Diagnostic imaging of the hand and wrist

Evaluation of the hand

The three basic radiographs to evaluate the hand are: posteroanterior (PA), oblique, and true lateral views. The radiographs should be performed in a standardized fashion to allow proper evaluation ( Figs. 3.1 & 3.2 ). Specialized views are required to assess specific areas not well seen in the above views. The PA hand view provides a useful overview of the skeletal structure of the hand. Fractures, osseous tumors, and even soft-tissue masses ( Fig. 3.3 ) can be seen on this view. The oblique view of the hand is useful to assess the metacarpals, as a true lateral view of the hand will lead to an overlapping of the second to fifth metacarpals. In the common boxer's or fifth metacarpal neck fracture, this view allows an assessment of the amount of angulation of the fracture.

In hand radiographs, begin by assessing the overall alignment of the metacarpals and phalanges. The individual bones should then be evaluated in terms of cortical shape and integrity, as well as bony quality. Fractures are usually easy to detect, although a careful review is necessary in the case of undisplaced or minimally displaced fractures. Osseous tumors are identified by an area of different lucency in the bone. There may be changes in the outline of the bone. Enchondromas are common benign bony tumors in the hand. They can result in pathological fractures, so an assessment of the bone for such pathology should be done, particularly if the trauma resulting in the injury is trivial ( Fig. 3.4 ). Osteomyelitis typically occurs in the hand following open injuries ( Fig. 3.5 ).

The joints should then be assessed, starting from the carpometacarpal joints (CMCJs) and working distally. The CMCJs may be dislocated following injury. These injuries are uncommon but are difficult to diagnose. In a normal hand X-ray the second to fifth CMCJs should be clearly visible on the PA view ( Fig. 3.6 ). The loss of these features in the second to fifth CMCJs is usually due to a fracture dislocation of one or more of the CMCJs. However, an improperly performed hand radiograph can also give this impression. Fisher et al . described a systematic approach to evaluating the PA view of the hand for dislocations of the fourth and fifth CMCJs. In subluxation of the fifth CMCJ, the base of the fifth metacarpal is usually offset ulnarly compared to the hamate ( Fig. 3.7 ). Several views have been suggested to confirm this diagnosis. The true lateral of the hand provides a useful way to assess the CMCJ for any signs of dislocation and oblique views may also be helpful ; if the diagnosis is still uncertain, a CT scan of the hand including the CMCJs will confirm the diagnosis. The more distal joints are then evaluated, from the metacarpophalangeal joints to the proximal interphalangeal joints and distal interphalangeal joints. A normal joint should be completely congruent with a visible joint space.

Osteoarthritis commonly affects the interphalangeal joints and thumb CMCJs. It is often demonstrable on radiographs by narrowing of the joint space, subchondral sclerosis, osteophytes, and deformity ( Fig. 3.8 ).

Special views in the hand

( Box 3.1 )A true lateral radiograph of the finger is needed to complete an assessment of the digit. Hand radiographs alone are insufficient for assessment. This is because the oblique view of the hand does not provide an adequate lateral profile of the digit and interphalangeal joint spaces to supplement the PA view. With only a PA view, subtle fractures, fracture displacement, or joint subluxation of the fingers may not be apparent. Metacarpal head fractures may also be difficult to assess and the Brewerton view will give additional information to the standard hand radiographs.

To assess the thumb, specialized views are also necessary as the thumb lies in an oblique plane relative to the other digits in the usual hand radiograph. A true PA and lateral view of the thumb is obtained to allow proper radiographic assessment of the thumb. One common condition in the thumb for which radiographs are performed is that of basal joint or trapeziometacarpal joint (TMCJ) arthritis ( Fig. 3.9 ). This condition is graded radiologically using the Eaton classification. The irregular saddle shape of the trapezium makes visualization of the bone difficult, and the Betts view will allow all four articulations of the trapezium to be visible without overlap ( Fig. 3.10 ).

The ulnar collateral ligament of the thumb metacarpophalangeal joint is commonly injured in forceful thumb abduction. Less commonly the radial collateral ligament may also be injured. Lateral stress application during the posteroanterior thumb radiograph can be helpful to assess if the ligament injuries are complete or partial. Ultrasonography and MRI are alternatives to assess this injury.

