I chose the vertebra body as target and the disc was chosen as a contact. Because the young's modulus of a vertebra is larger than the disc's young's modulus. 

The body was chosen as target and the disc was taken for the contact.

Here, the details of the contacts are given in the photo.

Details of contacts


When I initialize the contact tool all the results of information had the orange color legend. Initial Contact tool information


Here is the photo of my model. 

Full model


I chose the disc of Lumbar 5 as fixed support.

 Fixed support


And the force was given on atlas. ( -20 N force was applied in the y-direction).

Applied Force

Here the details of force are given. 

Details of force