Distal Radial Fracture Imaging 

The distal radial fracture is the most common forearm fracture. It is usually caused by a fall onto an outstretched hand (FOOSH). It can also result from direct impact or axial forces. The classification of these fractures is based on distal radial angulation and displacement, intra-articular or extra-articular involvement, and associated anomalies of the ulnar or carpal bones.^{[1, 2, 3, 4]} (See the images below.)

Most distal radial fractures are diagnosed by conventional radiography. Computed tomography (CT) scanning and magnetic resonance imaging (MRI) are used to evaluate complex distal radial fractures for the assessment of associated injuries and for surgical planning.

Wrist injuries that cause pain, edema, crepitus, deformity, or ecchymosis should be evaluated for radial fractures. Missed distal radial fractures can lead to significant morbidity.

A universal classification of distal radial fractures (see Table 1, below) was proposed in 1990. This system differentiates between extra-articular and intra-articular fractures, as well as between stable and unstable fractures; it was created as a treatment-based algorithm. Classification systems are based on the following 2 principles:

• The classification should dictate the treatment.
• The classification should suggest the long-term, functional results of treatment or be correlated with these anticipated results.^{[2, 5, 6, 7, 8, 9]}

Table 1. Universal Classification of Distal Radial Fractures (Open Table in a new window)

Preferred examination

Posteroanterior (PA), lateral, and oblique radiographs of the injured forearm should be obtained.^{[10, 11, 12, 13]} Oblique views reveal intra-articular involvement that is not apparent on the other views. The semisupinated, oblique view demonstrates the dorsal facet of the lunate fossa, whereas the partially pronated, oblique PA view allows visualization of the radial styloid.

Radial height is assessed on the PA view. It is a measurement between 2 parallel lines that are perpendicular to the long axis of the radius. One line is drawn on the articular surface of the radius, and the other is drawn at the tip of the radial styloid. The normal radial height is 9.9-17.3 mm.^[14] Measurements of less than 9 mm in adults suggest the presence of comminuted or impacted fractures of the radial head. Comparison with the contralateral normal wrist is recommended if the diagnosis is unclear (see the images below).

Radial inclination is measured on the PA view; this is a measurement of the radial angle. A line is drawn along the articular surface of the radius perpendicular to the long axis of the radius, and a tangent is drawn from the radial styloid. The normal angle is 15-25º.^{[15, 16]} Angulation of the radial head also provides impaction clues (see the image below).

The volar tilt, or palmar inclination, is measured on the lateral view. A line perpendicular to the long axis of the radius is drawn, and a tangent line is drawn along the slope of the dorsal-to-palmar surface of the radius. The normal angle is 10-25º.^{[15, 16]} A negative volar tilt indicates dorsal angulation of the distal, radial articular surface (see the image below).^[17]

Ulnar variance is measured on PA radiographs. In adults, the following 3 methods are used^[14] :

• Project-a-line technique
• Method of perpendiculars
• Concentric-circle technique

Ulnar variance is described as being zero, minus, or plus. Positive (plus) or negative (minus) ulnar variance should be compared with the variance on the contralateral normal forearm.^[15] Normal ulnar variance is 9-12 mm. Note that ulnar variance does not depend on the length of the ulnar styloid but on the positioning of the forearm, as well as on the radiographic technique.

Because the distal radius and ulna can fracture and because related ligamentous or bony injuries can be occult, an evaluation of the soft tissues of the distal forearm is important. For this assessment, 2 fat planes on the lateral view and 5 fat planes on the PA view are useful.

On the lateral view, the deep fat pad of the pronator quadratus and the dorsal skin subcutaneous fat line can be seen anterior to the distal radius. The deep fat pad of the pronator quadratus forms a slight, ventral concave line. This is convexly bowed in a ventral direction or completely absent in pathologic conditions. The dorsal skin subcutaneous fat line is flat or is a dorsal concave line. It is abnormal when it is convex in the dorsal direction.

The PA view shows the thenar, hypothenar, pararadial, and paraulnar skin subcutaneous fat lines and the deep, navicular fat pad. Swelling that is not associated with an observed fracture should initiate a search for an additional abnormality.

