The Effect of Epidural Injection of Betamethasone or Bupivacaine in a Rat Model of Lumbar Radiculopathy

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Abstract
The effect of epidural injection of betamethasone or bupivacaine was investigated in an animal model of lumbar radiculopathy. To investigate the effects of an epidural steroid (betamethasone) or a local anesthetic (bupivacaine) in an animal model of radiculopathy produced by nerve root irritation. Epidural injections are commonly used for the treatment of low back pain and sciatica. However, efficacy remains controversial, and there is a paucity of basic information to support clinical use or the injections. Fifty-one rats were used. The left L4 and L5 nerve roots were loosely ligated with chromic gut, and either betamethasone, bupivacaine, betamethasone in combination with bupivacaine, or saline was injected using an epidurally placed catheter. The effects of epidural injection were evaluated using response to noxious stimuli and immunohistochemical methods. In betamethasone-treated rats (either alone or in combination with bupivacaine), thermal hyperalgesia was significantly less (P < 0.01) after surgery than that in saline- or bupivacaine-treated groups, in which the hyperalgesia was maximum at 2-3 postoperative weeks before resolving 5 weeks after surgery. Immunohistochemical analysis did not correlate with these results. Epidural steroid injection has a significant effect on the thermal hyperalgesia produced in a model of radiculopathy, which may provide clinical support for advocates of epidural steroids.