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Monopolar Radiofrequency Use in Deep Gluteal Space Endoscopy: Sciatic Nerve Safety and Fluid Temperature
Monopolar Radiofrequency Use in Deep Gluteal Space Endoscopy: Sciatic Nerve Safety and Fluid Temperature Hal David Martin, D.O., Ian James Palmer, Ph.D., and Munif Hatem, M.D.
Purpose: The purpose of this study was to evaluate the temperature at the sciatic nerve when using a monopolar radiofrequency (RF) probe to control bleeding in deep gluteal space endoscopy, as well as assess the fluid temperature profile. Methods: Ten hips in 5 fresh-frozen human cadaveric specimens from the abdomen to the toes were used for this experiment. Temperatures were measured at the sciatic nerve after 2, 5, and 10 seconds of continuous RF probe activation over an adjacent vessel, a branch of the inferior gluteal artery. Fluid temperatures were then measured at different distances from the probe (3, 5, and 10 mm) after 2, 5, and 10 seconds of continuous probe activation. All tests were performed with irrigation fluid flow at 60 mm Hg allowing outflow. Results: After 2, 5, or 10 seconds of activation over the crossing branch of the inferior gluteal artery, the mean temperature increased by less than 1 C on the surface and in the perineurium of the sciatic nerve. Considering the fluid temperature profile in the deep gluteal space, the distance and duration of activation influenced temperature (P < .05). Continuous delivery of RF energy for 10 seconds caused fluid temperature increases of 1.2 C, 2 C, and 3.1 C on average at 10 mm, 5 mm, and 3 mm of distance, respectively. Conclusions: This study found the tested monopolar RF device to be safe during use in vessels around the sciatic nerve after 2, 5, and 10 seconds of continuous activation. The maximum fluid temperature (28 C) after 10 seconds of activation at 3 mm of distance is lower than the minimal reported temperature necessary to cause nerve changes (40 C to 45 C). Clinical Relevance: Monopolar RF seems to be safe to the neural structures when used at more than 3 mm of distance and with less than 10 seconds of continuous activation in deep gluteal space endoscopy with fluid inflow and outflow.
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ndoscopic procedures for deep gluteal space disorders are increasingly being performed as the understanding of posterior hip pain evolves. The most frequent indication for deep gluteal space endoscopy is decompression of the sciatic nerve.1,2 This procedure often requires the use of radiofrequency (RF) energy for dissection or bleeding control. It is known that RF devices can affect temperature during arthroscopic surgeries.3,4 However, there have been no data regarding sciatic nerve safety and the fluid temperature profile during the use of RF probes in endoscopic procedures in the deep gluteal space.
From the Baylor University Medical Center (H.D.M., I.J.P.), Dallas, Texas, U.S.A.; and Hospital de Clínicas da Universidade Federal do Paraná (M.H.), Curitiba, Brazil. The authors report the following potential conflict of interest or source of funding: H.D.M. receives support from Pivot and Smith & Nephew. Received April 23, 2013; accepted August 28, 2013. Address correspondence to Hal David Martin, D.O., Baylor University Medical Center, 411 N Washington Ave, Ste 7300, Dallas, TX 75246, U.S.A. E-mail: [email protected] Ó 2014 by the Arthroscopy Association of North America 0749-8063/13267/$36.00 http://dx.doi.org/10.1016/j.arthro.2013.08.034
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RF is an electromagnetic wave with a frequency between audio and infrared, ranging from 104 to 3 102.5 Alternating currents with frequencies higher than 104 Hz are known for not causing a neuromuscular response.5 Therefore the risk of nerve damage using RF energy is triggered by heat. Animal studies have already reported the thermic effects of RF energy on nerve function and histology. Different authors have described a reversible sciatic nerve block when this nerve was exposed to temperatures from 40 C to 45 C for 12 to 58 minutes.6-8 Another animal experiment reported the effect in the nerve after 45 seconds of heating: at 50 C, there was no nerve fiber damage; at 55 C, approximately half of the cut surface of the nerve was affected; and at 60 C, nearly the total cut surface of the nerve was injured.9 Nevertheless, irrigation fluid has been reported to protect nerves against thermal injury from instruments of electricity-generated heat.10 Good et al.3 and Zoric et al.4 reported that irrigation is the most important factor to influence temperature during RF use in shoulder arthroscopy, with higher flow conditions protecting against temperature elevation. The superficial crossing branches of the inferior gluteal vessels (CBIGVs) are posterior to the sciatic nerve and distal to the piriformis muscle (Fig 1). To
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Fig 1. CBIGVs posterior to the sciatic nerve (SN).
access the piriformis muscle in endoscopic sciatic nerve decompression,1,2 these vessels should often be coagulated or ligated when larger. Other vascular structures are occasionally also coagulated during deep gluteal space procedures.2 The purpose of this study was to evaluate the temperature at the sciatic nerve when using a monopolar RF probe to control bleeding during deep gluteal space endoscopy, as well as assess the fluid temperature profile. The hypothesis was that monopolar RF use in the deep gluteal space is safe from dangerous thermal increases with a shorter activation time and greater distance.
