#R4 IK
In terms of the exact degrees that is a very difficult question to answer, and
again it would depend on the level of accuracy you are looking for. There are
a number of very good references regarding joint motion if you are looking for
accuracy, if you are not looking for accuracy than as a general rule of thumb
each region of the spine acts about the same. Break up your vertebral column
into 3 sections, cervical, thoracic, and lumbar. Assign each section there
natural curve where the cervical spine has a lordosis, the thoracic spine has a
kyphosis and the lumbar spine has a lordosis. After you have set up those
curves than looking at each individual vertebrae per section rotation can be
set that the vertebrae does not override the articular facet joint. In terms
of flexion and extension, with flexion you will have to make sure that you can
flex only to the degree that you do not put the anterior portion of the
vertebral body into the other and you will have to compress the disc in
proportion to the amount flexed. In extension make sure that the spinous
process's don't run into one another. If you want to be absolutely precise,
very, very tough I will again refer you to the 3 volumn set on biomechanics by
Kapnji, if you want something more concise, if you have access to a medical
library do a medline search focusing on the journal SPINE with the keywords
vertebrae, and range of motion. That should get you started. Sam