In suspected instances of extensive soft-tissue damage, CT scanning or MRI may be used.

Plain radiographs do not show the extent of soft-tissue damage or of radioulnar and radiocarpal joint involvement.

Distal radial fractures that are not appropriately diagnosed with radiographic methods may result in increased morbidity. At minimum, PA and lateral plain radiographs are required, but oblique and other views may be warranted, depending on the patient's history and examination findings. CT scanning and MRI can be used to assess occult fractures and the extent of associated soft-tissue damage.

Beware of missed radioulnar subluxations. Radiographic findings that are minute or possibly normal variants require comparison with the contralateral normal wrist and further studies before interventional procedures are recommended.

Colles fracture

In 1813, Abraham Colles described the Colles fracture, which is reported to be the most common distal radial fracture. The injury is usually produced by a fall onto an outstretched hand (FOOSH) mechanism with the wrist in dorsiflexion. The impact produces a transverse fracture in the distal 2-3 cm of the radial articular surface. The fracture is dorsally displaced and may be comminuted. The fracture pattern is often described as a silver or dinner-fork deformity. The fracture fragments are usually impacted and comminuted along the dorsal aspect; the fracture can extend into the epiphysis to involve the distal radiocarpal joint or the distal radioulnar joint.^[18]

Resnick noted that 50-60% of Colles fracture cases are associated with an ulnar styloid fracture.^[19] An associated ulnar styloid fracture should prompt an investigation for tears of the TFC. The TFC extends from the rim of the sigmoid notch of the radius to the ulnar styloid and is thought to stabilize the distal radioulnar joint (see the image below).

PA and lateral views involve a minimal examination. The examiner should note the direction of displacement and angulation, the degree of comminution, the intra-articular involvement, and the radial length or variance in comparison with the normal side. The ulnar inclination is approximately 14° on the PA view, and the volar tilt (see the image below) is approximately 12° on the lateral view.

Two classification systems are used: the Association for Osteosynthesis (AO) system and the Frykman system (see the Tables 2 and 3, below).

Table 2. AO Classification of Colles Fractures (Open Table in a new window)

Table 3. Frykman Classification of Colles Fractures (Open Table in a new window)

The AO and Frykman classifications are useful in discussing prognosis.

Complications of the Colles fracture include compressive neuropathy, posttraumatic arthrosis, Volkmann ischemic contracture, acute carpal tunnel syndrome, and shoulder-hand syndrome.^[16]

Colles fractures occur more frequently in elderly persons, as a result of osteoporosis.^{[17, 20]}

Smith fracture

Robert Smith described the Smith fracture in 1847. An impact to the dorsum of the hand or a hyperflexion or hypersupination injury is thought to be the cause. A Smith fracture is usually called a reverse Colles fracture because the distal fragment is displaced volarly. It is often described as a garden-spade deformity. The ulnar head can be displaced dorsally (see the image below).

Anteroposterior (AP) and lateral views of the wrist involve a minimal examination. The criteria that are used to evaluate Colles fractures also apply to Smith fractures (see Table 4 and the image below).

Table 4. Thomas Classification of Smith Fractures (Open Table in a new window)

The complications of Smith fractures are similar to those of Colles fractures.

Barton fracture

John Rhea Barton characterized the Barton fracture in 1838.^[16] This fracture involves a dorsal rim injury of the distal portion of the radius. The volar Barton fracture is thought to occur with the same mechanism as the Smith fracture, with more force and loading on the wrist. The dorsal Barton fracture is caused by a fall on an extended and pronated wrist, increasing carpal compression force on the dorsal rim. The salient feature is a subluxation of the wrist in this die-punch injury.

The Barton fracture involves either the palmar or dorsal radial rim, and the mechanism is intra-articular. By definition, this fracture has some degree of carpal displacement, which distinguishes it from a Colles or Smith fracture. The palmar variety is more common than the dorsal type (see the images below).^[16]

PA and lateral views of the wrist involve a minimal examination, but a true lateral projection is needed to evaluate the degree of carpal subluxation. In 1992, Wood and Berquist suggested that trispiral tomograms or coronal and/or sagittal CT scans could be used to evaluate articular congruity of the distal radius.^[16]

Barton fractures are classified as dorsal or palmar (always intra-articular), and they always involve carpal subluxation.