Methods Ten hips in 5 fresh-frozen human cadaveric specimens from the abdomen to the toes, with all soft tissues maintained, were used for this experiment. The pelvis and lower limbs were preserved to maintain sciatic nerve tension and the relation between the sciatic nerve and the CBIGVs. The specimens were thawed to room temperature before the experiment. The cadaveric specimens were positioned on a traction table with 30 of contralateral tilt. The deep gluteal space was accessed through the anterolateral portal, the posterolateral portal, and an auxiliary posterolateral portal (3 cm posterior and 3 cm superior to the greater trochanter).2 Arthroscopic cannulas and a standard 70 arthroscope were used. Saline solution at room temperature (19 C to 21 C) was used with an inflow pressure of 60 mm Hg, which is the pressure used during the standard technique for deep gluteal space procedures2 and was the pressure used by Zoric et al.4 in a previous study. Outflow through the cannulas was noted in each specimen during the tests, although it was not measured. The identification steps were as follows2: (1) peritrochanteric space inspection and bursectomy, (2) visualization of the quadratus femoris muscle and sciatic nerve, (3) identification of the obturator internus
Fig 2. The distance between the CBIGVs and the sciatic nerve (SN) was determined with an arthroscopic ruler at the middle of the vessel. More than 1 view was obtained by turning the 70 arthroscope before the final measurement.
muscle and tendon, and (4) identification of the CBIGVs posterior to the sciatic nerve and distal to the piriformis muscle. After CBIGVs identification with the arthroscope positioned in the anterolateral portal, 2 monopolar RF devices (TAC-S probes; Smith & Nephew Endoscopy, Andover, MA) were placed in the deep gluteal space. The energy probe (used to deliver RF energy) was introduced first through the posterolateral portal, under a programmed temperature of 75 C. A grounding pad was secured at the abdomen and connected to the electrothermal system of the energy probe. The second control probe (used to obtain the temperature profile) was attached to a different electrothermal system, set up only for “temperature” control without delivering RF energy. This control probe entered the deep gluteal space through the auxiliary posterolateral portal. Temperature was assessed before and at the end of each period of energy probe activation. Temperature tests were performed in 2 different phases. Tests performed first were related to the CBIGVs and sciatic nerve. Subsequent tests were performed to assess the fluid temperature profile related to activation time and distance within the deep gluteal space. Tests Related to CBIGVs and Sciatic Nerve First, the distance between the CBIGVs and the sciatic nerve was determined with an arthroscopic ruler (Fig 2). The measurement was taken at the middle of the vessel. Next, the energy probe touched the CBIGVs and was continuously activated for 2, 5, and 10 seconds while the control probe was used for temperature assessment on the surface of the sciatic nerve. After that, the energy probe was activated in the same manner with the control
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H. D. MARTIN ET AL. Table 1. Mean Temperature Assessed at Sciatic Nerve After Different Times of Continuous Probe Activation over CBIGVs Temperature in Relation to Sciatic Nerve ( C) Activation Time 0s 2s 5s 10 s
On Surface 19.9 (19-21) 20.5 (19-22) 20.7 (19-24) 20.8 (20-22)
In Perineurium 18.4 (17-20) 18.5 (17-20) 18.6 (17-21) 19.1 (17-22)
NOTE. Data are presented as mean (range) for the 10 specimens.
Pearson correlation coefficient was used to determine any relation between distance and temperature. All data are reported as mean standard deviation.
Results Fig 3. Endoscopic view of RF control probe (left) and energy probe (right). The edge of the energy probe was aligned to the markings placed at 3, 5, and 10 mm from the tip of the control probe.
