Chance Fracture |
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Chance fracture is an unstable spinal injury first described in 1948 as
a distinctive flexion-distraction pattern that splits the vertebra
horizontally. What makes this fracture conceptually important is that
it involves all three columns of the spine as defined by the
three-column model. The anterior column comprises the anterior
longitudinal ligament, the anterior annulus, and the anterior
two-thirds of the vertebral body; the middle column includes the
posterior third of the vertebral body, the posterior annulus, and the
posterior longitudinal ligament; and the posterior column encompasses
the posterior bony elements and the posterior ligamentous complex.
Because an injury involving at least two of these three columns is
considered mechanically unstable, and because a Chance fracture
typically produces a distraction injury of the middle and posterior
columns with or without an anterior compression component, it is by
definition an unstable lesion. The horizontal fracture line propagates
from posterior to anterior, coursing through the spinous process,
lamina, pedicles, and into the vertebral body, without lateral
displacement or rotation of the fragments. The mechanism is a sudden deceleration of the trunk against a fixed point, most classically the lap portion of a seat belt during a motor vehicle collision. When the vehicle decelerates abruptly, the restrained pelvis remains anchored while the upper body is thrown violently forward, forcing the spine to hyperflex over the belt, which acts as a fulcrum. This generates tension across the posterior elements and, in more severe cases, compression of the anterior vertebral body. The association with lap belts, recognized in the 1960s, gave the injury its alternate name of "seat belt fracture." Although motor vehicle collisions dominate, the same flexion-distraction forces can arise from falls from height, assaults, extreme sports such as rodeo and snowboarding, and military blast events involving armored vehicles. A less familiar variant occurs iatrogenically at the ends of long spinal fusion constructs, where the pedicles split along their longitudinal axis into cranial and caudal fragments, producing proximal or distal junctional failure without any antecedent trauma. Epidemiologically, thoracolumbar spine fractures are common, and roughly 2% of blunt trauma patients sustain one. The thoracolumbar junction is the second most frequent site of spinal injury after the cervical spine. Chance fractures classically cluster at the T10–L2 transition in adults, whereas in children they tend to occur in the mid-lumbar region. There is a male predominance and a tendency to affect children and young adults, with reported mean ages in the mid-twenties. The location difference between age groups has direct clinical consequences: children are more likely to fracture L1–L3, while adults more often fracture the thoracic spine, including levels such as T4–T6 and T10–T12 that are rarely involved in children. The most clinically dangerous feature of Chance fractures is their strong association with intra-abdominal injury. The same belt that fractures the spine crushes the viscera between the restraint and the vertebral column, and the reported incidence of concomitant abdominal injury ranges widely from roughly a third to nearly nine out of ten cases, commonly cited as high as 50%. The most feared associated injuries are hollow viscus perforations and mesenteric lacerations, both of which carry substantial mortality. This risk is markedly higher in children. When a Chance fracture is present, pediatric patients have a concomitant intra-abdominal organ injury far more often than adults—about 63% versus 23%—and hollow viscus injury in particular is dramatically more frequent, roughly 51% versus 8%. Interestingly, rates of solid organ injury are nearly identical between children and adults, so the excess risk in children is driven specifically by bowel and mesenteric injury. This pattern holds even when the analysis is restricted to collisions alone, which argues that the difference reflects anatomy rather than mechanism. The likely explanation lies in belt positioning and body proportions: children's belts frequently ride too high across the abdomen rather than the pelvis, creating a fixation point over soft viscera, and the pediatric abdomen is more compliant with underdeveloped iliac crests. The higher rate of lumbar fractures in children mirrors this higher-riding belt. The practical result is a much greater need for surgical