COMPARATIVE LOCAL-ANESTHETIC BLOCKS IN THE DIAGNOSIS OF CERVICAL ZYGAPOPHYSIAL JOINT PAIN

The utility of randomised, double-blind, controlled, comparative local anaesthetic blocks for the diagnosis of cervical, zygapophysial joint pain was studied in 47 patients with chronic neck pain following whip lash injury. Each patient was investigated with radiologically control led blocks of the medial branches of the cervical, dorsal rami to anae sthetise the target cervical, zygapophysial joint. The blocks were per formed using either lignocaine or bupivacaine, randomly allocated, and the patients' responses were assessed in a double-blind fashion. Any positive response was subsequently assessed by repeating the block wit h the complementary anaesthetic. Only those patients experiencing a lo nger period of pain relief from the bupivacaine were considered to hav e true-positive responses. Forty-four patients had pain relief from tw o blocks at a single level, of whom 34 had longer pain relief from bup ivacaine. This result is unlikely to have occurred by chance (P = 0.00 02). The durations of pain relief obtained from the anaesthetics were consistent with the known characteristics of these drugs with bupivaca ine lasting significantly longer than lignocaine (P = 0.0003). A subgr oup of 13 patients were identified with unexpected, prolonged response s to one or both of the anaesthetics. Comparative, diagnostic blocks a re a valid technique in the identification of painful zygapophysial jo ints, and constitute an implementable alternative to normal saline con trols.