probe placed inside the sciatic nerve to measure the temperature in the perineurium at the level of the vessel. Tests to Assess Fluid Temperature Profile in Deep Gluteal Space We performed tests to determine the fluid temperature profile more distally without touching any anatomic structure with the probe tip. The energy probe was activated at 3 different distances (3, 5, and 10 mm) from the tip of the control probe. The distances were marked on the control probe, and the edge of the energy probe was aligned at the markings (Fig 3). The control probe and energy probe were confirmed to be on the same plane by touching the energy probe (without activation) to the surface of the control probe. Furthermore, the 70 arthroscope was turned to obtain a different view. After confirmation of probe alignment, both were maintained apart during activation. Three distinct continuous activation intervals (2, 5, and 10 seconds) were used at each distance. The following technical instructions were followed throughout the tests. During activation, no contact between probes occurred to avoid an electric current between the 2 electrothermal systems. The read temperature in each condition was recorded on a graph, and the fluid temperature was allowed to return to baseline after every activation period. For each test, the arthroscope was focused and centered on the RF probe at a distance of approximately 8 mm to minimize any variance.4 Statistical Analyses Repeated-measures analyses of variance were performed for each testing situation. Paired t tests were performed post hoc for determination of temperature differences. The
The mean distance between the sciatic nerve and the CBIGVs was 8 4.1 mm (range, 4 to 14 mm). The mean width of the CBIGVs was 2 mm; therefore the anterior edge of the vessel was an average of 7 mm from the sciatic nerve. The baseline temperature was 19.9 C at the surface of the sciatic nerve (Table 1). With continuous delivery of energy on the CBIGVs, the mean temperatures were 20.5 C (2 seconds), 20.7 C (5 seconds), and 20.8 C (10 seconds) (P > .05). Inside the perineurium of the sciatic nerve (Table 1), the baseline temperature was 18.4 C. With continuous delivery of energy at the level of the CBIGVs, the mean temperatures were 18.5 C (2 seconds), 18.6 C (5 seconds), and 19.1 C (10 seconds) (P < .05). Post hoc t tests found that values after 10 seconds of continuous activation were significantly greater than baseline values (P < .05). No significant correlations were found between the distance of the CBIGVs and temperature. For the distance and activation time parameters (Table 2), the baseline temperature at the level of the sciatic nerve was 20.6 C. With the energy probe at a distance of 10 mm, significant temperature changes were found (P < .01). The temperature increased to 21.0 C with 2 seconds of activation (P < .05), to 21.8 C with 5 seconds of activation (P < .01), and to 21.8 C with 10 seconds of activation (P < .01). With the energy probe at a distance of 5 mm, significant temperature changes were found (P < .01). The temperature increased to 21.6 C with 2 seconds of activation (P < .01), to 22.3 C Table 2. Fluid Temperature Assessed at Sciatic Nerve at Different Intervals of Distance and Duration Fluid Temperature ( C) Activation Time 0s 2s 5s 10 s
10 mm From Sciatic Nerve 20.6 (20-21) 21.0 (20-22) 21.8 (21-24) 21.8 (21-23)
5 mm From Sciatic Nerve 20.6 (20-21) 21.6 (20-23) 22.3 (21-25) 22.6 (21-24)
3 mm From Sciatic Nerve 20.6 (20-21) 21.8 (21-23) 22.8 (21-25) 23.7 (22-28)
NOTE. Data are presented as mean (range) for the 10 specimens.
RADIOFREQUENCY AND DEEP GLUTEAL SPACE
with 5 seconds of activation (P < .01), and to 22.6 C with 10 seconds of activation (P < .01). With the energy probe at a distance of 3 mm, significant temperature changes were found (P < .01). The temperature increased to 21.8 C with 2 seconds of activation (P < .01), to 22.8 C with 5 seconds of activation (P < .01), and to 23.7 C with 10 seconds of activation (P < .01).
Discussion Our results showed that the temperature in the sciatic nerve was not significantly increased after 2, 5, and 10 seconds of continuous activation of the TAC-S monopolar RF device on adjacent vessels. The tissue in contact with the RF probe itself may absorb most of the energy from the probe, thereby preventing an increase in fluid temperature. Obrzut et al.11 tested the temperature increase when applying the TAC-S probe in sheep capsular tissue prepared at 37 C. They found that the temperature at 1.5 mm was always less than 45 C. The distance of the CBIGVs to the sciatic nerve in our study ranged from 4 to 14 mm and showed no correlation with temperature at 2, 5, or 10 seconds of activation. After activation of the RF probe without touching any tissue, the maximum temperature at 3 mm with 10 seconds of continuous activation was 8 C (20 C to 28 C). This temperature elevation appears to be safe to the sciatic nerve. Experiments in animals have shown nerve changes with higher temperatures and longer periods of heating exposure. Wondergem et al.8 performed heat treatment of rat sciatic nerves and reported functional loss occurring after 58, 32, and 12 minutes of heating at 43 C, 44 C, and 45 C, respectively. Complete recovery occurred in all rats after 4 weeks. Hoogeveen et al.7 observed that hyperthermic injury for 30 minutes at 45 C slowly affected both motor and sensory function, taking about 7 hours until maximum dysfunction occurred. Motor function recovered completely within 9 days. Monafo and Eliasson12 related an apparently irreversible conduction block in 67% of tibial nerves after exposing rat sciatic nerves to 47 C for 30 seconds. The thermoprotective effects of irrigation to neural structures have been suggested by Donzelli et al.10 after experiments with bipolar cautery in sciatic nerves of rats. Irrigation fluid reduced the temperature response during the 15 seconds after the stimulation with bipolar cautery. Irrigation also reduced the degree of paresis and neuropathological changes when compared with a non-irrigation group. Thermic nerve injury using RF energy for capsular shrinkage has been a concern in shoulder arthroscopy.11,13-16 Zoric et al.4 studied the temperature profile associated with a bipolar RF ablation device within the glenohumeral space. The temperature profile was not apparently influenced by the voltage, and the flow rate was considered the most significant predictor of intra-
