In the current study, we evaluated disc degeneration over a five year period in patients who had received either discography or discoblock (injection of bupivacaine) and compared the results with control subject. Compared to the control or discography group, bupivacaine injection group did not show accelerated disc degeneration. We concluded that there was no toxic effect of bupivacaine to intervertebral disc based on radiographic and MRI study.
Bupivacaine has been found to be chondrotoxic in vitro
, and several studies have shown a dose- and time-dependent chondrotoxicity of local anesthetics [6-8
]. Furthermore, an effect of 0.5% bupivacaine on disc cells and articular chondrocytes in vitro
has been reported [9
]. Rabbit and human disc cell death demonstrated a time and dose dependence in response to bupivacaine [9
]. Moreover, cell death was greater than that observed for articular chondrocytes [9
]. These reports indicated that 0.5% bupivacaine had an apparent toxic effect on disc cells and articular chondrocyte of animals and humans in vitro
]. Wang et al. [11
] also reported an in vitro
study that harmful effects of bupivacaine on several cell types, including nucleus pulposus and annulus fibrosus cells, both in cell and disc organ models. And bupivacaine negatively impacts disc cell viability and matrix metabolism, both of which strongly correlate to intervertebral disc degeneration.
An effect of 0.5% bupivacaine on articular chondrocytes in vivo
has been reported; however, the effect was somewhat different from data obtained by in vitro
]. Rats received a 0.5% bupivacaine into the knee joint and were observed during 6 months. In vivo
study showed a significant reduction in chondrocyte density 6 months after a single intra-articular injection of 0.5% bupivacaine. This result was in agreement with in vitro
study of rat cells [12
]. However, the articular surfaces of bupivacaine-injected joints remained intact on gross and histological evaluation. The authors of that study concluded that potential toxic effects of bupivacaine may exist following a single injection, but that this would be difficult to detect clinically [12
In this study, there was no significant difference in disc degeneration at 5 years following bupivacaine injection according to the evaluation using Pfirrmann's classification. Furthermore, there was no significant difference in disc height, range of motion, or translation between flex and extension position. There is a possibility that cell death and toxic effects had occurred in the disc of the patients who had received discoblock; however, this change does not appear to be clinically and radiographically relevant. Further study is needed to clarify the toxic effect using high sensitivity MRI or biopsy.
Additionally, there was no significant difference in progression of disc degeneration between control and discography groups at 5 year follow-up. Carragee et al. [13
] recently reported that modern discography techniques using small gauge needles and limited pressurization resulted in accelerated disc degeneration, disc herniation, loss of disc height and signal, and the development of reactive endplate changes compared with matched-controls at 10-year follow-up [13
]. This apparent difference may be because of differences in the number of patients and follow-up periods. Further longer-term follow-up is needed to clarify this point.
This study has several limitations. First of all, we have examined a small number of patients in each group. Second, the average age of the patients was around 35-year-old, however, the average of disc degeneration was from 3.7 to 3.8 before examination. grade V change has occurred in 10 patents in all patient 5 years after examination. In this study, the patient's population tended to show more severe degeneration of disc. Finally, a single or multiple injections of bupivacaine, the volume of bupivacaine, concentration, degenerative stage of the disc to be injected, and how the injection was given were not examined in the current study. A follow-up study with a larger number of patients and dose-dependent measurements of bupivacaine is needed to validate the findings from this study.