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Recognizing a fracture seems to hold a certain attraction for many. They are a favorite among those learning radiology, perhaps because of how common and seemingly straightforward they are. In this chapter we tell you how to recognize a fracture, describe it, name it, and avoid overlooking it.
A fracture is a disruption in the continuity of all or part of the cortex of a bone.
If the cortex is broken through and through, the fracture is called complete .
If only a part of the cortex is fractured, it is called incomplete . Incomplete fractures tend to occur in bones that are more elastic, such as those normally seen in children or abnormally in adults with bone-softening diseases, such as Paget disease (see Chapter 21 ).
Examples of incomplete fractures in children are the greenstick fracture, which involves only one part of, but not the entire, cortex and the torus fracture (buckle fracture), which represents compression of the cortex ( Fig. 23.1 ).
Radiologic features of acute fractures
Fracture lines , when viewed in the optimum orientation, tend to be blacker (more lucent) than other lines normally found in bones, such as nutrient canals ( Fig. 23.2A ).
There may be an abrupt discontinuity of the cortex , sometimes associated with abrupt angulation of the normally smooth contour of bone ( Fig. 23.2B ).
Fracture lines tend to be relatively straight but where they change their course, the changes are more acute in their angulation than any naturally occurring lines (such as growth plates ) ( Fig. 23.3 ).
The edges of a fracture may be jagged or irregular.
Sesamoids, accessory ossicles, and unhealed fractures ( Table 23.1 )
Sesamoids are bones that form normally in a tendon as it passes over a joint. The patella is the largest and most famous sesamoid bone ( Fig. 23.4A ).
Accessory ossicles are accessory epiphyseal or apophyseal ossification centers that fail to fuse with their parent bone ( Fig. 23.4B ).
Apophyses are growth centers that add to the shape of a bone on which a tendon or ligament inserts. Epiphyses add to the length of bones and form parts of a joint. Apophyses can be confused for fractures ( Fig. 23.4C ).
Old, unhealed fracture fragments can sometimes mimic acute fractures ( Fig. 23.4D ).
Unlike fractures, almost all of these small bones are corticated (i.e., there is a white line that completely surrounds the bony fragment) and their edges are usually smooth.
In the case of sesamoids, accessory ossicles, and unfused apophyses , they are usually bilaterally symmetric so that a view of the opposite extremity will usually demonstrate the same bone in the same location. Many also occur at anatomically predictable sites.
Sesamoids are almost always present in the thumb, posterolateral aspect of the knee ( fabella ) , and great toe (see Fig. 23.4A ).
Accessory ossicles are most common in the foot (see Fig. 23.4B ).
Feature | Acute Fracture | Sesamoids and Accessory Ossicles |
---|---|---|
Abrupt disruption of cortex | Yes | No |
Bilaterally symmetrical ∗ | Almost never | Almost always |
“ Fracture line” | Sharp, jagged | Smooth |
Bony fragment has a cortex completely around it | No | Yes |
∗ Old, unhealed fractures will not be bilaterally symmetric.
In a dislocation, the bones that originally formed the two components of a joint are no longer in apposition to each other. Dislocations can only occur at joints ( Fig. 23.5A ).
In a subluxation, the bones that originally formed the two components of a joint are in partial contact with each other. Subluxations also occur only at joints ( Fig. 23.5B ).
There is a common lexicon used in describing fractures to facilitate a reproducible description and to assure reliable and accurate communication.
Fractures are usually described using four major parameters ( Table 23.2 ):
The number of fragments
The direction of the fracture line
The spatial relationship of the fragments to each other
Whether the fracture communicates with the outside atmosphere
Parameter | Terms Used |
---|---|
Number of fracture fragments | Simple or comminuted |
Direction of fracture line | Transverse, oblique (diagonal), spiral |
Relationship of one fragment to another | Displacement, angulation, shortening, and rotation |
Open to the atmosphere (outside) | Closed or open (compound) |
If the fracture divides a single bone into two fragments , it is called a simple fracture.
