Thermometric determination of cartilage matrix temperatures during thermal chondroplasty: comparison of bipolar and monopolar radiofrequency devices

Purpose: To compare cartilage matrix temperatures between monopolar radiofrequency energy (mRFE) and bipolar RFE (bRFE) at 3 depths under the articular surface during thermal chondroplasty. We hypothesized that cartilage temperatures would be higher at all cartilage depths for the bRFE device than for the mRFE device. Type of Study: Randomized trial using bovine cartilage. Methods: Sixty osteochondral sections from the femoropatellar joint of 15 adult cattle were used for this study. Using a custom jig, fluoroptic thermometry probes were placed at one of the following depths under the articular surface: 200 Am, 500 mum, or 2,000 mum, RF treatment was performed either with fluid flow (F) (120 mL/min) or without fluid flow (NF) (n = 5/depth/RFE device/flow; total specimens, 60). Irrigation fluid temperature was room temperature (22degreesC). Thermometry data were acquired at 4 Hz for 5 seconds with the RF probe off, for 20 seconds with the RF probe on, and then for 15 seconds with the RF probe off. During RF treatment, a 0.79-cm(2) area (1.0-cm diameter) of the articular surface centered over the thermometry probe was treated in a paintbrush manner in noncontact (bRFE) or light contact (mRFE). L Results: Thermal chondroplasty with bRFE resulted in higher cartilage matrix temperatures compared with mRFE for all depths and regardless of fluid flow. Bipolar RFE resulted in temperatures of 95degreesC to 100degreesC at 200 Am and 500 Am under the surface, with temperatures of 75degreesC to 78degreesC at 2,000 Am. Fluid flow during bRFE application had no effect at 200 mum. Monopolar RFE resulted in temperatures of 61degreesC to 68degreesC at 200 mum, 54degreesC to 70degreesC at 500 mum under the surface, and 28degreesC to 30degreesC at 2,000 Am below the surface. A significant effect of fluid flow during mRFE application occurred at 200 mum (NF, 61degreesC; F, 63degreesC) and 500 mum (NF, 53degreesC; F, 68degreesC). Conclusions: In this study, we found significant differences between bRFE and a temperature-controlled mRFE device with regard to depth of thermal heating of cartilage in vitro. Bipolar RFE resulted in matrix temperatures high enough (>70degreesC to kill cells as deep as 2,000 mum under the articular surface. Fluid flow during thermal chondroplasty had the effect of significantly increasing cartilage matrix temperatures at 200 and 500 mum with the mRFE device. During thermal chondroplasty, bRFE creates greater matrix temperature elevations at equivalent depths and treatment duration than does mRFE. Excessive temperatures generated deep within the cartilage matrix could cause full-thickness chondrocyte death, in vivo.