It’s estimated that as many as one million Americans experience a whiplash injury each year with many occurring as the result of rear-end collisions. While many whiplash patients do recover, a large percentage will experience ongoing symptoms that can persist for years or even lead to some degree of permanent disability. This is partly the result of the unique series of events that occur when the head and neck are accelerated and decelerated at speeds and forces too fast and great to protect against. Let’s take a look at the phases of motion that take place during a whiplash event.

Pre-Collision: Prior to impact, the occupant sits in a vehicle with their mid back (thoracic spine) resting on the seat back and the head upright with a properly positioned head rest just behind it. The neck (cervical spine) assumes its normal physiologic shape of lordosis, or a “C” shape, when viewed from the side of the body.

Retraction Phase: Initially, the seat back is rapidly pushed forward into the thoracic spine of the occupant as the vehicle accelerates forward due to the impact. Based on the incline of the seat back and its springiness, the normal thoracic spinal curvature flattens and ramps up the seat back creating axial compression and lower cervical (neck) flexion as the weight of the head (about twelve pounds) translates backward relative to the torso producing an “S” shaped cervical spine. This aberrant, non-physiological, uncontrolled motion occurs within a very short timeframe of 0.05–0.20 seconds—too quick for the muscles to contract in a protective fashion. This cervicocranial motion can injure the cervical facet joints (the joints in the back of the spine) as well as the ligaments and disks in the front of the spine.

Extension Phase: As the thoracic spine continues forward, the cranium, tethered by the cervical spine, starts to rotate and the spine moves into full extension. The “S” shape of the retraction phase gives way to an exaggerated physiological extension “C” curve as the head nears the head-restraint. Here, shear forces across the cervical segments increase tension and compression as the cervical spine reaches the “C” curve position. The movement of the head backward should be stopped by the head rest, but if the seat back is too far reclined or the head rest is too low, the head can continue to move backward. At this point, the muscles supporting the head and neck should begin contracting in response to the collision.

Rebound Phase: Here, the over-stretched anterior (front) cervical musculature contract, moving the head and neck forward into flexion. The thoracic spine’s forward motion is often limited by the seat belt locking, leading to further cervical flexion and rotation (due the angled chest restraint). During this phase, eccentric contractions of the posterior cervical musculature occur, and this is thought to be the mechanism for posterior neck muscle injury during rear-end crashes. The greatest injury potential is thought to arise during this phase—especially when the head restraint is improperly positioned (too far from the head).

Doctors of chiropractic are well-versed in managing patients with whiplash injuries, often with a multimodal approach that includes manual therapies, traction, physiotherapy modalities, neck-specific exercises, and more.