Evaluation of the Time- and Dose-dependent Cytotoxic Effects of Lidocaine on Bovine Nucleus Pulposus Cells in vitro

Introduction: The aim of this study was to study if lidocaine exhibits a toxic effect on bovine-derived nucleus pulposus (NP) cells in an in vitro study. Provocative discography is utilized by some physicians in the evaluation of back pain that may be discogenic in origin, and some variations of the technique suggest infiltration of lidocaine into the outer anulus fibrosus prior to intradiscal injection of contrast agent. In the evaluation of morphologically normal discs adjacent to abnormal discs, some practitioners utilize intradiscal lidocaine to block the abnormal disc prior to evaluation of the adjacent level. There have been recent reports noting a toxic effect of lidocaine and bupivacaine to articular chondrocytes. Although the mechanism has not been fully described, prior studies have indicated a tight coupling between the ionic channels of chondrocytes and proliferation. In contrast to diarthrodial joints with vascularized synovium, the intervertebral disc relies completely on diffusion for nutrient transport. Consequently, it is hypothesized that any intradiscal injection of anesthetic will have a significantly greater residence time, as both metabolism and clearance will be markedly slower. Nucleus pulposus cells remain to be completely characterized in terms of phenotype and cellular markers. Although NP cells are a distinct cell population, they do share many phenotypic traits with chondrocytes, and consequently, there is reason for concern regarding possible lidocaine toxicity.