How does a nerve block works or freezing the nerves in the back and r there any side effects to it. or nerve damage?

Sodium Molecules: Are prevented from flowing across nerve cell (neuron) membranes, stopping pain and nerve impulses from reaching the brain. Neuro-chemical release, however, is not affected! side effects, other than temporary loss of sensation, temperature awareness and movement are minimal. And, in the hands of experienced anesthesiologists, nerve injury exceedingly rare.

Na channel blocker: The local anesthetics work by blocking the sodium channels in the neruron preventing them from depolarizing and transmitting an electrical signal further to the nervous system. Thy are quite safe and have a very long history of use. The available preparations are not toxic to nerves. Nerve damage by physical trauma to the nerve by the needle has been reported but is very rare in experienced docs.

In simple terms: Local anesthetic blocks the transmission of messages from (and to) your body to your brain and spinal cord. Therefore there is no pain message being sent to your brain and thus, no pain experience while the medications are working. Spinal and epidural blocks have minimal risks but are, on the whole, very safe.