If the fracture produces more than two fragments, it is called a comminuted fracture. Some comminuted fractures have special names.
A segmental fracture is a comminuted fracture in which a portion of the shaft exists as an isolated fragment ( Fig. 23.6A ).
A butterfly fragment is a comminuted fracture in which the central fragment has a triangular shape ( Fig. 23.6B ).
In a transverse fracture, the fracture line is perpendicular to the long axis of the bone. Transverse fractures are caused by a force directed perpendicular to the shaft ( Fig. 23.7A ).
Direction of Fracture Line | Mechanism |
---|---|
Transverse | Force applied perpendicular to long axis of bone; fracture occurs at point of impact |
Diagonal (also known as oblique) | Force applied along the long axis of bone; fracture occurs somewhere along shaft |
Spiral | Twisting or torque injury |
In a diagonal or oblique fracture, the fracture line is diagonal in orientation relative to the long axis of the bone. Diagonal or oblique fractures are caused by a force usually applied in the same direction as the long axis of the affected bone ( Fig. 23.7B ).
With a spiral fracture, a twisting force or torque produces a fracture like those that might be caused by planting the foot in a hole while running. Spiral fractures are usually unstable and often associated with soft-tissue injuries such as tears in ligaments or tendons ( Fig. 23.7C ).
By convention, abnormalities of the position of bone fragments secondary to fractures describe the altered relationship of the distal fracture fragment relative to the proximal fragment. These descriptions are based on the expected position the distal fragment would normally have occupied assuming the bone had not been fractured.
There are four major parameters most commonly used to describe the spatial relationship of fracture fragments. Some fractures display more than one of these abnormalities of position. The four parameters are:
Displacement
Angulation
Shortening/distraction
Rotation
Displacement describes the amount by which the distal fragment is off-set , front to back and side to side, from the proximal fragment. Displacement is most often described either in terms of percent (e.g., The distal fragment is displaced by 50% of the width of the shaft ) or by fractions (e.g., The distal fragment is displaced ½ the width of the shaft of the proximal fragment ) ( Fig. 23.8A ).
Angulation describes the angle between the distal and proximal fragments as a function of the degree to which the distal fragment is deviated from the position it would have assumed were it in its normal position. Angulation is described in degrees and by position (e.g., The distal fragment is angulated 15° anteriorly relative to the proximal fragment ) ( Fig. 23.8B ).
Shortening describes how much, if any, overlap there is of the ends of the fracture fragments, which translates into how much shorter the length of the fractured bone is than it would have been had it not been fractured ( Fig. 23.8C ).
The opposite term from shortening is distraction , which refers to the longitudinal distance the bone fragments are separated from each other ( Fig. 23.8D ).
Shortening (overlap) or distraction (lengthening) are usually described by a number of centimeters (e.g., There are 2 cm of shortening of the fracture fragments ).
Rotation is an unusual abnormality in fracture positioning almost always involving the long bones, such as the femur or humerus. Rotation describes the orientation of the joint at one end of the fractured bone relative to the orientation of the joint at the other end of the same bone.
Normally, for example, when the hip joint is pointing forward, the knee joint is also pointing forward. If there is rotation at the site of a fracture of the femoral shaft, the hip joint could be pointing forward while the knee joint is oriented in a different direction ( Fig. 23.9 ). To appreciate rotation radiographically, both the joint above and the joint below a fracture should be visualized, preferably on the same radiograph.
A closed fracture is the more common type of fracture in which there is no communication between the fracture fragments and the outside air/atmosphere.
In an open or compound fracture, there is communication between the fracture and the outside atmosphere (e.g., a fracture fragment penetrates the skin) ( Fig. 23.10 ). Compound fractures have implications regarding the way in which they are treated in order to avoid the complication of osteomyelitis. Whether a fracture is open or not is best diagnosed clinically.
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