PHTLS Kinematics of Trauma 1 — Questions and Answers
Question 1: According to Newton's first law as it applies to trauma, what happens to an unrestrained occupant when a vehicle suddenly stops?
- The occupant stops simultaneously with the vehicle
- The occupant continues moving at the same speed until acted upon by another force (Correct answer)
- The occupant slows gradually due to friction
- The occupant is pushed backward by the seat
Correct answer: The occupant continues moving at the same speed until acted upon by another force
Newton's first law states that an object in motion stays in motion; an unrestrained occupant continues forward at the pre-impact speed until struck by the dashboard, steering wheel, or windshield.
Question 2: The kinetic energy formula used in PHTLS to estimate energy transfer during trauma is:
- KE = mass × velocity
- KE = ½ × mass × velocity² (Correct answer)
- KE = mass × gravity × height
- KE = force × distance
Correct answer: KE = ½ × mass × velocity²
KE = ½mv² demonstrates that velocity has a squared effect on kinetic energy, meaning doubling speed quadruples the energy that must be absorbed by body tissues.
Question 3: In a frontal-impact motor vehicle collision, which injury pattern is associated with an unbelted driver who travels 'up-and-over' the steering wheel?
- Lumbar spine compression and hip fractures
- Head, neck, thorax, and face injuries (Correct answer)
- Posterior rib fractures and renal contusions
- Bilateral femur fractures and knee dislocations
Correct answer: Head, neck, thorax, and face injuries
The up-and-over pathway directs the body toward the steering wheel and windshield, commonly causing head, facial, cervical spine, and thoracic injuries.
Question 4: Which injury pattern is most characteristic of the 'down-and-under' pathway in a frontal motor vehicle collision?
- Facial lacerations and basilar skull fracture
- Knee, femur, hip, and posterior acetabulum fractures (Correct answer)
- Aortic tears and pulmonary contusions
- Cervical spine hyperextension injuries
Correct answer: Knee, femur, hip, and posterior acetabulum fractures
In the down-and-under pathway the knees impact the dashboard, transmitting force up the femur to the hip and posterior acetabulum, producing a predictable lower-extremity and pelvic injury pattern.
Question 5: A patient was a restrained driver in a rear-impact collision. Which injury is most predictable based on kinematics alone?
- Sternal fracture
- Hyperextension cervical spine injury (Correct answer)
- Splenic laceration
- Bilateral pneumothorax
Correct answer: Hyperextension cervical spine injury
Rear impacts cause rapid forward acceleration of the torso while the unsupported head lags behind, producing hyperextension stress on the cervical spine.
Question 6: What does 'index of suspicion' mean in the context of PHTLS kinematics?
- The probability that the patient is lying about the mechanism
- Anticipating likely injuries based on the mechanism of injury even before they are confirmed (Correct answer)
- A scoring system for scene safety threats
- The likelihood of a secondary explosion at the scene
Correct answer: Anticipating likely injuries based on the mechanism of injury even before they are confirmed
Index of suspicion means maintaining awareness of probable injuries predicted by the energy exchange and mechanism so treatment is not delayed waiting for symptoms to manifest.
Question 7: Which type of tissue absorbs the most kinetic energy during blunt trauma, making it most susceptible to injury?
- Low-density tissue such as lung
- High-density tissue such as solid organs and muscle (Correct answer)
- Fatty tissue such as subcutaneous fat
- Hollow viscus with gas such as bowel
Correct answer: High-density tissue such as solid organs and muscle
High-density, inelastic tissues such as solid organs and muscle cannot deform as readily and therefore absorb more energy per unit volume, resulting in greater injury.
PHTLS Kinematics of Trauma 1
According to Newton's first law as it applies to trauma, what happens to an unrestrained occupant when a vehicle suddenly stops?