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

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.