Quantification of neural tissue injury in a rat radiculopathy model: comparison of local deformation, behavioral outcomes, and spinal cytokine mRNA for two surgeons

Clinical and experimental work indicate that a variety of factors contribut e to radicular pain mechanisms, including mechanical injury. While it has b een qualitatively suggested that the magnitude of nerve root mechanical inj ury affects the nature of the pain response, no study has quantified the lo cal in vivo injury biomechanics in these models. Therefore, it was the purp ose of this study to develop and implement an in vivo method to quantify co mpressive nerve root injury strain severity and characterize its effect on the resulting responses in an existing lumbar radiculopathy rat model Male Holtzman rats were divided into a sham group with only nerve root exposure or a ligation group with the nerve root tightly ligated using silk suture. Using image analysis, nerve root radial strains were calculated at the time of injury for two surgeons. Mechanical allodynia was continuously assessed throughout the study and spinal cord cytokine mRNA levels were assayed on postoperative day 7. The degree of intersurgeon variability for imposing a ligation injury in this model was also assessed. Mean compressive injury st rains in the nerve root were 32.8 +/- 14.2% and were not different for the two experimenters. Animals undergoing more severe ligation strains exhibite d significantly heightened allodynia following injury and greater upregulat ion of the inflammatory cytokines IL-1 alpha/beta, IL-6, and IL-10. Results indicate a direct correlation of local nerve root injury severity with the ensuing physiologic responses associated with nociception. (C) 2001 Elsevi er Science B.V. All rights reserved.