2 Radiology of the Fractured Radius

10.1055/b-0039-169242

2 Radiology of the Fractured Radius

Mark Ross, Patrick Groarke

Abstract

This chapter provides guidelines for the radiographic assessment of distal radius fractures. We discuss plain radiographic parameters and their relationship in predicting stability and outcome and determining the adequacy of reduction and fixation strategy where indicated. We will review how to interpret computed tomography in the different planes and the relevance of fragmentation patterns. The value of magnetic resonance imaging and other modalities in assessing the fractured distal radius will be reviewed.

2.1 Introduction

Radiographic assessment of the distal radius should be undertaken when the mechanism of injury and presence of deformity or bony tenderness leads to clinical suspicion of a fractured distal radius. Understanding the imaging that needs to be obtained is a key element in the surgeon’s ability to decide on appropriate management. The interpretation of the imaging is an even more important element in planning management, and if fixation is indicated, what fixation method should be employed. It is also critical to understand that each option in the imaging process provides very specific information, which may not be available in other images. In this way, prereduction radiographs (XRs) inform certain aspects, postreduction XRs provide different information, and each plane of computed tomography (CT) imaging is best suited for specific anatomic components of the injury pattern.

The functional demands of each patient differ. As a consequence, the age (physiologic as well as chronologic), employment, and lifestyle of each patient must be used to place the radiographic parameters into context. The goal of treatment is to provide a painless extremity with good function. In surgical decision-making, special attention should be given to the patient’s bone quality. In addition, elderly patients with low demands may tolerate greater variance in many of the radiographic parameters that will be discussed in this chapter. However, with increasing activity level and functional expectations in an aging population, it is increasingly difficult to predict what may be tolerated by elderly patients. ¹

One of the most challenging considerations is whether the fracture pattern (pre- or postreduction) is stable. That is, is this the position that the fracture will ultimately heal in? The injury (prereduction) XR is very important in determining stability as it provides more information about maximum displacement and the energy of the injury. It is vital that the surgeon considers this series of images when making clinical decisions. Wherever possible, every effort should be made to obtain and assess the injury film. Consideration should also be given to this issue when the fracture has undergone some form of traction or closed reduction prior to initial radiographic assessment as the degree of displacement may be underestimated. A careful history of the interventions following injury is, therefore, vital. Following reduction and institution of closed treatment, it may be possible, with careful attention to cast changes, to control dorsal tilt; however, it is frequent to see the recurrence of radial shortening back to the injury position; thus, this must be considered when deciding on management.

Both increasing age of patients and increasing obesity in younger patients ² have led to an increase in fractures that are comminuted. Comminuted fractures can be difficult to assess on plain XRs, but by applying the same system to evaluate them and with the proper interpretation of the CT, the surgeon can plan the fixation technique where indicated.

2.2 Plain Radiographs

Standard XRs are indicated in all suspected distal radius fractures (DRFs). We recommend XR before and after reduction. As noted above, the assessment of stability is best conducted using the injury (prereduction) XRs. Standard views include posteroanterior (PA) and lateral XR. Oblique views can also be helpful in bringing the volar portion of the radial and ulnar aspect of the radius as well as the dorsal ulnar corner (DUC) into view. These provide a two-dimensional image of a three-dimensional (3D) structure but understanding the normal parameters on each view can allow clarification of articular fragments even where CT images are not available. It is important to be able to determine what constitutes a true PA and lateral because many images can be rotated due to patient’s inability to position the arm correctly due to pain, and many parameters are validated in relation to the orthogonal XRs.

2.2.1 Injury (Prereduction) Radiographs

The value of these films should not be understated to those carrying out emergent management such as closed manipulation so as to discourage reduction before imaging. This can happen where a grossly deformed wrist presents. Clearly, if the skin is threatened or there are significant neurological symptoms and XRs cannot be obtained emergently, the restoration of gross alignment takes priority; however, careful documentation of the deformity should be made. Injury films can reveal small, nondisplaced, and intra-articular fragments. These fragments might not be visible after anatomical reductions and cast application, which might mask the severity of the fracture. The original displacement and angulation of the fracture can be an indicator of instability. In a study of 406 DRFs, initial displacement was associated with worse QuickDASH score, worse EQ-5D score, reduced grip strength, and reduced range of motion (ROM). ³

2.2.2 Postreduction Radiographs

Although potentially obscured by cast material, these images guide where fragments lie in relation to each other and what type of fixation should be considered. In addition, they guide the adequacy of reduction although should not be used for determining the stability of the fracture and propensity for loss of position (▶Fig. 2.1).

