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 (< or =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).

Determination of factors influencing tissue effect of thermal chondroplasty: an ex vivo investigation.

PURPOSE: Scientific investigation of thermal chondroplasty using radiofrequency energy (RFE) is confounded by multiple factors associated with the technique. Our purpose was to determine the relative importance of the following factors on tissue effect (depth of tissue debridement plus depth of underlying cell death) of thermal chondroplasty: probe design, generator power setting, speed, force, and number of passes of the probe over treated tissue. We hypothesized the relative importance of these factors would be (from most to least important) power, passes, speed, force, and design. METHODS: Bovine patellae were treated using monopolar RFE. Sample size was based on a 2-level, half-factorial design. Low and high extremes of the factors tested were power setting (50 W v 110 W), passes (1 v 5), speed (3 mm/sec v 10 mm/sec), force (0.15 N v and 0.59 N), and probe design (electrode protrusion 25 microm v 125 microm). Samples were incubated with cell viability stain and examined using confocal laser microscopy to determine tissue effect. Data were analyzed using multiple regression. RESULTS: All factors that were tested significantly influenced tissue effect (P < .05). Power setting had the greatest effect, followed by design, speed, passes, and force. The following interactions of factors were also significant: design and force, power and passes. The optimal configuration resulting in least tissue effect was a power setting of 50 W, electrode protrusion of 25 microm, speed of 10 mm/sec, 1 pass, and 0.15 N of applied force during treatment, which resulted in a predicted tissue effect of 99 +/- 15 microm. CONCLUSIONS: The least tissue effect of thermal chondroplasty was achieved with lower power using a probe with minimal electrode protrusion while performing a rapid, single, lower force pass of the probe over treated tissue. CLINICAL RELEVANCE: Power and probe design have the greatest influence among the factors tested; selecting these parameters preoperatively could control tissue effect.