BREAK IN THE PELVIC RING Pelvic fractures include those that involve a break in the pelvic ring, fractures of a single bone without a break in the pelvic ring, and acetabulor fractures. Pelvic fractures involving a break in the pelvic ring can be complex and therefore difficult to classify. These injuries range from low-energy stable fractures to high-energy unstable patterns. The most clinically useful classification by Young ( Table. . . 2.65-.1.), is presented.7 It differentiates fracture patterns based on mechanism of injury and direction of causative force. Incidence of complications (i.e., urogenital and vascular) is correlated with the fracture pattern, making identification of the type more clinically significant and useful.
TABLE 265-1 Injury Classification Keys According to the Young System
Three main types of patterns have been identified. The first and most common mechanism, lateral compression (LC) (Fig 26.5.-5., Flg.ii2.65:6, Fig 265-7, F..i.g,.ni2.6.5-8
and Fig 2.6.5.-.9.)> accounts for close to half the injuries. Motor vehicle accidents in which a car is broadsided or a pedestrian struck from the side are examples.
Anteroposterior compression (APC) (Fig...265:10, Fig. .265zll, and Fig.iii265z12) is the second type, accounting for about 25 percent of injuries. Head-on motor vehicle accidents are the classic example. The least common mechanism is vertical shear (VS) (Fig 2.6.5z1.3.) typified by a fall or jump from a height, accounting for about 5
percent of fractures. A combination (CM) of other injury patterns make up the other 20 to 25 percent of injuries.
FIG. 265-5. Type I—lateral compression fracture: The lateral force is applied posteriorly ( arrow). This causes a crush effect on the SIJ: this may be visible radiographically as a sacral fracture (A). The characteristic fracture pattern of the pubic rami will be seen ( B). No ligamentous injury is seen.
FIG. 265-6. Type II—lateral compression fracture: The force is applied anteriorly ( arrow), causing the typical anterior public rami fractures ( B). In this case, however, rotation of the pelvis around the anterior sacral margin may occur, causing rupture of the posterior sacroiliac ligaments ( R). A crush fracture of the sacrum may also be seen (A).
FIG. 265-7. Alternatively (compared to Fig 2.65-6), a fracture of the iliac wing may occur which dissipates the rotational forces and thus leaves the posterior ligaments intact.
FIG. 265-8. Type III—lateral compression fracture: The force is applied anteriorly ( arrow), causing internal rotation of the anterior hemipelvis. Continuing through to the contralateral hemipelvis (arrow), the force causes it to rotate externally. The result is a pattern of lateral compression on the ipsilateral side, with apparent Ap compression on the contralateral side. This results in rupture of the posterior sacroiliac ligaments on the ipsilateral side ( R) and sacrospinous/sacrotuberous complex (7) and anterior ligaments (A) on the contralateral side. Typical public rami fractures ( B) are to be expected.
FIG. 265-9. Alternatively (compared to Fig 2.6.5.-8), as in type II B fractures (Hg.n26i5-7) there may be an iliac wing fracture sparing the posterior SIJ on the ipsilateral side.
FIG. 265-10. Type I—AP compression fracture: The force is delivered in an AP direction ( large arrow), tending to "open" the pelvis. This gives rise to mild splaying of the symphysis, due to rupture of the anterior sacroiliac ligaments.
FIG. 265-11. Type II—AP compression fracture: The AP force vector (large arrow) has caused further "opening" of the anterior pelvis, with additional rupture of the anterior sacroiliac, sacrotuberous, and sacrospinous ligaments.
FIG. 265-12. Type III—AP compression fracture: There is total disruption of the SIJ due to wide "opening" of the pelvis. All supporting ligament groups, including the posterior sacroiliac ligaments, may be disrupted.
FIG. 265-13. Vertical shear vector: The injury force vector is delivered in a vertical plane (large arrow), causing disruption along this line. Fractures of the pubic rami are usually seen anteriorly, while fractures of the sacrum, SIJ, or iliac wing are usually seen posteriorly. The fractures are vertical and are associated with vertical displacement of fragments. Ligamentous injury to the posterior (R) and anterior (A) sacroiliac ligaments may be seen, as well to sacrospinous/sacrotuberous ( T), and (possibly) symphysis ligaments.
The different injury types may be suggested by history, but can also be differentiated radiographically. The alignment of pubic rami fractures is one such clue to the mechanism and direction of force. Horizontal fractures suggest lateral compression injury, whereas vertical ones point to an anteroposterior direction of force. If there is sacroiliac joint diastasis and an associated crush fracture of the sacrum, then the injury is due to lateral compression. Central hip dislocations suggest a lateral compression mechanism whereas posterior dislocation suggests an anteroposterior force. With vertical shear patterns, fractures are vertical in alignment with vertical displacement of fragments. Based on the recognition of the fracture pattern, one can then predict the likelihood of severe hemorrhage or urogenital injury ( Table 265-2).
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