**Fig. 2.1** **(a)** Prereduction film demonstrates significant displacement and implies an unstable fracture. **(b)** Postreduction image demonstrates articular surface involvement more clearly.

2.2.3 Parameters Can Change with Time

Where nonoperative management is undertaken, follow-up XRs at 1- and 2-week intervals would be considered a minimum and we have observed ongoing loss of position out to 6 weeks and beyond in cast treatment.

CT is more accurate in measuring the change in dorsal angulation over time in DRFs when compared to XRs. ⁴ However, the cost and high dose of radiation are prohibitive in most healthcare systems, and benefits from this increased accuracy have not been clarified.

2.2.4 Radiograph of the Opposite Side

In severely comminuted fractures, or where the fragments have been inadequately reduced, it might be difficult to establish what the patient’s normal parameters should be. An XR of the uninjured opposite side can be helpful for comparison. Coronal plane translation, as will be discussed later, can be guided by the uninjured side. Contralateral XRs can also give an indication to the energy load to failure of the distal radius by defining normal ulna variance for that patient, given the significant variance in radial length. Increased ulnar variance (loss of radial length) after fracture is also associated with reduced bone mineral density in the distal radius. ⁵

Parameters may vary between populations but the difference is likely to lie within the ranges described below. ⁶

2.2.5 Posteroanterior View

The ulnar border of the ulnar styloid should be continuous with the ulnar border of the shaft. Pronation or supination can result in the ulnar styloid being partially overshadowed by the distal ulna shaft. The radial border of the ulna shaft is concave on a true PA view. Moreover, if the shafts of the radius and ulna are seen to converge, this indicates pronation. A full pronation view has the effect of shortening the radius by at least 0.5 mm.

The PA view presents the carpal facet horizon. This is a radiodense line that represents the volar rim of the lunate facet and medial half of the scaphoid facet, in a radius with normal volar tilt. It extends ulnarward to the sigmoid notch. In a wrist with preserved volar tilt, the XR beam is tangential to the volar half of the articular surface (▶Fig. 2.2). The DUC and dorsal rim are distal to this horizon and less well visualized (▶Fig. 2.3). In a dorsally angulated fracture, the radiodense line will represent the dorsal rim and DUC as the XR beam will be tangential to it (▶Fig. 2.4). The main value of the carpal facet horizon is that a step-off in it will indicate an articular step-off, and understanding whether one is viewing the dorsal or volar half of the joint will help to locate that articular involvement. ⁷

**Fig. 2.2** The radiograph (XR) beam is tangential to the volar half of the joint in an intact or undisplaced radius.

**Fig. 2.3** The denser line represents the volar rim when the radius is intact or not dorsally tilted.

**Fig. 2.4** In the dorsally tilted radius, the denser line becomes the dorsal rim as it rotates into a tangential relationship to the radiograph (XR) beam.

The other implication of the separate representation of the volar and dorsal aspects of the ulnar corner is where to measure ulnar variance and radial inclination from. It has been suggested that true radial length is represented by the average point between the dorsal and volar ulnar corner on the PA view. This may be termed the central reference point (CRP). ⁷ Many studies published up until this point have failed to clarify their method for determining the measuring point for ulnar variance. Perhaps radial length may be a more reproducible measure of true shortening of the radius than ulnar variance because of this factor.

2.2.6 Lateral View

It should be taken in neutral rotation. On a true lateral XR, the pisiform is located directly over the distal pole of the scaphoid. If the pisiform lies dorsal to the distal pole of the scaphoid, the forearm is rotated into pronation.

