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77 Executive Briefing tissues that they contact. Radiofrequency energy excites the electro- lytic body fluids and produces an exothermic response. The extent of the exothermic response is directly related to the density of the radiofrequency current, which is greatest adjacent to the radiofre- quency electrode and cannula emitting surface and decreases rap- idly as the distance from the emitting surface increases. If all other variables are held constant, increasing the conductive surface area of the radiofrequency cannula decreases the density of the radiof- requency current. Therefore, a cannula with a larger conducting sur- face area requires greater radiofrequency energy in order to elicit an equivalent thermal response from the surrounding tissue. A can- nula with a larger conductive surface area requires that the tempera- ture-controlled radiofrequency generator increases power output to maintain a similar thermal profile, thereby creating larger lesions. The geometry of the emitting surface is another factor that contrib- utes to lesion size. Similarly shaped emitting surfaces create simi- larly shaped lesions, which are conductively cooled by surrounding tissue in a similar way. A standard radiofrequency cannula with a simple cylindrical conducting surface area creates a simple cylindri- cal shaped lesion. A complex or irregularly shaped radiofrequen- cy emitting surface will create an irregular lesion with a boundary that has a greater surface area than an emitter with a simple shape of equivalent size. This larger boundary surface area leads to in- creased conductive cooling by surrounding tissue, thereby result- ing in a larger lesion than a simple cylindrical emitting surface. In this study, Stryker investigated the Venom Cannula and Venom Electrode, a new radiofrequency cannula and electrode combina- tion in which the electrode can protrude from a side port on the exposed surface of the cannula. This design increases the surface area of the active tip, which includes both the uninsulated surface of the cannula and the protruding electrode tip. The radiofrequen- cy energy dosage with the Venom Cannula was 18% to 40% greater than the standard RF cannula for the 20-gauge size and 34% to 59% greater than the standard RF cannula for the 18-gauge size. The Venom Cannula also delivered significantly more consistent ra- diofrequency thermal dosing than the standard RF cannula. These results provided evidence that the Venom Cannula and Venom Electrode combination should create a larger lesion than a stan- dard RF cannula and electrode of the same size. To verify this theo- ry, the lesion comparison test was performed. In side-by-side lesions in ex vivo chicken breasts, the Venom Can- nula and Venom Electrode combination produced consistently larger lesions than the standard RF cannula and electrode, as shown by the cross sectional measurements and calculated vol- ume of the lesions. On average, the 20-gauge Venom Cannula created lesions of 92% greater volume than the 20-gauge stan- dard RF cannula, and the 18-gauge Venom Cannula created le- sions of 76% greater volume than the 18-gauge standard RF cannula. While it is difficult to determine the precise lesion size that the Venom Cannula will create in vivo, these results provide evidence that the Venom design will produce larger lesions than the standard cannula and electrode. Another factor that influences lesion size is the extent of electro- lytic fluid in the lesion region. Provenzano, et al. 7 showed that the injection of liquid before ablation is a simple and effective method for increasing the size of monopolar radiofrequency lesions. The additional liquid proximal to the lesion site improves both electrical and thermal conductivity. Increased electrical conductivity leads to greater radiofrequency currents and increased thermal effect on the local electrolytic fluids. Increased thermal conductivity increas- es the rate of heat dissipation to surrounding tissue, leading the closed-loop control system to automatically increase radiofrequen- cy energy levels to keep pace with the preprogrammed tempera- ture profile. To investigate how the new cannula design affects the delivery of liquid, the location of fluid propagation was compared between the Venom Cannula and the standard RF cannula. While dispensing an aliquot of dyed solution onto wetted gauze, the Venom Cannulae dispersed the dyed solution more proximal to the center of the ex- posed tip (i.e., more local to the side port), whereas the standard RF cannulae dispersed the solution in a location more distal to the exposed tip. The solution dispersion from the Venom Cannulae also provided more adequate coverage of the exposed tip than did the standard RF cannulae; the immediate dispersion of the solution did not completely encompass the exposed tip of the standard RF can- nulae. In conclusion, the Venom Cannula and Venom Electrode combi- nation created larger radiofrequency lesions than the standard RF cannula of the same gauge size and exposed tip length in ex vivo chicken breasts. In addition, when a fluid was dispensed down the Venom Cannula, the immediate propagation of the fluid was more local to the exposed tip than it was with a standard RF cannula, suggesting that the Venom Cannula may provide more efficient delivery of anesthesia to a targeted lesion zone, which may lead to greater procedural efficiency. n Stryker part numbers used: 20-gauge Venom Cannula, part no. 0406-660-125; 20-gauge standard RF cannula, part no. 0406-630-125; 18-gauge Venom Cannula, part no. 0406860-125; 18-gauge standard RF cannula, part no. 0406840-125; and MultiGen Radiofrequency Generator, part no. 0406-900-000. References 1 Effect of the Stryker Venom ® Cannula and Venom ® Electrode Combina- tion on Lesion Size and Anesthesia Delivery During Radiofrequency Ablation. Stryker Instruments, 4100 East Milham Avenue, Kalamazoo, Michigan 49001. 2 Fenton DS, Czervionke LF. Chapter 3 Facet Denervation. In: Image-Guided Spine Intervention 1st Ed. Saunders; 2002:51-71. 3 Markman JD, Philip A. Interventional approaches to pain management. Anes- thesiol Clin. 2007;25:883–898. 4 Nath S, Nath CA, Pettersson K. Percutaneous lumbar zygapophysial (facet) joint neurotomy using radiofrequency current in the management of chronic low back pain. A randomized double-blind trial. Spine. 2008;33(12):1291-1297; Discussion 1298. 5 Stryker Interventional Spine. Radiofrequency Ablation Procedure Overview Web Site. http://strykerivs.com/procedures/radiofrequencyablation/procedure-over- view. Accessed November 12, 2012. 6 Cohen SP, Rathmell JP. Tackling the technical challenges that hinder the suc- cess of facet joint radiofrequency treatment for spinal pain. Reg Anesth Pain Med. 2010;35(4):327-328. 7 Provenzano DA, Lassila HC, Somers D. The effect of fluid injection on lesion size during radiofrequency treatment. Reg Anesth Pain Med. 2010;35(4):338-342. 8 Mulier S, Jiang Y, Wang C, et al. Bipolar radiofrequency ablation with four elec- trodes: Ex vivo liver experiments and finite element method analysis. Influence of interelectrode distance on coagulation size and geometry. Int J Hyperthermia. 2012;28(7):686-697. 1000-025-552 Rev none Stryker is one of the world's leading medical technology companies and, together with our customers, we are driven to make healthcare better. The Company offers a diverse array of innovative products and services in Orthopaedics, Medical and Surgical, and Neurotechnolo- gy and Spine that help improve patient and hospital outcomes. Stryker is active in over 100 countries around the world.