Complications of Barton fractures are similar to those of Colles fractures.

Hutchinson, chauffeur's, or radial styloid fracture

The chauffeur's fracture derives its name from injuries that were acquired, in the days when motor vehicles were cranked, when a vehicle backfired. The force is described as a direct axial compression of the scaphoid into the radial facet. The radial styloid is fractured, with associated avulsion of the radial collateral ligament.^{[19, 16]} A chauffeur's fracture represents an avulsion related to the attachment sites of the radiocarpal ligaments or of the radial collateral ligament. Scapholunate dissociation and lesser arc injuries of the wrist may be indicated by a fracture line on the radial articular surface between the scaphoid and lunate fossae.

The PA view usually demonstrates the lesion. Wood and Berquist report that little or no abnormality is seen on lateral views.^[16]

Chauffeur's fractures are classified as simple or comminuted radial styloid fractures and as displaced or nondisplaced fractures. These injuries show no evidence of carpal subluxation.

Complications include scapholunate dislocation, osteoarthritis, and ligamentous damage.

Galeazzi, or Piedmont, fracture

A Galeazzi fracture results from a FOOSH mechanism with the forearm hyperpronated or from a direct impact to the dorsal radial wrist. The radial diaphysis at the distal and middle third junction is fractured, with associated subluxation of the distal radioulnar joint. On PA views, the radius is shortened and the radioulnar joint is disrupted.

Radioulnar distances greater than 2 mm are suggestive of a ligamentous injury and/or a tear of the TFC. On the lateral view, the distal radius is angulated either volarly or radially as a result of the pull of the brachioradialis muscle with more than 3 mm of ulnar displacement.^{[21, 16]} An associated ulnar styloid fracture also may be present.

PA views may show a displaced radial and ulnar styloid. The lateral view may reveal the associated radioulnar dislocation that is occult on the AP view.

Classification is based on the direction of displacement of the distal fracture fragment.

Complications include radial malunion, nonunion, and persistent subluxation of the radioulnar joint.^[16]

Essex-Lopresti fracture

The Essex-Lopresti fracture consists of a comminuted and displaced radial head fracture along with disruption of the distal radioulnar joint and interosseous membrane. The thickened ridge of the scaphoid and lunate facets dissipates the energy delivered to the wrist in a FOOSH injury and is thought to account for fractures that occur between the scaphoid and lunate facets of the radius. The fracture line originates at the junction of the scaphoid and lunate fossae on the radial articular surface and courses laterally in a transverse or oblique direction. The intra-articular distal radial fracture of the radial styloid is associated with an avulsion of the radial collateral ligament.

Routine PA and true lateral views are obtained. On the PA view, overlap, widening, or incongruity of the radioulnar joint should be noted. Resnick notes that careful radiographic positioning and measurements are essential, as is transaxial CT scanning or MRI, to assess the extent of displacement or subluxation of the radioulnar joint.^[19]

Complications are similar to those of a Colles fractures and include radioulnar joint instability and TFC damage.

Pediatric distal radial fracture

The distal one third of the forearm is the most common fracture site in children. Dicke notes that these make up 35.8-45% of all pediatric fractures. The primary mechanism of injury is a FOOSH mechanism. Unlike such falls in adults, these falls rarely lead to intra-articular fractures in children, but fractures can occur at the diaphyseal-metaphyseal junction or at the physis. Boys have a higher frequency of distal radial fractures than do girls.

Five classifications of pediatric fractures are used, as follows^[22] :

• Plastic deformation - This occurs most commonly in the ulna and fibula.
• Buckle (torus) fracture - In this, the diaphysis (cortical bone) causes the metaphysis to buckle under compressive forces.
• Greenstick fracture - This fracture occurs when the tension side of the bone fails as it is bent.
• Complete fracture - A complete fracture propagates through the entire bone and can occur as a spiral fracture, an oblique fracture, or a transverse fracture.
• Epiphyseal fracture - This fracture involves the growth plate and/or physis. The distal radial physis is the most frequently injured physis.

