W1 Role of Advanced Imaging in Distal Radius Fractures

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W1 Role of Advanced Imaging in Distal Radius Fractures

Dean Federman, MMBS, Eoin C. Kavanagh, FFR, RCSI, William B. Morrison, MD, George Koulouris, MMBS, MMed, FRANZCR

Distal radius fractures are the most common upper limb fractures and account for approximately one sixth of all fractures treated in emergency departments. These fractures are associated with significant patient morbidity^1,² and result in major economic impact, with loss of industrial manpower.³ Accurate assessment followed by appropriate management of these fractures is vital for optimizing function of the wrist and hand.

Conventional radiography is usually sufficient to diagnose simple and uncomplicated distal radius fractures. This modality is limited, however, by problems with patient discomfort, which cause degradation of image quality because of subsequent motion and loss of osseous detail owing to superimposition.⁴^–⁶ The reliability of radiography is diminished in the evaluation of complex fractures and is inherently inferior to advanced cross-sectional imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI).

A greater understanding of the importance of accurate presurgical fracture characterization and follow-up has led to an increasing reliance on CT and, to a lesser extent, MRI. In particular, the advent of multidetector CT (MDCT) has ensured that CT remains the gold standard in the imaging of distal radial fractures, particularly in clinical scenarios where plain radiographs yield insufficient information.

A single set of axial images acquired from an MDCT scanner has the capability of providing multiplanar reformatted images in the sagittal and coronal planes, offering superb cortical and trabecular bone resolution and accurate fracture characterization. MDCT also allows for rapid image acquisition times, minimizing motion artifact. The configuration of the fracture fragments involving the distal radial articular surface may be directly visualized, as may the degree of diastasis of the radioscaphoid and radiolunate fossae fragments, degree of articular incongruity, and possible ventral or dorsal cortical comminution. The sagittal and coronal planes are useful for showing the articular congruity and angulation, with step and gap deformity assessed in any of the three planes. The tendons may be assessed on soft tissue windows, allowing for their gross assessment. MDCT also allows for accurate postoperative fracture assessment because it effectively reduces beam hardening artifact resulting from metal to a minimum, a significant limitation of prior standard helical scanners.

MRI plays a specific role and is reserved for the assessment of concomitant soft tissue injuries, often suspected on presentation of ongoing postsurgical pain. MRI also may be used in circumstances where clinical suspicion for a fracture remains high, but radiographs and CT scans are negative. Technetium-99m MDP bone scintigraphy also may be used in similar circumstances, accurately identifying occult fractures and post-traumatic reflex sympathetic dystrophy.

Computed Tomography

CT is the modality of choice in characterizing the morphological characteristics of distal radius fractures. Unless the degree of fracture displacement on radiography is equivocal, simple displaced fractures traditionally do not require CT. CT is particularly useful, however, in the evaluation of complex comminuted distal radius fractures, serving as a preoperative road map in patients who have been selected for open reduction and internal fixation. CT also has an important role in the diagnosis of occult fractures, and is invaluable in postfracture healing assessment and in the evaluation of the postsurgical wrist, effectively excluding many potential complications.

Although several parameters have an impact on postfracture functional outcome, after correcting for severity of the initial fracture of the distal radius, the degree of intra-articular step and gap deformity correlates most strongly with prognosis, whereas this is not the case with dorsal and radial tilt.⁷ Fractures that heal with radiocarpal or distal radioulnar joint (DRUJ) step or gap deformities greater than 1 to 2 mm strongly correlate with premature arthrosis shown on radiographs.⁷^–¹⁰ Conversely, almost all patients achieve an excellent result with less than 1 mm of articular incongruity.⁸ This finding has been supported by animal models of articular fractures, where cartilage remodeling provides a congruent articular surface when displacement is less than 1 mm, whereas a step-off of greater than 1 mm typically does not.¹¹

