The Cancellous Bone Ablation Experimental Study With Microwave And Radiofrequency Ablation

Objective:1.To compare the heating effects between microwave andradiofrequency ablation in porcine femoral metaphysis.2. To investigate theinactivation effects、range、shape and the short term pathological changes ofimplanted microwave on swine femoral metaphysis of femur in Vivo.Methods：1. Swine femoral metaphysis ablation experiment in vitro: acomparison study of heating effects between microwave and radiofrequencyablation：Microwave and radiofrequency energy was applied for300seconds at60Watts in20porcine femoral metaphysis. Thermo sensors were placed at5mm,10mm and15mm from the electrodes, and temperatures were recorded using anadvanced temperature monitor system. The diameter, shape and temperature in theablation zone, the pathologic appearance of the ablation zone and the distributionand variation tendency of temperature were compared between microwave andradiofrequency.2. Study of microwave inactivate swine femoral metaphysisablation in vivo-Zoopery：24clean level pigs had been randomly divided into3groups and each group had been inactivated120s、240s、360s randomly andequally by microwave, sacrificed2weeks and4weeks after microwaveinactivated. Take pig femoral cancellous bone as experimental object, altogether24objects in, power was60W and frequency was2450MHz. Mophology andhistology were performed after pigs sacrificed.Results:1. Swine femoral metaphysis ablation experiment in vitro: a comparisonstudy of heating effects between microwave and radiofrequency ablation：Thelongitudinal diameters of lesions ablated with microwave and radiofrequencywere37.1±3.2mm and28.3±2.5mm respectively, and the former was significantlylonger than the later (P<0.05). The transverse diameters were21.3±1.6mm and19.8±1.4mm respectively, and the former was significantly longer than the later (P<0.05). The carbonized zone and coagulation zone could be found apparentlyfrom the microwave group, but only the coagulation zone could be found from theradiofrequency group. The radiofrequency induced more spherical lesions thanmicrowave did. The temperatures10mm from the centers of microwave andradiofrequency were126.2±1.51℃and100.2±0.70℃respectively, and theformer was significantly higher than the later (P<0.05). The temperatures10mmfrom the centers of microwave and radiofrequency were91.5±3.7℃and58.3±2.4℃respectively, and the former was significantly higher than the later (P<0.05).The microwave and radiofrequency groups could reach the steady-state at210sand255s independently. The distance from of the determination point from theheating center was shorter, and the temperature of the determination point wouldrise more faster. The heating center temperature of microwave could reach over120℃, while the heating center temperature of radiofrequency could reach a pointbelow100℃.2. Study of microwave inactivate swine femoral metaphysis ablationin vivo-Zoopery：Morphologic observation: The bone showed a reproduciblelesion. The shapes of inactivation lesions were elliptical in the vertical plane whilerotund in the horizontal plane, the inactivation ranges enlarged with the increaseof inactivation duration，the inactivation shapes tend to round with the increase ofinactivation duration. Histological observation of2weeks after inactivation: Bonetrabecular structure was normal and bone cell was complete necrosis incoagulation area, and granulation tissue formed around necrotic bone.Histological observation of4weeks after inactivation: Coagulation necrosis nidushad been absorbed,and granulation tissue invaded necrotic bone and absorbed itwith osteoclast, and new bone trabeculas had been found.Conclusion:1．Lesions induced by radiofrequency and microwave have somedifferences in shape and temperature distribution. The temperature of the heatingzone and the boundary of microwave are higher and larger than that ofradiofrequency. Compared with microwave, the radiofrequency could be controlledmore easily.2. It demonstrates that implanted microwave has inactivation effects on cancellous bone in vivo. Inactivated shape is roughly constant, bone cell is necrosisthoroughly in inactivated area. The process to repair osteonecrosis of cancellousbone after microwave inactivated is faster than it of cortical bone.