Pediatric hand radiographs

Evaluation of the pediatric hand, especially after injury, is often more difficult than in adults. All carpal bones and epiphyses in the hand lack ossification in the newborn. The ossification centers then appear in a well-recognized sequence, as detailed in Table 3.1 . The staggered ossification of the various carpal bones ( Fig. 3.11 ) and the presence of the growth plate may confuse the examiner as to whether a fracture is present or not.

A misdiagnosis rate of 8% for pediatric hand fractures was found in one study. There are several reasons for this. Clinical evaluation in children is more difficult, the more so the younger the child. It may not be possible to localize the site of the problem clearly, e.g., the site of injury following trauma. Proper standardized views may also be difficult to obtain. Other reasons for misdiagnosis include missing additional fractures and using an X-ray that was obscured by dressings. When the clinical suspicion remains high and the films obtained are inadequate, the radiograph should be repeated, either the same day or at another time when the patient is more cooperative. Similar views taken of the opposite uninjured limb are also helpful for evaluation.

Growth plate-related injuries are common in children. These injuries can be classified according to the system described by Salter and Harris ( Fig. 3.12 ). The Salter–Harris type II fracture injury is the most common type of growth plate injury seen in the hand.

Wrist evaluation

A properly performed set of orthogonal wrist radiographs forms the basis of an effective evaluation of the wrist. This is especially important when indices are being measured. The wrist has numerous asymmetrically arranged bones, so a methodical assessment of the bones, joints, and overall alignment of the wrist is necessary.

Obtaining proper views for wrist radiographs (see Fig. 3.1 ; Fig. 3.13 ; see Fig. 3.18 ) requires careful positioning which may be difficult to achieve in patients with pain or limitations in motion of the affected upper limb ( Box 3.2 ).

The wrist radiograph is first evaluated by checking the overall alignment of the bones of the wrist, starting with the distal radius and ulna, progressing to the carpal bones and metacarpal bases. Gilula described three smooth arcs made by the articular surfaces of the proximal and distal carpal row bones in a normal wrist PA radiograph ( Fig. 3.14 ). A loss of the normal contour usually indicates a disruption in the normal arrangement of these carpal bones. A common cause of this is a perilunate dislocation ( Fig. 3.15 ). Lunotriquetral (LT) dissociation is another cause of the loss of the normal Gilula's lines. Care must be taken when interpreting these findings in an asymptomatic patient as radial or ulnar deviation of the wrist can introduce a break in the arcs.

The overall relationship between the different bones can also be assessed using two common parameters: the carpal height ratio and ulnar variance. These provide a quantitative assessment of the structural integrity of the carpal rows, and the relationship of the distal radius and ulna articular surfaces, respectively.

The carpal height ratio ( Fig. 3.16 ) gives a measure of the distance between the distal articular surface of the radius to the proximal articular surface of the third metacarpal base. A loss of this distance is seen in collapse of a carpal bone, for example Kienbock's disease (avascular necrosis [AVN] of the lunate) or in malrotation of the carpal bones, for example in rheumatoid arthritis or scapholunate (SL) dissociation. A ratio is used instead of actual dimensions to correct for variability in carpal bone sizes.

The ulnar variance provides a measure of the height difference between distal radius and ulnar articular surfaces. There are several ways to measure the ulnar variance. We prefer the technique of the perpendiculars ( Fig. 3.17 ). It is easy to perform and has been shown to have higher intra- and interobserver reliability.

A proper PA and lateral radiograph of the wrist ( Fig. 3.18 ; see Fig. 3.13 ) is the first necessary imaging for the evaluation of a suspected distal radioulnar joint (DRUJ) instability. Radiographic findings associated with this injury include widening of the DRUJ, a fracture of the ulnar styloid base, or a displaced fracture from the ulnar fovea. On the lateral view, there is loss of the normal radioulnar overlap. A comparison radiograph of the contralateral normal wrist is helpful if the findings are unclear. The application of volar or dorsal-directed stress is also helpful in cases of suspected DRUJ instability ( Fig. 3.19 ).

Scaphoid fractures are the commonest carpal fracture. The shape of the scaphoid bone does not lend itself well to evaluation by just two orthogonal views, so a “scaphoid series” of X-rays is usually done ( Fig. 3.20 and Box 3.3 ).

Fractures of the hook of the hamate are uncommon but disabling. A carpal tunnel view is helpful to diagnose this injury ( Fig. 3.21 ), although a CT scan can also provide the definitive diagnosis.

