The pars defect as a pain source. A histologic study.
STUDY DESIGN: Tissue from the pars defects of six adult patients with symptomatic spondylolysis and spondylolisthesis was obtained at surgery. A histologic study was conducted to identify and characterize neural elements in this tissue. OBJECTIVES: To determine if nociceptive nerve endings were present within the pars defect of patients with symptomatic spondylolysis. SUMMARY OF BACKGROUND DATA: The origin of back pain in patients with spondylolysis remains uncertain. The defect in the pars interarticularis has been implicated as a possible pain source. METHODS: The soft tissue from the pars defect was obtained at surgery. A modified gold chloride stain was used to prepare the tissue for histologic examination. Tissue blocks were sectioned and studied under light microscopy. RESULTS: Neural elements were found in all specimens examined. Free nerve endings believed to have nociceptive function were identified in all specimens. The density of neural elements varied between specimens. CONCLUSIONS: The finding of neural elements, including free nerve endings within the pars defect tissue, suggests that the pars defect may be a source of back pain in some patients with symptomatic spondylolysis.