in a skeletally mature patient may be indicative of fracture. Standard parameters to be checked include radial inclination, radial height, and ulnar variance. Radial inclination describes the angulation of the distal radius articular surface relative to the long axis of the radius, typically 23 degrees (range, 16 to 30 degrees). Radial height is the distance measured between two parallel lines perpendicular to the radial shaft, one drawn across the tip of the radial styloid and the second across the distal ulna surface. The radial height averages 11 mm (range, 10 to 13 mm). Deviations of these indices suggest an underlying abnormality.


Ulnar variance is the relative difference in height at the distal ulna and radius articular surfaces. When the wrist is at ulnar neutral variance, the distal ulna and distal radius articulations form a contiguous line where they meet. Deviation of the distal ulna head distal to the adjacent distal radius articulation is considered positive ulnar variance, and conversely, proximal migration of the distal ulna head relative to the distal radius articulation is considered negative ulnar variance. Pronation or supination of the forearm will alter ulnar variance, and therefore the image must be obtained with the forearm in the neutral position for accuracy and compared with the contralateral wrist.


It is important to note the relationship of the distal radioulnar joint (DRUJ). Diastasis between the radius and ulna at the DRUJ can be pathologic. The eight carpal bones have unusual shapes, and overlap makes assessment challenging. The carpal bones form three contiguous, smooth, parallel arcs along the proximal articular margins of the proximal carpal row, the distal articular margins of the proximal carpal row, and the proximal articular margins of the distal carpal row. Any disruption of these “arcs of Gilula” suggests disruption of carpal alignment. Finally, each intercarpal and carpometacarpal joint space should be scrutinized individually for congruency.


On a true lateral radiograph of the wrist ( Fig. 72-1, B ) in neutral rotation, the axis of the radius, lunate, capitate, and third metacarpal should be collinear. On an appropriately obtained lateral wrist image, the volar edge of the pisiform lies between the distal pole of the scaphoid and the palmar aspect of the capitate head. The scapholunate angle is subtended by a line parallel to the long axis of the lunate and a line parallel to the long axis of the scaphoid. Normally, it measures 45 degrees (range, 30 to 60 degrees). Palmer tilt, which measures the slope of the distal radius articular surface relative to a line perpendicular to the long axis of the radius, is usually 0 to 20 degrees, with a mean of 12 degrees. Any degree of dorsal tilt is considered abnormal.


A standard series of radiographs for evaluation of the hand also includes PA, lateral, and oblique views. If an injury or problem is truly isolated to the thumb or a digit, individual radiographs of these digits are best. An appropriate lateral hand view is obtained with the fingers spread in a cascade to profile the phalanges and interphalangeal joints. Hand injuries are often subtle, and additional rotated views are often necessary to evaluate the metacarpophalangeal and carpometacarpal joints in particular.


Any patient presenting with pain at rest or a “mass” at the wrist or hand is first evaluated with conventional radiographs. Occasionally, radiographs are pathognomonic for entities such as Kienböck disease or Madelung deformity. Atypical imaging findings, such as a calcified soft tissue mass or lytic osseous lesion, may prompt further evaluation by an upper extremity or oncologic orthopaedic specialist.


Many injuries of the wrist and hand involve a combination of osseous and soft tissue structures. When conventional radiographs are unrevealing or provide incomplete information, the choice of additional studies is guided by the history and physical examination. These additional studies may include computed tomography (CT), magnetic resonance imaging (MRI), magnetic resonance arthrography, live fluoroscopy, and a bone scan. Some relevant injuries and their classic imaging findings are highlighted in this chapter to aid the general orthopaedic surgeon or sports medicine specialist.


Wrist Injuries


Distal Radius Fractures


Standard views of the wrist are mandatory and typically adequate to discern extraarticular and simple intraarticular fracture patterns. Obtaining the same views with traction takes advantage of ligamentotaxis that can better align fracture fragments and decompress areas of impaction and/or comminution. Although some debate has ensued about “normal” radiographic parameters after reduction of a distal radius fracture depending on the characteristics of the given patient, the American Association of Orthopaedic Surgeons has provided recommendations in a recent clinical practice guideline. Operative fixation is suggested for fractures with more than 3 mm of radial shortening, 10 degrees of dorsal tilt, and 2 mm of intraarticular incongruity. CT scans are sometimes used to better characterize complex intraarticular fracture patterns, especially when surgery is planned and the best approach for internal fixation is equivocal. Katz et al. established that CT increased interobserver reliability in the management of complex distal radius fractures. MRI is rarely necessary for distal radius fracture management, although it may be helpful in assessing ligamentous injuries often associated with distal radius fracture.


