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Originally Posted by MAD
Sorry, I was referring to the damage to the car. The way it was written was like "it's only a little bit of whiplash".
Are you referring to a straight on impact (compression)? Are compression fractures, in the neck, common for an unhelmeted victim?
I was thinking more along the lines of an incident that places the head in a position where it applies significant leverage to the neck. Not a straight on impact.
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I was referring to to both. Direct force trauma is injury at the point of the body that has struck something else (eg skull fracture at the point of impact), indirect force trauma is injury at an area remote as a result of transfer of forces (such as neck fracture from trauma to the head). By reducing the force applied to the head (through absorption and increasing the duration of the force) you reduce both the severity of direct force trauma and the severity of indirect force trauma.
Compression (or blow out) fractures of the neck are common in any incident that applies significant force to the top of the head in line with the longitudinal plane of the vertebrae. Although prevalent in bike accidents, particularly in over the handlebars accidents, it is more common in diving accidents and contact sport spear tackles. This injury mechanism is less likely to cause spinal cord damage in the initial injury event, further movement can cause injury though. It is hyperflexion (bending head down) hyperextesnion (bending head up) or hyperrotation (turning head beyond normal range) that tend to cause neck fractures with spinal cord damage. These injury patterns occur when force is applied to the head/neck in a plane perpendicular or offset to the plane of the spinal column, in other words a side shearing force. This type of injury can occur in head trauma resulting from car accidents (e.g head into B pillar on side impact), bike accidents (fall sideways, forwards or backwards and side, front or rear of head on ground) or assaults (e.g hit to front, rear or side of the head with a baseball bat). Severe whiplash (hyperflexion followed by hyperextension) in car accidents etc will also cause this type of injury but this has been pretty much made a thing of the past by the widespread use of head rests (stops the hyperextension).
Welcome to severe head/spinal trauma 101, the important point to take away from it is that any shock absorption will reduce the energy applied and therefore the risk and severity of injury. That is simple physics and can not be disputed. How much energy is required to cause serious injury, any fall or force directly to the head that equates to more than a fall from standing level is of great risk (in some such as infants and elderly less force than that is required). So a fall from a bike traveling at just 15 km/h (that is absolutely snail pace) resulting in a direct blow to the head is sufficient to cause significant and life threatening head and spinal trauma.
I hope that helps dispel the myth that falls from bikes at low speed without helmets are unlikely to cause serious injury. The truth of the matter is sometimes low speed can make you more prone to crash because of the lack of perceived risk and therefore a lack of concentration. Ask any competitive cyclist what speed most of their falls happen at and they will probably say low speeds when they aren't paying attention. Most of the bike crashes I go to at work happen at low speed intersections, crossings and high pedestrian areas etc. The more speed you have at the time, the more you think about what you are doing because of the higher perceived risk, it is human nature.