Epidural steroid injections ( Figure 47–23) are used for symptomatic relief of pain associated with nerve root compression (radiculopathy). Pathological studies often demonstrate inflammation following disc herniation. Clinical improvement appears to be correlated with the resolution of nerve root edema. Epidural steroid injections are clearly superior to local anesthetics alone. They are most effective when given within 2 weeks of pain onset but appear to be of little benefit in the absence of neural compres-sion or irritation. Long-term studies have failed to show any persistent benefit after 3 months, and these injections may change the time course of pain relief without changing long-term outcomes.
The two most commonly used agents are meth-ylprednisolone acetate (40–80 mg) and triamcino-lone diacetate (40–80 mg). Dexamethasone is being used with increased frequency due to its smaller particulate size (smaller than an erythrocyte). Intravascular injection of steroid suspension with larger particulate size may lead to embolic compli-cations. The steroid may be injected with diluent (saline) or local anesthetic in volumes of 6–10 mL or 10–20 mL for lumbar and caudal injections, respec-tively. Simultaneous injection of opioids offers no added benefit and may significantly increase risks. The epidural needle should be cleared of the ste-roid prior to its withdrawal to prevent formation of a fistula tract or skin discoloration. Injection of local anesthetic along with the steroid can be help-ful if the patient has significant muscle spasm, but it is associated with risks of intrathecal, subdural, and intravascular injection. The presenting pain is often transiently intensified following injection, and the local anesthetic provides immediate pain relief until the steroidal antiinflammatory effects take place, usually within 12–48 h.
Epidural steroid injections may be most effec-tive when the injection is at the site of injury. Only a single injection is given if complete pain relief is achieved. If there is a good but temporary response, a second injection may be given 2–4 weeks later. Larger or more frequent doses increase the risk of adrenal suppression and systemic side effects. Most pain practitioners utilize fluoroscopy for epidural injection and confirm correct placement with injec-tion of radiopaque contrast ( Figures 47–24 through 47–26). A transforaminal epidural steroid injectionmay be more effective than the standard interlami-nar epidural technique, especially for radicular pain. The needle is directed under fluoroscopic guidance into the foramen of the affected nerve root; contrast is then injected to confirm spread into the epidural space and absence of intravascular injection prior to steroid injection. This technique differs from a
selective nerve root block (SNRB) in two important ways; with an SNRB, the needle does not enter the foramen and the injected solution tracks along the nerve but not into the epidural space. The SNRB may be helpful as a diagnostic procedure for the surgeon who is considering a foraminotomy at a particular affected level based upon imaging, clinical presenta-tion, and the results of the SNRB.
Caudal injection may be used in patients with previous back surgery when scarring and anatomic distortion make lumbar epidural injections more difficult. Unfortunately, migration of the steroid to the site of injury may not be optimal. The use of a catheter to direct the injection within the sacral and epidural canal may improve outcome. However,above the level of S2, there is a risk of thecal perfora-tion with a stylet-guided catheter. Intrathecal steroid injections are not recommended because the ethyl-ene glycol preservative in the suspension has been implicated in arachnoiditis following unintentional subarachnoid injections.