Whiplash Injuries

Whiplash injuries are injuries to your neck when you’ve had a car accident. Car accidents that cause neck pain are really common, as they happen about 5 million times a year in the United States. Sometimes they are mild, and too many times, they can be disabling.

Your doctors have probably been traditionally well-trained in pathological conditions that happen in your neck, but they might not have been very well trained in motor vehicle collisions and how they can affect your neck. They might not understand how they happen, how to diagnose them, how to manage them, and what to tell you for a prognosis. Further, they might not know much about litigation–the med-legal part of the injury.

Personally, I have been a victim of a rear-end collision a few times in my life. The first happened while I was in high school. A car hit the back of my 1981 Buick Regal, and I in turn, hit the car in front of me. As a kid, I liked to recline my car seat a little bit too much, which is probably not very wise in hindsight, but that might have saved me from having a lot of neck trauma. The second time, I was in a small sports car in about 2005, and I was hit from behind by an SUV. I made it out okay with that one too, but I might have been pretty sore the week following the injury. The third time, I have been hit from behind was in 2018, and at the time of this writing, I am still sore from  the injury. I was at a complete stop on Highway 37 in Sonoma at Sears Point in my Prius when a kid in an SUV/Minivan hit me with enough force that I remember being propelled into the pickup in front of me. All of this collision happened in a blink of an eye.

Vehicle Dynamics

A car crash is a very brief event. They only last about the blink of an eye. 100 milliseconds. Your neck muscles only respond in about 200 milliseconds, which can cause problems that I will talk about later.

When you hit someone from the front, there are three ways that the energy from your speeding vehicle absorbs the speed and energy from your car:

  • The first crush zone is the area between your bumper and the car’s engine.
  • The engine compartment absorbs the energy next, and this part is much stiffer than the bumper crush zone.
  • The structures behind the engine, but in front of the firewall where your dash board is mounted is the third area of impact absorption, and this is less stiff than the engine compartment, but stiffer than the bumper.

If you are the driver of the “bullet” car, your body will continue to move along at the speed you were traveling while your car is crushing in these three zones. Until it is caught in your seatbelt or airbag. Or windshield or steering wheel.

A body in motion will stay in motion until acted upon by another force.

As your car suddenly stops against the car in front of it, you have about 4-18 inches of wiggle room until your body meets the seatbelt in front of you, or another part of the car. Women can have worse injuries than men because women tend to have their seats pulled farther forward, and places their bodies closer to the steering wheel and other interior car bits. Either way, your seatbelt will be the first point of contact, and the largest source of direct blunt injury to your body.

If your body hits parts of the car’s interior, you will have a direct blunt trauma to a body part. In your neck, though, you’ll get a sprain/strain type of injury.

Side Impact

About a third of all car accidents are side impact injuries. Same crash time: 100ms. In most cars, when you are hit, you have 8-12 inches of car door and space before the impact hits your body, and the peak time for injury happens at 35ms. The side impact will compress your car’s suspension on the far end, which can lift your car at the point of impact. If you are hit from the side, your torso will load at the side of the collision and your head will lag behind, leaving you with jammed neck joints, and strained neck muscles.

There’s no bumper and engine to absorb these kinds of injuries, so they can be pretty devastating. When it comes to your neck, the most commons part of the neck that gets injured is at C5-C6. The discs in your neck are primarily injured, followed by the facet joints, then your muscles. If you are sitting in the side of the car closer to the impact, you will get injured more than if you were sitting on the other side. You’ll have 1-3 times more risk of injury.

High Speed Rear End Collisions

“High Speed” rear enders are classified as such when the car’s speed is more than 10 miles per hour. Most research on rear end crashes study 2 to 5 mph collisions.

As a rear-end collision occurs, the energy of the crash is absorbed by both the bullet car, and the target car. Sometimes the target car will absorb the impact through the back hatch or trunk. Sometimes the bullet car will absorb impact through the hood. Usually the impact will submarine the suspension of the target car.

As the collision’s forces travel through the frame of the car, the person sitting in the target car will slam into the back of their seat as the seat travels forward with the collision. The forces push your seat back into your mid-back. Your torso pushes forward, leaving your neck behind, then your neck finally catches up by either hitting the head restraint (head rest), or by a shearing force in your neck.  If your neck has to absorb the crash energy, then your neck structures will have to bear the trauma. Discs, facets, ligaments, and muscles will have to be injured as your 12-16 pound head is pulled forward.

If this injury is severe enough, and if you’re lucky, then the pin that secures your seat back will break, and your seat back will break away, absorbing more energy, and causing you to recline as the impact slows down (decelerates.) In some cases, a broken seat will let you walk away from a crash without injury1.

A rebound often occurs. After the first impact has caused you to spring off of the back of your seat, you could hit the steering wheel or dash board, and you could be further injured. This happens in 28 percent of all injuries2.

Neck Injuries in High-Speed Crashes

Your neck gets injured by your seat back punching your back, and your head moving backward. Your head might hit the head restraint, or if your car’s seat if designed poorly, it will pitch up and over the head restraint, pushing it down into it’s low position. In old pickup trucks, your head will hit the rear window.

Then you rebound, and your head moves forward. Maybe your head will hit something, or maybe your neck joints will absorb the impact.

One study shows that when your seat back hits your mid back, it causes your spine to compress at the junction between your neck and upper back. Your mid back gets taller, and it compresses the discs in your neck, creating an injury.

There have been many studies on low-speed collisions on humans, for safety, and it’s been said that you can take the low speed results and magnify them the faster the collision is.

Here are the factors for injury:

  • Head turned
  • Seat back stiffness
  • Elastic rebound of the seat back
  • Female passenger (smaller neck to support the head, compared to men)
  • Different car models
  • Being unaware of impact
  • Being too tall
  • Being too short
  • Being out of position
  • Being elderly
  • Movable head restraints (as opposed to fixed, like in a Volvo or Porsche)
  • The car does not crumple, stays undamaged on the bumper
  • Change of velocity of the target car (does it get thrown forward very far?
  • Small car hit by large truck
  • Pre-existing medical conditions (osteoarthritis, disc degradation, thyroid disorders, spinal surgery, spinal stenosis, diabetes)

Next: Clinical Presentation of Whiplash Injuries


Morris A, Thomas P. Neck Injuries in the UK Co-operative Crash Injury Study. SAE. 1996;(962433).
Farmer C. Effects of Head Restraint and Seat Redesign on Neck Injury Risk in Rear-End Crashes. Traffic Injury Prevention. 2010:83-90.

Published by Todd Lloyd

Dr. Lloyd is a chiropractor in San Francisco. He maintains an active interest in treating neck and shoulder pain and dysfunction.

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