Carpal Fractures


Scaphoid Fracture


In addition to the standard wrist series, special views may be necessary to identify scaphoid fractures. The scaphoid or “navicular” view, obtained with the wrist partially extended and in maximal ulnar deviation, and the 45-degree semipronated radiographic views are best for scrutinizing the scaphoid in profile ( Fig. 72-2 ). When these initial radiographs are unrevealing and a high clinical suspicion for occult fracture exists, adjunctive studies such as MRI, CT, or a bone scan are preferred for earlier detection of a scaphoid fracture. This early detection is critical in athletes because treatment decisions are often dictated by how quickly they can return to sport. Multiple studies have shown that MRI may be the best modality for the early detection of a scaphoid fracture. A metaanalysis by Yin et al., including 41 different studies, with a cumulative total of 1826 patients, showed a pooled sensitivity and specificity of 97% and 89%, respectively, for bone scintigraphy; 93% and 99%, respectively, for CT; and 96% and 99%, respectively, for MRI. On T1-weighted images, an occult fracture appears as a distinct low-signal-intensity line surrounded by high-signal marrow fat ( Fig. 72-3 ). Fat-suppressed T2-weighted images show high-signal marrow edema surrounding the fracture line.




FIGURE 72-2


Scaphoid fractures. From left to right, radiographs show a distal scaphoid tuberosity fracture, a scaphoid waist fracture, and a proximal pole fracture. The fracture location has implications for healing and treatment options.



FIGURE 72-3


An occult scaphoid fracture. A, This radiograph was read as normal. No obvious fracture line is visible. B, Because of clinical suspicion, a magnetic resonance imaging scan was obtained, which showed a scaphoid waist fracture.


Trapezium Fracture


Displaced fractures of the trapezium body are readily seen on conventional radiographs of the wrist; however, more subtle fractures of the trapezial ridge can be missed. Specific radiographs of the thumb, including dedicated PA, lateral, and Roberts views, are better for detecting these injuries and determining displacement. The Roberts view is essentially a true anteroposterior view of the first metacarpophalangeal joint taken with the hand in hyperpronation, with the dorsum of the thumb resting on the radiograph cassette. A carpal tunnel view may also help identify fractures of the trapezial ridge. For additional osseous detail or surgical planning, a CT scan can be helpful ( Fig. 72-4 ).




FIGURE 72-4


A trapezium fracture. A, A vertical fracture of the trapezium with intraarticular involvement both proximally and distally. B, Computed tomography can help identify main fracture fragments for surgical plans. Oblique (C) and lateral (D) radiographic views of the wrist after open reduction and internal fixation of the fracture to restore articular congruity. An additional thumb metacarpal base fracture was also stabilized.


Capitate Fracture


A displaced fracture of the capitate typically results in inversion of the proximal capitate fragment that is easy to detect on conventional radiographs of the wrist. Additional views that are helpful in visualizing the fracture include the semipronated 45-degree oblique view and a clenched-fist PA view. A nondisplaced capitate fracture may be difficult to detect with conventional radiographs. Other modalities such as CT and MRI are indicated if conventional radiographs are negative and there is clinical suspicion of an injury at this location. These injuries occur more frequently as part of a greater arc perilunate dislocation than in isolation.


Hamate Fracture


Routine radiographic examination is typically inadequate for hamate fracture detection. A carpal tunnel view or a semisupinated oblique view makes it easier to visualize the hamate profile and its volarly projecting hook. If the clinician has a high index of suspicion for a hamate injury in spite of results of normal conventional radiographs, then a CT scan is the typical test of choice. In cases of chronic hamate hook nonunion, MRI may reveal flexor tendon injury within the carpal canal or extrinsic compression on the ulnar nerve as it travels through Guyon’s canal.