Injuries to the wrist ligaments, for example the SL ligament, can lead to carpal instability. In severe cases, this can be seen on the usual wrist views as loss of the normal relationships between the carpal bones. In SL instability, this is typically seen as a dorsal intercalated segmental instability deformity ( Fig. 3.22 ) with an increase in the SL angle, and dorsal tilt in the radiolunate angles ( Fig. 3.23 ). However, in milder forms of instability, ­application of loads and/or positioning of the wrist are necessary to bring out these dynamic changes in carpal relationships. The clenched-fist PA series of the wrist is one technique used to diagnose dynamic carpal instability ( Fig. 3.24 ).

Ulnar abutment syndrome is a common cause of ulnar-sided wrist pain. The use of a clenched-fist pronated view of the wrist enhances the ulnar variance and may demonstrate the abutment ( Fig. 3.25 ).

Wrist evaluation in distal radius fractures

Distal radius fractures are the commonest fractures encountered in the emergency room. Loss of the normal distal radius indices ( Figs. 3.26 & 3.27 ) due to fracture displacement can affect final outcome. Unstable and displaced fractures are commonly treated with plates and screws. Screws placed subchondrally offer the greatest rigidity in fixation. However, conventional wrist views do not allow accurate assessment of screw position, especially when a distal fracture line compels the surgeon to place the screws in close proximity to the radiocarpal joint. This is because standard views do not compensate for the normal anatomic tilt of the radius. Radiographs angled 22° lateral and 11° posteroanterior ( Fig. 3.28 ) enable tangential X-ray exposure to the articular surface and facilitate this assessment after fixation. With increasing using of volar plates for treatment of distal radius fractures, extensor tendon rupture from screw protrusion dorsally is a concern. Detection of dorsal screw protrusion from a lateral X-ray has a sensitivity of only 56%, and on average, protrusion of the radial-most screw can only be detected at a minimum of 6.5 mm of protrusion. Special X-ray views can be done to improve detection of screw protrusion ( Box 3.4 and Fig. 3.29 ).

Box 3.4

Additional views for assessment of dorsal screw penetration from distal radius

Supinated

This view aligns the X-ray beam to the radial side of the dorsal cortex, allowing easier detection of prominent screws in the first and second dorsal compartment.

Pronated

This view aligns the X-ray beam to the dorsal-ulnar corner of the distal radius and allow easier detection of prominent screws in the fourth extensor compartment.

Dorsal horizon view

This view is done with the wrist hyperflexed and the X-ray beam aimed along the longitudinal axis of the radius.

The availability of fluoroscopy in many clinics and operating rooms allows the dynamic assessment of many hand and wrist conditions. Smaller, lower cost, and lower radiation mini C-arms have also lowered the barrier to acquiring such facilities. The clinician can operate the C-arm to obtain the best view and view changes in the relationships of the bones “live” with motion, loading, or application of stress. Fluoroscopy is helpful for assessing carpal instability, including SL injuries ( Video 3.1 ) and midcarpal instability ( Video 3.2 ), guiding percutaneous insertion of implants, and assessing the position of implants.

Introduction

Ultrasound is widely used in hand surgery. The ultra-high frequency probes and smaller probe sizes allow higher-quality images of the hand and wrist ( Video 3.3 ). Ultrasound's safety, portability, and relatively low cost have supported wider adoption.

Beyond its accessibility and lack of radiation exposure, one additional advantage of ultrasound over other forms of advanced imaging, like CT scanning or MRI, is that it allows dynamic and real-time assessment. The addition of Doppler imaging enhances the information provided by the ultrasound study.

Ultrasound uses the acoustic properties of generated sound waves to form images. An ultrasound transducer generates the sound waves in pulses. When the transducer is applied over the surface of the part to be examined, the sound waves pass through tissues. At the junction of two tissues, an acoustic interface occurs. When the sound waves meet an acoustic interface, some of the sound wave energy is reflected, while the rest continues to be transmitted deeper. The greater the differences in material properties of the adjacent tissues, the more energy is reflected. The reflected sound wave is received in the transducer. This is then converted to an electrical signal for processing. The greater the sound reflected, the larger the amplitude of the reflected wave, and consequently, the brighter the image. The primary mode used in hand surgery is the B-mode where two dimensional images are created by simultaneous scanning the area of interest with a linear array of transducers. This provides a cross-sectional image with the horizonal and vertical directions corresponding to the real distances in tissue and the grayscale corresponding to the echo strength.