Fractures involving the physis are categorized as follows, using the Salter-Harris (SH) classification:

• Type I - A fracture through only the physis
• Type II - A fracture occurring through the physis and obliquely through the metaphysis
• Type III - A fracture occurring through a portion of the physis and longitudinally through the epiphysis
• Type IV - An oblique fracture extending through the metaphysis, physis, and epiphysis

A displaced pronator fat sign may be the only indication of a nondisplaced Salter-Harris type I fracture. Salter-Harris type II fractures are the most common, according to Waters,^[23] making up 58% of the fractures considered in a 1993 study by Dicke.

Complications of pediatric distal radius and ulnar fractures include nonunion or malunion, growth-plate arrest that leads to deformity, nerve and vessel damage, sympathetic dystrophy, overgrowth of the healing bone, and, in rare instances, compartment syndrome.

CT scanning is used to plan operative repair or to resolve uncertain findings on conventional radiographs. Optimal results are obtained when sagittal and coronal 2-mm sections are used. See the images below.

CT scanning may be useful in circumstances involving complex or occult fractures, an evaluation of the distal radioulnar joint and distal radial articular surface, an assessment of fracture healing, or a postsurgical evaluation.

CT scanning improves the accuracy of fracture alignment measurements.

MRI is not routinely used in the initial evaluation of acute distal radial fractures or of associated carpal injuries. However, the modality is useful in the assessment of bony, ligamentous, and soft-tissue abnormalities associated with distal radial fractures.

MRI is routinely used to evaluate the integrity of the intercarpal ligaments, the TFC, and the median nerve within the carpal tunnel. Compared with plain radiographs and scintigrams, MRI scans may be more sensitive in detecting early osteonecrosis associated with an evaluation of occult fractures and posttraumatic or avascular necrosis of the carpus.

Degree of confidence

The improved contrast resolution afforded by MRI improves the detection of marrow edema at the site of fracture, which is not radiographically detectable on CT scans.

Wood and Berquist quote a sensitivity of 100% and a specificity of 92% for MRI in the detection of TFC tears, compared with a sensitivity and specificity of 89% and 90%, respectively, for arthrography.^[16]

Ultrasonography may be used in pediatric patients to visualize the physes of children in whom mineralization of secondary growth plates has yet to occur. Ultrasonography may also be used in patients who lack bony landmarks. On ultrasonograms, cortical surfaces are echogenic or echoreflective, whereas cartilage or unossified physes are sonolucent or hypoechoic.^[24]

Bianchi et al found that ultrasonography is an effective, dynamic, and noninvasive technique with which to diagnose and evaluate damage to the extensor tendons and their synovial sheaths. The authors analyzed ultrasound examinations of 9 consecutive patients with a history of distal radial fractures treated by open reduction and internal fixation of the volar plate.^[25]

Nuclear scintigraphy can be used to detect fractures because the early osteoblastic reaction at fracture margins results in a focal linear accumulation of technetium-99m (^99m Tc) methylene diphosphonate (MDP) at the site. However, reports describe poor accumulation of the radiotracer in patients with congestive heart failure or chronic renal failure and in the elderly.^[24]

If a patient is symptomatic or if bony, cartilaginous, or ligamentous abnormalities are suspected despite normal radiographs, radionuclide bone imaging may be helpful. An occult fracture or other physiologically active osteochondral pathology must be excluded when an area of intense focal tracer accumulation is noted. Mildly increased focal tracer uptake suggests ligamentous or cartilaginous pathology. Lack of focal tracer accumulation on delayed images excludes osteochondral involvement.

Radionuclide bone imaging may be helpful in determining a fracture's age and for documenting fracture healing when radiographic results are inconclusive. It is also important in the diagnosis of RSD.

Degree of confidence

Bone scintiscan findings may remain positive for as long as 2 years as a result of vascular recruitment from trauma.^[24]

Metz and Gilula quote a sensitivity and specificity of 96% and 97%, respectively, in the diagnosis of RSD by using radionuclide bone imaging.^[26]

Angiography is indicated in cases involving a compromise of vascular structures, as reflected in the clinical presentation.