Another method of ensuring the wrist is in neutral rotation and is to use the scaphopisocapitate relationship. ⁸ This is described where the rotation of the wrist is set at a position in which the volar margin of the pisiform bone lies at the central third of the interval between the volar cortex of the scaphoid tubercle and volar capitate. Wrist position is also important although may be compromised by pain or deformity in the acute setting. Larsen et al defined the true lateral XR as when the long axis of the radius and third metacarpal bone are collinear in neutral rotation. ⁹

Carpal alignment is determined on the lateral. A line extending from the volar surface of the radial shaft (not the metaphysis) should bisect the center of rotation of the proximal pole of the capitate ⁷ (▶Fig. 2.5).

**Fig. 2.5** Carpal alignment with the distal radius is assessed using a line up the volar surface of the radial shaft, which should intersect the center of the head of the capitate. ⁷

2.3 Plain Radiographic Parameters

Radiographic parameters are assessed in terms of extra-articular alignment and intra-articular fragmentation/congruence to determine stability and acceptability of reduction.

In general terms, comminution is a key extra-articular factor in assessing fracture stability (▶Fig. 2.6). It is an indirect measure of the energy of the injury and implies a more unstable fracture pattern. Volar comminution, in particular, is associated with a significantly higher chance of secondary displacement. Malalignment of the volar cortex on the lateral projection after closed reduction is a significant risk factor for loss of position. Comminution remains a subjective assessment, which is difficult to quantify.

**Fig. 2.6** Significant dorsal comminution implies a higher energy injury that would have had more displacement at the time of injury and may be less stable.

The following parameters are listed as the average measure with normal ranges as defined by Geissler et al ¹⁰ The wide variability in these parameters necessitates consideration of obtaining XRs of the opposite side where any concerns regarding the adequacy of reduction exist.

It should be noted that there have been some concerns raised regarding the interobserver error for these parameters when assessed visually as opposed to digitally, which has raised caution in relation to formulating treatment plans based on purely visual assessments. ¹¹

2.3.1 Posteroanterior View

Radial inclination—the angle between the ulnar aspect of the articular surface of the radius and the radial styloid is 23° (range: 13–30°).
- The reference point on the ulnar side of the radius should be halfway between the dorsal and volar rims (CRP; ▶Fig. 2.7).
Assessment of the degree of shortening of the radius relative to the ulna—there are a number of methods for quantifying shortening of the radius:
- Radial height (also called radial length)—the difference in length between the distal surface of the ulnar head and the tip of the radial styloid: 12 mm (range: 8–18 mm) (▶Fig. 2.8).
- Ulnar variance—refers to the relative lengths of the distal articular surfaces of the ulnar part of the radius and the ulna. Where the ulnar is shorter, the value is negative: negative 1 mm (range: positive 2 mm to negative 4 mm). As noted by Medoff, it is important to utilize CRP when calculating this parameter (▶Fig. 2.9).
Coronal plane translation—is measured by drawing a line along the ulnar aspect of the radial shaft proximal to the metaphyseal flare and extended distally through the proximal row of the carpus on the PA XR. This line intersects the lunate. The point of intersection is evaluated by drawing a second line along the widest part of the transverse width of the lunate on the anteroposterior (AP) XR, parallel to the distal radial articulation. The point of intersection of these two lines is measured from the radial side of the lunate to determine the percentage of lunate radial to this point (▶Fig. 2.10). Ross et al looked at 100 PA XRs of normal wrists. The mean was 45.48% of the lunate, radial to the bisecting line. This showed high levels of inter- and intraobserver agreement between three fellowship-trained upper limb surgeons. ¹²

**Fig. 2.7** Radial inclination angle is calculated by the angle between the ulnar aspect of the radius and the radial styloid. **(a)** Dorsal rim of radius. **(b)** Volar rim of radius. **(c)** Average of a and b. **(d)** Radial styloid. **(e)** Radial inclination angle.

**Fig. 2.8** Radial height (length). **(a)** Distal ulnar surface. **(b)** Radial styloid. **(c)** Radial height.

**Fig. 2.9** Ulnar variance. **(a)** Dorsal rim of radius. **(b)** Volar rim of radius. **(c)** Average of a and b. **(d)** Distal ulnar surface. **(e)** Ulnar variance.