CT scanning has been shown to be the most reliable method for identifying the extension of distal radial fractures to involve the articular surface, and accurately quantifies the degree of articular surface incongruity (Fig. W1-1).¹²^–¹⁵ CT reliably distinguishes between patients for whom surgery is indicated, preventing accelerated osteoarthritis in this group, from patients in whom only a conservative approach is required. Comparative studies between plain radiographs and CT scans not only reveal CT to be accurate at measuring the step and gap deformity, but also show that plain radiographs are 30% more likely to overestimate or underestimate displacement compared with CT.¹¹ CT is of particular benefit in evaluating the injured wrist in the presence of a plaster cast¹⁶ because osseous detail is not obscured to the same extent as it is with radiography. Accurate postreduction assessment for residual angulation and displacement is possible. The degree of comminution and size of fragments also are important considerations when assessing distal radial fractures, in planning management and predicting long-term outcome. CT accurately quantifies comminuted fragments and their size.^16,¹⁷

FIGURE W1-1 Method for assessing intra-articular gap and step deformity. The degree of intra-articular step deformity is represented by a line connecting points A and C on the longitudinal reformatted image (A) and line BC and the coronal image (B). The degree of gap deformity is defined as line BC (A) and line AC (B), respectively. CT allows for improved visualization of the fracture fragments compared with plain radiographs, as seen in the sagittal reformatted image (C).

Involvement of the DRUJ in distal radius fractures is similarly underestimated on radiographs compared with CT.^13,¹⁴ Sigmoid notch fracture step-off and articular gapping also are assessed with a greater degree of accuracy with CT.¹⁸ Subluxation or dislocation of the DRUJ with distal radius fractures may be overlooked. On a posteroanterior radiograph, the DRUJ space should measure approximately 2 mm; however, even a small degree of supination or pronation of the wrist from the neutral position renders analysis of the DRUJ on plain film inaccurate.^18,¹⁹ This limitation of patient positioning is overcome with CT scanning, which is the modality of choice in assessing the DRUJ. Apart from assessing fracture extension into the joint space, static and dynamic DRUJ instability can be assessed by obtaining CT images of the wrist in various positions of forearm rotation.²⁰

Postfracture assessment of the distal radius, including postsurgical change and complications, is improved with CT versus plain radiography owing to the avoidance of overlapping bone surfaces and plaster casts.¹⁷ This includes improved evaluation of bone bridging and graft incorporation.²⁰ The position of metal fixation devices, even when artifact is present, also is more accurately evaluated with CT, particularly with MDCT. Malunited distal radius fractures may be complicated by intra-articular incongruity and ulnar-positive variance, findings easily assessed with MDCT. Patients requiring additional treatment usually are managed with corrective wedge osteotomy and placement of an autogenous bone graft.²¹ MDCT with three-dimensional surface rendered images is increasingly used not only for appreciation of malunion, but also as a road map for surgery (Fig. W1-2). CT virtual preoperative planning, including virtual osteotomy of the distal radius, prediction of final positioning, and computer-assisted manufacturing of repositioning devices, has shown promising results for guiding surgical management.^22,²³

FIGURE W1-2 Anterior volume-rendered 3D reformatted image from a multidetector CT examination allows improved appreciation of the degree of fracture displacement of the distal radius, allowing the clinician to anticipate surgical findings.

Frequently, subtle radiographic lucencies of the distal radius may simulate fractures and are a cause for inconclusive, or even incorrect, reporting. Similarly, occult fractures of the wrist are sometimes suspected on the basis of physical examination or focal areas of increased scintigraphic uptake on bone scintigrams, despite normal plain films. CT has the capability of providing additional specificity to these findings, particularly with the use of three-dimensional reconstructions.^20,^24,²⁵

Limited interobserver reliability has been observed with most fracture classification systems,^12,^13,²⁶ including the classification systems of the distal radius. More recent literature has aimed at assessing the potential added value of three-dimensional CT reconstructions over conventional two-dimensional CT for distal radial fracture classification. Although these studies reveal improved intraobserver agreement on fracture classification, conflicting data surround the added benefit on interobserver reliability.^27,²⁸

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