What is SBS?
How is it caused?
by Staff 7.10.2007
Babies are vulnerable to injury during a shaking eipisode for three main reasons:
1) They have relatively large heads compared to their bodies at this age;
2) They have very weak neck muscles that cannot control or lessen the movement of their head during shaking; and
3) The person doing the shaking is so much bigger and stronger than the infant.
Shaken baby syndrome occurs when an infant or young child is shaken violently and repetitively with or without impact. The forces that work on the brain during shaking are much different than the forces that occur during a fall. The baby?s head whips back and forth at a high speed several times per second. This whipping motion creates an acceleration and then a deceleration force inside the baby's head every time it moves back and forth. These forces are thought to increase in strength with each shake.
The infant's brain is not fully developed and has a very soft consistency like unset gelatin. It mainly consists of a watery substance that can easily be distorted. The brain is covered by a skull that is thin and hard. There are blood vessels that supply the brain with oxygen and other materials called bridging veins. It is usually these veins that stretch and tear during a shaking episode. This causes bleeding and/or swelling of the brain and may lead to serious damage.
It is not yet clearly defined how little shaking is needed to produce brain damage as factors such as the age of the victim, the strength of the perpetrator and the presence or absence of impact would have to be considered. However, it is known that VIOLENT and SUSTAINED shaking at an estimated 2 - 4 cycles per second will cause injury. A shaking episode can last less than 4 seconds to as much as 20 seconds or more. In most cases, it is thought the period of shaking is about 5 to 10 seconds, just long enough for the caregiver to realize what they are doing.
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