An Ex Vivo Thermal Chondroplasty Model: The Association of a Char-Like Layer and Underlying Cell Death

Purpose: The purpose of this study was to evaluate the relation between the char-like layer observed during radiofrequency energy (RFE) treatment of cartilage and the depth of underlying cell death. Methods: Healthy adult bovine patellae were treated with a monopolar RFE probe ex vivo at generator settings of 20, 30, 40, 50, 60, 80, and 110 in cut mode. The presence or absence of a char-like layer and visual electrical discharge was noted. Treated tissue was incubated with cell viability stain, and the depth of cell death and matrix debridement was measured from confocal laser microscopy images. Results: At generator settings of 60 and above, a char-like layer, electrical discharge, and matrix debridement were consistently observed, and the depth of cell death was significantly less (P < .05) than when these features were not observed (≤30). Paradoxically, the least depth of cell death did not occur at the lowest generator setting in cut mode. It occurred at a generator setting of 60. An increase in impedance of the system and a decrease in current were also associated with reduced cell death. Conclusions: In this controlled ex vivo study formation of a char-like layer, visual electrical discharge, increased impedance, and reduced current were associated with less depth of cell death when cartilage was treated with monopolar RFE. Clinical Relevance: This study suggests that a char-like layer and electrical discharge during RFE treatment of cartilage may be advantageous because, potentially, these features are associated with less depth of cell death (safety) and greater matrix debridement (efficacy).