Perilunate Dislocation


For the astute observer, standard wrist views are adequate for recognizing perilunate dislocations. The PA view alone, however, may look deceptively normal, and up to 25% of these injuries are missed at initial presentation. On the lateral view, the capitate is dislocated dorsal to the lunate, which may either remain in its fossa at the distal radius (Mayfield stage III) or dislocate volarly (Mayfield stage IV) ( Fig. 72-5 ). Because of the difficulty in achieving a stable closed reduction and the high incidence of acute carpal tunnel syndrome, clinical urgency typically precludes additional imaging studies. These injuries require definitive surgical treatment without exception.




FIGURE 72-5


Posteroanterior ( left ) and lateral ( right ) radiographs of a perilunate dislocation. Notice the difficulty of assessing the dislocation on the posteroanterior view alone. On the lateral radiograph, the lunate is seen to be completely dislocated.


Ulnar Impaction Syndrome


Ulnar impaction syndrome describes chronic abutment of the lunate and/or triquetrum with a prominent distal ulna articulation. Ulnar positive variance is a common finding, along with subchondral sclerosis and/or cyst formation at the distal ulna and proximal carpal row. Upon MRI evaluation, ulnar impaction syndrome is characterized by a combination of degenerative central triangular fibrocartilage complex (TFCC) perforation, articular cartilage thinning, possible lunotriquetral ligament tear, and focal signal alteration at the impacted areas of the carpus and distal ulna. The increased signal intensity within the lunate on T2-weighted images is focal rather than diffuse, which helps distinguish this process from Kienböck disease.


Kienböck Disease


Kienböck disease is idiopathic osteonecrosis of the lunate. It is often associated with negative ulnar variance. Progression of the disease is characterized by imaging findings. In the earliest stage of the disease, conventional radiographs are normal, but T1-weighted MRI sequences reveal diffuse low-signal intensity throughout the lunate. T2-weighted MRI sequences correlate with prognosis, with increased signal intensity directly proportional to lunate vascularization. In the second stage, sclerosis becomes apparent on conventional radiographs. By the third stage, the lunate breaks into fragments and collapses, and carpal malalignment follows. In the fourth stage, pancarpal arthritis is evident. Early diagnosis by MRI is critical because early surgical intervention may slow the progression of disease and prevent lunate collapse with subsequent arthritis.


Intrinsic Carpal Ligament Injury


The scapholunate and lunotriquetral ligaments are the most important intrinsic ligaments and the most susceptible to traumatic injury. For scapholunate dissociation, notable findings on the standard PA view include foreshortening of the scaphoid, widening of the scapholunate interval (normally 2 to 3 mm), and a triangular appearance of the lunate because of its extended posture. The PA view may reveal a “cortical ring sign,” where the abnormally flexed scaphoid creates superimposition of its distal pole and waist. Lunotriquetral ligament disruption may produce a widened lunotriquetral interval on a PA view, although this finding is more infrequent than with the corresponding pathology at the scapholunate interval. On a lateral wrist radiograph, a scapholunate angle of more than 60 degrees portends dorsal intercalated segmental instability and scapholunate dissociation ( Fig. 72-6 ). Conversely, a scapholunate angle of less than 30 degrees suggests volar intercalated segmental instability and possible lunotriquetral ligament disruption. The relative position of the lunate in the sagittal plane, with the wrist at neutral, predicts the instability pattern ( Fig. 72-7 ). Additional specialized radiographic views for suspected scapholunate dissociation include the semipronated 45-degree oblique view, a clenched-fist anteroposterior view, and a PA view in ulnar deviation with the beam centered on the scaphoid. Ulnar deviation also stresses the scapholunate ligament and accentuates scapholunate widening. Abnormal carpal kinematics are often elicited only under physiologic loading conditions, and pathology may be missed on static radiographs. Dynamic fluoroscopy is an adjunctive test that can show asynchronous carpal motion during certain wrist positions or when stress is applied. Compared with wrist arthroscopy, cineradiography has a specificity and sensitivity of 95% and 86%, respectively, for detecting scapholunate ligament tears.


Feb 25, 2019 | Posted by in SPORT MEDICINE | Comments Off on Imaging of the Wrist and Hand
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