The nerve roots in your spine are covered by the dura. The sleeve-like space that surrounds the dura is known as the epidural space.
An epidural injection places anti-inflammatory medicine (i.e. cortisone) into the epidural space to reduce nerve inflammation, and hopefully reduce the severity of the symptoms. Although not always helpful, epidural injections reduce pain and improve symptoms in most people within 3-7 days.
Even though epidural injections may not always be a permanent fix, allowing certain periods without pain can be of great benefit and may augment other techniques.
Physical therapy may be more effective in concurrence with epidural injections since less pain means a superior therapy session.
Remember, injections are not the best treatment for all pain types. Even when they are appropriate, they are usually more effective as part of a more comprehensive treatment strategy.
Depending on the circumstances, the destruction of the nerve (as opposed to temporary numbing through a local anesthetic) could be considered. This is referred to as a rhizotomy.
Aside from the obvious complications of nerve destruction, permanently damaging a nerve may inadvertently and inevitably damage the soft tissue adjacent to that nerve as well.