RSNA 2017: Understanding types of injuries caused by motor vehicle components
Knowing the types of injuries caused by components of a car, van, or bus can assist emergency radiologists focus imaging and expedite diagnoses of individuals injured in motor vehicle collisions. Specifically, once injuries are identified in a patient who has been hurt in an accident, the ability to predict the mechanism can help radiologists to identify subtle, more easily missed injuries.
Radiologists from Harborview Medical Center and the University of Washington Medical Center in Seattle described and illustrated different types of injuries resulting from motor vehicle collisions based on the mechanism of injury in a RSNA 2017 digital poster (ER-149-ED-X) that received a RSNA cum laude award. The poster reviews injuries caused by steering wheels, dashboards, floorboards, and seat belts as well as injuries from lateral impact inside the vehicle. Shaimaa A. Fadl, MD, a thoracic imaging fellow at the University of Washington, and co-authors also created an imaging checklist for each category.
Steering wheel injuries
When a steering wheel of a vehicle in an accident has been deformed, it is probable that the driver and front seat passenger may have serious thoracic and abdominal injuries. The greater the deformity of the wheel, the greater likelihood of injury to the passengers. Injuries may be less if a seat belt is in use at the time of the crash. The authors explain that as the passenger is thrust forward, the steering wheel and instrument panel is thrust backward and that the passenger(s) head may also hit the windshield, resulting in head and neck injuries. These may include complex facial fractures, orbital wall fractures, crushed tracheas, and possible thoracic spine hyperextension injuries in the cervical and thoracic spine.
Common thoracic injuries include rib and sternal fractures and aortic injuries. They are attributed to shearing stresses, osseous pinch, when the aorta is crushed between the sternum and spine, and to the water hammer effect, when blood tears the aortic wall. Solid organ injuries in the abdomen are common. Axial load injuries, such as distal radial fractures, occur when a passenger braces his/her head on a steering wheel or dashboard in an effort to brake impact.
Hip dislocation and knee injuries can occur from impact with a dashboard. The authors explain that when the force on a flexed leg is from the anterior, the femur is driven posteriorly. Direct impact to the patella can also result in patellar and distal mid-femur fractures. Radiologists should be alert to irregularity of the posterior acetabular wall, which is suggestive of fracture.
Anterior hip dislocation can occur. When the anterior force is directed against an externally rotated femur, the femoral head can be levered anteriorly from the acetabulum.
The most common knee injuries are tibial plateau fractures and ligamentous injuries. The latter occurs when the dashboard impacts the anterior tibia of the flexed knee, causing disruption of the posterior cruciate ligament (PCL), as one example. Tibial plateau fractures can result from impact of the femoral condyle on the tibial plateau when the driver’s leg is trapped between the floor and the dashboard.
Floorboard injuries include injuries to the metatarsals and tarsal bones. When the floorboard of a vehicle is driven upward into the ball of the foot, the energy of impact is transferred to these bones. Lisfranc and midfoot fracture-dislocation are common, as are ankle injuries. The authors explain that during plantarflexion and inversion, the talus strikes the articular surface of the tibial plafond resulting in talar dome fracture and that eversion and dorsiflexion will more likely fracture the lateral talar process.
Seat belt injuries
Radiologists should initially look for skin and soft tissue contusions caused by a seat belt, often called the seat belt sign. The presence of a seat belt sign indicates internal injury in approximately 30% of patients. This sign most commonly occurs over the anterior neck, breast, chest, and lower abdominal wall. The lap belt transverse contusion characteristically overlies the iliac bones. The authors write that a seatbelt sign can indicate serious internal injury, including lacerations or disruption of the recti muscles.
Seat belts can cause spinal injuries, such as flexion-distraction fractures and C7 and T1 transverse process fractures, as well as injury to the vertebral artery. Thoracic injuries include sternal fractures and mediastinal hematoma. The most common intraabdominal injuries include mesenteric tears and bowel ruptures.
Lateral impact injuries
The location and severity of lateral impact injuries are determined by size and location of door arm rests, height of side impact, and presence of a center console. They may encompass a victim’s head, chest, abdomen, pelvis and spine. The authors write that head injuries predominate in oblique impacts and thoracic injuries in perpendicular impacts.