First, a brief anatomy lesson. The spinal cord travels from the base of the brain, down the spinal canal, and is surrounded by spinal fluid. Encasing the spinal fluid is a sac called the DURA (simplified). Surrounding that sac is a space called the epidural space [(Epi - on top of) + DURA = EPI-DURAL]. This space has been used in the practice of medicine for decades to provide many forms of treatment, most commonly for pain relief (labor epidural analgesia, surgical anesthesia, post-surgery analgesia, and single shot injections for chronic pain). The effective difference depends on the technique used and the type of medication that is injected, as well as whether or not a catheter is left in the epidural space.
Medications are injected via the needle or through a small, flexible catheter. The needle/catheter is then removed, dressing placed and the patient is then monitored for some time to ensure that there is no adverse reaction to the medication. The medication generally used is a combination of local anesthetic and "cortisone" type medication. There is minimal pain involved in the procedure. The procedure is considered safe, such that it can be performed in the office setting by specialists. There is very little to no "down time". The patient may return to regular activity the following day.
In the treatment of chronic pain, a catheter may or may not be used but, generally no catheter is left in the epidural space if the patient is not hospitalized. The epidural procedure is generally performed in an outpatient setting under fluoroscopy (motion x-ray), using sterile technique in the prone (lying on abdomen) position. The skin overlying the location of the injured or arthritic area is numbed using a local anesthetic. A specialized needle is then used to enter the epidural space. The doctor has many ways of confirming proper placement of the needle, including fluoroscopy.