Failed Back Surgery Syndrome (FBSS) is commonly encountered in
pain-treatment settings in the United States. We tested whether potential key factors in this syndrome, such as extracellular concentrations of
excitatory amino acids (EAAs), are increased in the dorsal horn by synaptic release due to unintentional stretch and/or deformation/compression/transection of dorsal spinal structures during surgery. We hypothesized that pharmacological
nerve block as a form of preemptive
analgesia prior to any insult to dorsal root neurons will prevent an abnormally high increase in extracellular concentrations of EAAs in the dorsal horn and ultimately the establishment of central sensitization during back surgery. The L4 and L5 dorsal roots were cut bilaterally near the spinal cord to provide an adequate model to test for preemptive
analgesia.
Amino acid concentrations were measured by dorsal horn microdialysis sampling; EAAs
aspartate and
glutamate were significantly increased by 80% and 65% respectively, as were other
amino acids compared to
sham control values. Topical application of 1%
Lidocaine, a voltage-gated Na(+) channel blocker, for 10 min prior to L4 and L5 bilateral dorsal
rhizotomy (BDR) significantly attenuated the increase in EAA concentrations such that their values were not different from
sham controls. Behavioral tests demonstrated significant hindlimb
mechanical allodynia after BDRs that was significantly attenuated by
Lidocaine pretreatment. Thus,
Lidocaine pretreatment could offer a safe measure for prevention of
chronic pain for back
surgical procedures if given by
intramuscular injection,
topical administration onto spinal nerves and/or the dorsal spinal surface during
surgical procedures that include
nerve entrapment release, intervertebral disc modification and
laminectomies.