In any case of trauma it is essential to take at least two views, preferably at right angles to one another. Sometimes a fracture or dislocation will be seen on only one view and so may be missed unless two views are taken. Similarly, the position of a fracture should never be assessed from a single view (Fig. 14.1).
The major advantages of multidetector computed tomography (MDCT) over plain films are:
- Better assessment of fractures in bones of complex shape, such as the spine and pelvis (Fig. 14.2) which can be aided by three-dimensional reformation of the CT images. Reconstructions to any desired plane (Fig. 14.3) or three-dimensional images (Fig. 14.4) are easily obtained on modern equipment. In the spine, fractures of the pedicles, laminae and articular facets as well as fragments displaced into the spinal canal are particularly well seen (see Fig. 14.3). In fractures of the pelvis, especially those around the hip joints, CT shows the relationship of the fractures to the joint as well as loose fragments within the joint (see Fig. 14.2). CT is invariably performed in acetabular fractures and fracture dislocations of the hip. It is also very helpful in tibial plateau fractures and fractures of the ankle, calcaneum and midfoot.
- Assessment of the extent of soft tissue damage, haematomas and of internal visceral injuries.
- In general, less manipulation of the patient is required, so that the examination of the severely injured individual is more comfortable and often safer. The examination is quick, an important factor in patients with serious internal injuries.
Magnetic Resonance Imaging
Even though cortical bone does not produce a magnetic resonance signal, a fracture can be seen as a dark line across the bright signal of the fat in the marrow on a T1-weighted magnetic resonance imaging (MRI) scan (Fig. 14.5a). Increased signal intensity is seen within the bone, representing haemorrhage and/or oedema on a T2-weighted scan; a STIR sequence has a T2-weighted appearance with saturation of the fat signal intensity (Fig. 14.5b). Sometimes a bone bruise may be visible on MRI (Fig. 14.6) even though there is no discernible fracture on a conventional radiograph.
Magnetic resonance imaging is also very useful for demonstrating injury to soft tissues such as muscle, tendons and ligaments and is particularly useful in knee injuries (Fig. 14.7). MRI is the best examination for sports injury and repetitive strain injuries.
It is also the best method for demonstrating scaphoid fractures and its use has been advocated as the initial investigation.
Radionuclide Bone Scanning
Fractures may not be visible on plain films, and, in these instances, radionuclide bone scanning maybe helpful (Fig. 14.8), although increasingly MRI is often used in these circumstances. The bone scans show increased activity at injured sites within 2–3 days. Increased activity persists for as long as the fractures are healing, often lasting several months. Multiple fractures occasionally give a picture resembling metastases, but usually the distribution suggests injury.
Frequently, a fracture is very obvious but in some cases the changes are more subtle. Fractures may be recognized or suspected by several signs (Box 14.2). A fracture line may been seen as a lucent line. This may be very thin and easily overlooked (Fig. 14.9). Occasionally, the fracture appears as a dense line from the overlap of the fragments (Fig. 14.10). A step in the cortex may be the only evidence of a fracture (Fig. 14.11). Interruption of bony trabeculae is of use in impacted fractures where there is no visible lucent line. This is, however, a difficult sign to evaluate (Fig. 14.11). Bulging or buckling of the cortex is a particularly important sign in children, where fractures are frequently of the greenstick type (Fig. 14.12). Soft tissue swelling may be a valuable guide to the presence of an underlying fracture. A joint effusion may become visible following trauma, and, as in elbow fractures, displaced fat pads may indicate an occult radial head fracture (Fig. 14.13).
- Fracture line (lucent or dense)
- Step in the cortex
- Interruption of bony trabeculae
- Bulging or buckling of the cortex
- Soft tissue swelling
- Joint effusion
Some injuries are likely to produce fractures in more than one site. With tibial fractures, for example, the fibula is frequently also broken but the fractures may be a considerable distance apart. Certain bones (e.g. the pelvis and mandible) often fracture in two sites, only one producing severe symptoms. In these situations, all likely fracture sites should be included on the films.
The joint surfaces no longer maintain their normal relationship to each other. Careful evaluation for an associated fracture should be performed.
Further Plain Film Views
Injuries may sometimes be invisible even with two views taken at right angles to each other. If the radiographic findings are equivocal, or if there is clinical suspicion of bony injury with normal radiographs, then further films should be taken as follows:
- Different projections, e.g. oblique views (Fig. 14.14).
- Stress films. A film taken with a joint under stress may show that it is unstable due to ligamentous damage. Stress films are helpful in ankle injuries when forced inversion and eversion may show movement of the talus (Fig. 14.15).
- Flexion and extension views. In the cervical spine, injury may cause alteration in the alignment of the posterior borders of the vertebral bodies. This is usually much more obvious on a film taken with the neck flexed (Fig. 14.16
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