abdominal intervention in children. Clinically, the injury is treacherous because patients typically present with back pain but no neurological deficit, so the fracture can be overlooked. Neurological signs appear only when there is cord or cauda equina compromise. A critical physical finding is the "seatbelt sign"—linear bruising or abrasion across the abdomen in the belt's distribution—which should sharply raise suspicion for both the fracture and underlying visceral injury, and which can also appear on CT as fat stranding in the anterior abdominal wall. The great danger is delayed presentation of bowel injury. Several documented cases illustrate a patient arriving hemodynamically stable with only subtle initial imaging findings, then deteriorating hours later as a bowel perforation or complete transection declares itself. Peritoneal signs develop slowly with small bowel injury because luminal contents are relatively neutral and bacterial load is low; a rising heart rate as part of the systemic inflammatory response may be the first physical clue. For this reason, close serial monitoring of vital signs, laboratory values, and abdominal examination is essential, with repeat CT recommended when the picture is equivocal or the patient worsens, and exploratory laparoscopy or laparotomy when perforation is suspected. In the context of fever, abdominal pain, and tachycardia in a child with a Chance fracture, the appropriate action is to proceed to the operating room out of concern for hollow viscus injury. For diagnosis, CT is the imaging modality of choice in patients sixteen and older, superior to radiography for detecting the fracture and for evaluating associated abdominal injury; coronal and sagittal reformations are essential given the horizontal orientation. In younger children, radiography is often the recommended first study, though CT obtained for abdominal evaluation typically suffices. MRI outperforms CT for soft tissue and ligamentous injury and should be obtained when ligamentous disruption or cord compromise is suspected, because purely ligamentous Chance injuries are much harder to detect and more likely to be missed. A sternal fracture is an additional sign of instability. Management depends on fracture displacement and the nature of the injury. A purely osseous, non-displaced fracture without neurological deficit can be treated conservatively with a rigid brace or hyperextension cast, typically for eight to twelve weeks, with high union rates. Displaced fractures with a significant bony gap, neurological deficit, or ligamentous involvement require surgery, because soft tissue injuries will not heal with bracing and instability will persist. The mainstay of surgical treatment is posterior pedicle screw fixation to reconstruct the posterior tension band, achieving realignment, reduction, and stabilization; this may be performed open or percutaneously, with fusion reserved as the final goal when ligamentous injury is present. Reduction of kyphosis is important to prevent painful post-traumatic sagittal malalignment. Prognosis correlates with the degree of kyphosis, and outcomes after surgical stabilization are good in the great majority of patients, though residual low back pain remains a common long-term complaint. Ultimately, optimal care depends on an interprofessional team maintaining a high index of suspicion so that neither the fracture nor its dangerous abdominal companions are overlooked. References: 1- Bourghli A, Obeid I, Boissiere L, Vital JM, Tabboush Z, Al Sarawan M. Management of a high thoracic chance fracture. Eur Spine J. 27(7):1547–1552, 2018 2- Hazen BJ, Keane OA, Vandewalle RJ, Grady Z, Wetzel M, Chern JJ, Santore MT. Difference in Presentation and Concomitant Intra-Abdominal Injury with Chance Fracture in Pediatric and Adult Populations. Am Surg. 89(6):2486–2491, 2023 3- Comadoll SM, Holton KJ, Polly DW Jr, Schmitz MW, Haselhuhn JJ, Soriano PBO, Martin CT, Jones KE, Sembrano JN. Chance Fracture Pattern Presenting in Proximal Junctional Failure. J Am Acad Orthop Surg Glob Res Rev. 7(8):e23.00039, 2023 4- Koay J, Davis DD, Hogg JP. Chance Fractures. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Aug 14. 5- Destinval C, Larmure O, Journeau P, Lemelle JL. Seat belt syndrome with caecal perforation and Chance fracture in an adolescent. BMJ Case Rep. 16(10):e254631, 2023 6- Huang CK, Lee CC, Kwok CM. Chance fracture at L2 followed by delayed jejunal transection due to a motor vehicle collision: A case report and review. Trauma Case Rep. 48:100968, 2023 |
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