The purpose of a collar is to prevent ranges of motion outside of limits deemed unfavorable for fracture healing.
A fracture that is deemed to be stable may be treated with a collar immobilization or without immobilization.
Early mobilization is instituted once a patient is upright. AP lateral plain x-rays are then obtained to make sure there is no significant fracture displacement requiring surgery.
The Philadelphia collar is used for the initial conservative treatment. It provides more stability than the hard collar.
If follow up X-ray show no displacement after 2 weeks, one can change to the hard collar for patient comfort.