The effect of local anesthetics administered via pain pump on chondrocyte viability

Abstract

Background: Chondrolysis initiated by postoperative, intra-articular pain pumps has recently been described by multiple institutions.

Purpose: To evaluate the in vitro chondrotoxicity of anesthetic formulations commonly used in pain pumps.

Study design: Controlled laboratory study.

Methods: Freshly isolated human articular chondrocytes were cultured for 24-, 48-, and 72-hour trials in a custom bioreactor that mimics the metabolism of synovial fluid. Chondrocytes were perfused in Dulbecco's Modified Eagle's Medium 10% fetal bovine serum and one of the following medications: 1% lidocaine, 1% lidocaine with epinephrine, 0.25% bupivacaine, 0.25% bupivacaine with epinephrine, 0.5% bupivacaine, or 0.5% bupivacaine with epinephrine. Static and perfusion cultures with growth media were used as controls. All experiments were run in duplicate. Live/dead staining was performed, and the ratio of dead:live cells was assessed by fluorescent microscopy and histomorphometry.

Results: Significantly more chondrocyte necrosis was found in all cultures with medications containing epinephrine (P < .05) at all time points. Similar necrosis rates were exhibited in 0.25% and 0.5% bupivacaine compared with controls at 24 and 48 hours. However, 0.5% bupivacaine produced significantly more cell death at 72 hours. Similar necrosis rates were exhibited with 1% lidocaine compared to controls at 24 hours.

Conclusion: In this in vitro model, 0.25% and 0.5% bupivacaine caused minimal chondrocyte necrosis when used in pain pumps for a maximum of 48 hours. All anesthetics containing epinephrine (pH <or=4) were chondrotoxic and cannot be advocated for pain pump use. The use of 0.5% bupivacaine for greater than 48 hours is not recommended.

Clinical relevance: The results of this study may help improve the safety of intra-articular pain pump use by examining the effects of local anesthetics on chondrocyte viability.