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Case Report |
1 All authors: Radiological Sciences, Oklahoma University Health Sciences Center, 1200 Everett Dr., Rm. ET 1606, Oklahoma City, OK 73104.
Received November 19, 2003;
accepted after revision February 2, 2004.
Address correspondence to J. M. Davis
(Joel-Davis{at}ouhsc.edu).
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She was seen initially at an outside facility, with a reported Glasgow Coma Scale score of 3 and no visual, verbal, or motor responses. She presented with a transverse abdominal ecchymosis (seat-belt sign) but was not injured intraabdominally. In addition, she presented with bruising on her upper chest, particularly around the shoulders. On arrival at the trauma center, she underwent radiography and CT of the cervical and thoracic spine that showed bilateral pulmonary contusions; a paraspinal hematoma; right first and second rib fractures; and complex fractures of the upper thoracic spine—specifically, fractures through the transverse processes of T1, T2, T4, and T5 on the left as well as bi-lateral transverse process fractures of T3, fractures of the pedicle and lamina and posterior facets of T3, and compression fractures of the T4 and T5 vertebral bodies (Figs. 1A, 1B, 1C). Four hours after admission, her state of consciousness improved to a Glasgow Coma Scale score of 11, but she was insensate below the level of the nipples and was unable to move her legs. MRI later revealed a cord edema from C7 to T4 with spinal canal narrowing at T3 due to a retropulsed fragment (Figs. 1D and 1E). Posttraumatic bone marrow edema was also present from T3 to T7.
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Definitions of the Chance fracture vary in the literature, but most are based on the three-column model of the spine proposed by Denis [4]. The agreed mechanism of injury is one of flexion–distraction. Different theories exist, however, as to whether all three columns fail in tension or whether the anterior fails in compression and the middle and posterior fail in tension. Difference of opinion also exists as to how ligamentous injury fits this fracture pattern. On the basis of our review of the literature, we have concluded that fractures of the spine are divided into categories based on mechanism of injury, with a Chance fracture being a flexion–distraction type of all three columns, with all failing in tension. We also concluded that simultaneous ligamentous injury is variable with Chance fracture. Ligamentous injury is important to describe because of its instability and because surgical intervention may be necessary to correct this instability.
The mechanism of action has been thoroughly described as a flexion distraction around a fulcrum, most commonly the seat belt [2, 3]. The point of motion in the body impacting against this fulcrum is normally the spine itself. In the Chance fracture mechanism, the fulcrum (lap belt) is anterior to the spine and high-energy motion results in tension failure of the spine. Because the tensile strength of ligaments is greater than that of bone, the bone elements fail before the ligaments. However, the forces are often significant enough for the ligaments to also fail, producing an unstable injury pattern. Thus, an obvious connection can be made between the mechanism of action and the anatomic location of injuries.
Relating differences in anatomy to mechanisms of injury, Smith and Kaufer [5] reported in 1969 that the typical Chance fracture occurred between L1 and L3. Most injuries of the lower back are at the thoracolumbar junction because of its relative increased mobility. This also holds true for the cervicothoracic junction. The most common level of cervical injury varies according to patient age and changes in anatomy with aging. Argan et al. [6] described the variation in the pediatric anatomy and suggested it as a reason for the increased incidence of this type of fracture in children and its greater association with internal injury. They concluded that the head–body weight ratio is higher in children because of children's higher center of gravity and subsequent greater lever arm, which produces greater tensile forces surrounding the axis of rotation. They also concluded that children with seat belt fractures have more severe internal injuries because of underdevelopment of the rib cage and pelvis. Thus, ample evidence exists to conclude that anatomy plays a part in the mechanism of injury and the injury pattern.
The lack of reports on Chance fracture in the upper thoracic spine is, in part, due to anatomy. The rib cage provides obvious support to the thoracic spine, and not as much motion is present in these segments as in the lumbar spine. Because of physics, a seat belt most commonly acts as the fulcrum and therefore the area of injury is lower than the thoracic spine. In our patient, no anatomic variations were known, but because of the nature of her injury and the obvious bending of the steering wheel, we deduced that the steering wheel acted as the fulcrum at the level of the upper thoracic spine. The bending of the steering wheel also confirmed the presence of adequate force to overcome the surrounding bone support. Whether our patient was wearing a shoulder-belt component is not clear. Either she was not and hit the wheel, or she was and the seat belt failed. Such a failure is not as unlikely as it may seem, as noted recently by Meyer et al. [7] in a study of seat belt restraint systems during rollover. They noted that most seat belt mechanisms failed during multidirectional vehicle acceleration pulses in multiple planes and multiple impact (rollover) accidents. The emergency locking seat belt retractors have been designed to be effective in horizontal crashes, but their response in multiplanar accelerations is unpredictable. Results showed that pendulum sensors and ball-and-cage type sensor systems are appropriately sensitive to horizontal accelerations but fail to respond to purely vertical accelerations. In our patient, vertical forces were a significant component of the accident. This evidence leads us to believe that either she had extricated herself from the shoulder component or the seat belt failed because of the rollover nature of the accident.
Injuries associated with Chance fractures often result in greater morbidity and mortality rates than the fracture itself [8]. Unfortunately, these associated injuries are sometimes over-looked [9]. Evidence exists to support the approach that if transabdominal ecchymosis is present, further intraabdominal injury is present until proven otherwise [10]. Appendix 1 is a list of the associated injuries that have been reported with typical Chance fractures. It is obvious that abdominal injury prevails because of the thoracolumbar location. In our patient, lung injury (contusion) supports the conclusion that associated injury occurs most commonly in the region of the greatest moment-force that collides suddenly with a fulcrum—the steering wheel in this case.
Although obvious protection and support are afforded the thoracic spine, enough force around a higher fulcrum (steering wheel) can, in fact, produce a flexion–distraction injury pattern in the upper thoracic spine. To our knowledge, no other Chance fractures of the upper thoracic spine have been reported, although this type of injury is relatively common in the lumbar spine. Injuries in the thoracic region will also have a different group of associated injuries and may have a greater degree of morbidity and mortality because of the thoracic anatomy and the close proximity of vital vascular structures.
As in the lumbar spine, the Chance fracture of the upper thoracic spine is a severe injury that has a characteristic fracture pattern. This flexion–distraction injury should indicate the need for meticulous evaluation of the supporting spinal ligamentous structures and should prompt a diagnostic search for other associated injuries. The injuries associated with Chance fractures will vary with anatomic location of the spine injury. This case shows that a Chance fracture may occur in the upper thoracic spine in addition to its more commonly described location in the region of the thoracolumbar junction.
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  M. P. Bernstein, S. E. Mirvis, and K. Shanmuganathan Chance-Type Fractures of the Thoracolumbar Spine: Imaging Analysis in 53 Patients Am. J. Roentgenol., October 1, 2006; 187(4): 859 - 868. [Abstract] [Full Text] [PDF]
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R. H. Daffner Chance Fracture of the Upper Thoracic Spine Am. J. Roentgenol., August 1, 2005; 185(2): 555 - 555. [Full Text] [PDF]
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