**Fig. 2.10** Coronal translation is calculated by determining how much of the lunate lies radial to a line drawn along the ulnar shaft of the radius before the metaphyseal flare. Normally, less than half of the lunate lies radial to this line.

It has been suggested that radial translation of the distal fragments is a marker for distal radioulnar joint (DRUJ) instability. ¹³ Residual radial translation contributes to DRUJ instability because malpositioning of the distal fragment results in loss of tension of the distal portion of the interosseous membrane (IOM) and pronator quadratus (PQ). A consequence of this tension loss is that even if the sigmoid notch is well positioned in all other respects (length, coronal tilt, and sagittal tilt), the ulnar head may not be held firmly into the concavity of the sigmoid notch, possibly contributing to the instability of the DRUJ (▶Fig. 2.11).

**Fig. 2.11** This patient has residual radial translation. The fixation of the ulnar styloid may have been unnecessary if the translation had been corrected, thereby tensioning the distal interosseous membrane (IOM).

Wolfe et al contributed to this observation by confirming in a cadaver study that residual translation of the distal radius fragment in DRFs can indeed contribute to DRUJ instability by detensioning the IOM. ¹⁴

Volar locking plate fixation typically addresses the parameters of volar tilt, radial height, and radial inclination. However, it does not routinely force the surgeon to look for and correct radial translation because it is essentially a flat plate on a flat surface. If the radial translation is not looked for and addressed intraoperatively, DRUJ instability may exist postoperatively. Although preoperative radial translation deformity may be more likely to occur when there is greater disruption of the ulnar-sided stabilizing structures, this makes it even more important for the surgeon to be aware of this deformity and to ensure that from a technical perspective, the radial deformity is corrected at the time of surgery. ¹⁵

Other measurements in the literature include radiolunate relations, but these are less commonly used. ¹⁶

2.3.2 Lateral View

Volar tilt—At the articular surface of the radius, a tangent line is drawn from dorsal to volar, followed by a line perpendicular to the long axis of the radius. The angle between these lines is the volar tilt of 12° (range: 1–21°) (▶Fig. 2.12).
Teardrop angle ⁷ —The teardrop is best seen on the inclined lateral view. It represents the U-shaped outline of the volar rim of the lunate facet. A line drawn down the central axis of the teardrop (parallel to the subchondral bone of the volar rim) subtends an angle of 70° to a line extended from the central axis of the radial shaft (▶Fig. 2.12, ▶Fig. 2.13). Loss of the relationship between the lunate and the teardrop can also reveal carpal subluxation. Where there are separate dorsal and volar articular fragments, a diminished teardrop angle may imply dorsal rotation of the volar fragments independent of dorsal fragments, which may exist in spite of apparent maintenance of volar tilt. The teardrop angle can also give a clue to the causative mechanism of volar rim fragments and therefore inform reduction strategies. A volar shear injury will often have a maintained teardrop angle with no rotation of the volar rim fragment (▶Fig. 2.14). In this case, simple buttressing of the fragment will adequately reduce and stabilize it. Conversely, a diminished teardrop angle implies dorsal rotation of the volar rim fragment. This is usual in a dorsally directed axial load injury with traction on the volar rim fragment from the volar wrist ligaments (▶Fig. 2.15). In this circumstance, a simple buttress-type fixation will not derotate the fragment and an alternate fixation strategy may be required.
AP distance ⁷ —This is the distance described by Medoff between the apices of the dorsal and the volar rims of the lunate facet of the radius ⁷ (▶Fig. 2.16). This is sometimes better appreciated on a 10 to 15° tilt lateral (with the forearm elevated up towards the XR beam). The optimum angle is determined by the radial inclination of the distal radial articular surface. If the AP distance of the radius is significantly greater than the AP dimension of the lunate, it implies an intraarticular fracture with separation between the dorsal and volar rim (▶Fig. 2.17, ▶Fig. 2.18). When there is a fracture in the coronal plane with significant separation, this may be the only plain radiographic parameter that is abnormal. Importantly, this articular incongruity may involve the sigmoid notch.