Peridural Fibrosis Associated with Postoperative Allodynia, but not Neurological Dysfunction in a Rodent Model

Failed back surgery syndrome (FBSS) is a prevalent, debilitating condition that affects the quality of life of many patients. The role of peridural fibrosis in FBSS continues to be a source of controversy. The authors report an association between peridural fibrosis and tactile allodynia, but not neurological dysfunction in a rodent cauda equine crush injury model. Methods Twenty-one rats were equally divided into three different treatment arms: 1) sham, 2) laminectomy-alone, and 3) laminectomy plus cauda equina crush injury. Tactile allodynia was tested and open field locomototor testing was completed according to a predetermined schedule. Animals were sacrificed on postoperative day 42. Histological sectioning was used to determine the degree of peridural fibrosis present in each group of animals. Results Animals who underwent greater surgical manipulation showed greater degrees of peridural fibrosis on histological analysis. Animals in group 3 showed significantly more allodynia at all time points during the study. Laminectomy animals showed more allodynia than sham animals, but less than crush injury animals. Locomotor function was worse in laminectomy-only animals on post-operative days 8 and 15, compared with sham animals. Locomotor scores improved thereafter to that of sham animals. Crush injury animals remained functionally impaired through the duration of the study. Histological analysis demonstrated greater degrees of peridural fibrosis in laminectomy and crush injury animals, as compared with sham. Conclusions Greater degrees of tactile allodynia were demonstrated in rodents with more surgical manipulation. Alternatively, neurological function, as measured by open field locomotor testing, was unaffected in laminectomy-only animals, though tactile allodynia remained worse compared with sham animals. Histological analysis qualitatively demonstrated an association between degree of surgical manipulation and peridural fibrosis. Peridural fibrosis, although associated with greater degrees of allodynia, did not appear related to neurological injury.