In vitro exposure to 0.5% bupivacaine is cytotoxic to bovine articular chondrocytes

Abstract

Purpose: Intra-articular use of 0.5% bupivacaine is common in arthroscopic surgery. This study was conducted to test the hypotheses that (1) 0.5% bupivacaine is toxic to articular chondrocytes, and (2) the intact articular surface protects chondrocytes from the effects of short-term exposure to 0.5% bupivacaine.

Methods: Freshly isolated bovine articular chondrocytes were prepared into alginate bead cultures and were treated with 0.5% bupivacaine solution or 0.9% saline for 15, 30 or 60 minutes, washed, and returned to growth media. Chondrocytes were recovered from alginate 1 hour, 1 day, and 1 week after bupivacaine exposure; they were fluorescently labeled to identify apoptotic and dead cells and were analyzed by flow cytometry. Twelve osteochondral cores were harvested from bovine knees. The superficial 1 mm of cartilage was removed from 6 cores (top-off). Intact and top-off cores were submerged in 0.9% saline or 0.5% bupivacaine solution for 30 minutes and then maintained in chondrocyte growth media for 24 hours. Live-cell/dead-cell fluorescent imaging was assessed using confocal microscopy.

Results: Greater than 99% chondrocyte death/apoptosis was observed in all bupivacaine-exposed alginate bead cultures compared with 20% cell death in saline-treated controls (P < .05). Osteochondral cores with intact surfaces treated with 0.5% bupivacaine showed 42% dead chondrocytes. When the articular surface was removed, 0.5% bupivacaine resulted in increased cell death, with 75% dead chondrocytes (P < .05).

Conclusions: Results show that 0.5% bupivacaine solution is cytotoxic to bovine articular chondrocytes and articular cartilage in vitro after only 15 to 30 minutes' exposure. The intact bovine articular surface has some chondroprotective effects.

Clinical relevance: Because healthy chondrocytes are important for maintenance of the cartilage matrix, chondrocyte loss may contribute to cartilage degeneration. This study shows a cytotoxic effect of 0.5% bupivacaine solution on bovine articular chondrocytes in vitro. Although these results cannot be directly extrapolated to the clinical setting, the data suggest that caution should be exercised in the intra-articular use of 0.5% bupivacaine.