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articular temperatures. In a scenario of no flow (both the RF suction and the inflow were off), temperatures higher than 50 C were found in 12% of cases after 5 seconds of activation. In conditions of fluid inflow and no suction, the authors measured a mean temperature of 25 C at 3 mm after 10 seconds of activation. In our study the mean temperature was 23.7 C (range, 22 C to 28 C) at the same distance and time of activation. This difference may be related to the maintenance of fluid outflow in our study, even though we did not use suction. When inflow was on, Zoric et al. also observed a mean temperature lower than 30 from 0 to 120 seconds of continuous activation. We used continuous inflow and outflow of saline solution during all tests to reproduce the surgical technique used in deep gluteal space procedures.2 Whereas the maximum tested time of activation was 10 seconds in our study, other authors tested the temperature up to 120 seconds.3,4 We wanted to reproduce a practical scenario, in which less than 5 seconds of continuous activation is necessary to coagulate small vessels in the deep gluteal space in our experience. Our standard approach to vessel cauterization is one 3-second interval with continuous irrigation, followeddif necessarydby a second 3-second interval maintaining continuous irrigation. In an in vivo scenario, we noted that 3 seconds of activation allows a good contraction of the collagen of the vessel to control bleeding. For vessels larger than 2 mm, a ligature is used rather than a longer activation time. Fluid inflow comes through the arthroscope during arthroscopy and may be different depending on the cannula and arthroscope design.4 Although we did not observe a difference between multi-fenestrated and non-fenestrated arthroscopic cannulas in a preliminary study, we used a 70 arthroscope delivering unidirectional flow during all tests. With this type of arthroscope, the center of view does not match the inflow direction, and most of the inflow is not directed to the RF probe. Arthroscopes of 30 and distinct arthroscopic cannulas may have a different effect on the fluid temperature when activating RF devices. The RF devices can be monopolar or bipolar. The monopolar devices have a single active electrode, and the current is dissipated by a grounding pad. The bipolar devices have 2 active electrodes, the first for delivering the current and the second for returning the current.5 We used monopolar TAC-S probes in this experiment because the adjustable bending tip allowed more precise positioning at the CBIGVs and sciatic nerve. We could not satisfactorily access the points of interest using larger and/or unbendable bipolar RF devices. Considering the temperature assessment, we also could not position the regular thermocouples at the CBIGVs and sciatic nerve. TAC-S probes were used for temperature measurement, considering that a thermocouple is present in the tip of these devices. Moreover,
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equivalent temperature measurements between the TAC-S and regular thermocouple probes were observed in a preliminary study. Lu et al.17 have already described differences in tissue temperature effects depending on the type of RF device. The TAC-S probe is a temperature-controlled monopolar device, with the power of delivered RF energy determined by the temperature measured at its tip by a thermocouple. Although the continuous activation of the RF monopolar probe for 2, 5, and 10 seconds over vessels adjacent to the sciatic nerve was safe to this nerve in this study, the results cannot be extrapolated to other RF devices. Limitations This study presents a number of limitations to be considered when interpreting the results. First, histologic and electrophysiological sciatic nerve changes provoked by RF energy were not evaluated in this in vitro study. However, studies in animals have already related functional and histopathological changes according to the amount of heating.6-9,12 A second limitation relates to the reliability of the distance measurement under an endoscopic view. We used a 70 arthroscope with frequent changes in the direction of view to increase the accuracy. In addition, before each set of activation at 3, 5 and 10 mm of distance from the control probe tip, the energy probe tip touched the marks on the control probe to confirm that they were on the same plane. A third limitation applies to the fact that the distance between the arthroscope and the energy probe was not objectively controlled using a view from another arthroscope, and this factor may influence the irrigation from the arthroscope to the TAC-S. Lastly, considering that cadaveric tissue temperature is lower than in vivo temperature, colder CBIGVs could minimize the temperature increase in the sciatic nerve. Nevertheless, the TAC-S is a temperature-controlled device, and cooler tissue increases the RF generator output.
Conclusions This study found the tested monopolar RF device to be safe during use in vessels around the sciatic nerve after 2, 5, and 10 seconds of continuous activation. The maximum fluid temperature (28 C) after 10 seconds of activation at 3 mm of distance is lower than the minimal reported temperature necessary to cause nerve changes (40 C to 45 C).
References 1. Martin HD, Hatem M, Palmer IJ. Endoscopic sciatic nerve decompression: Operative technique. Oper Tech Sports Med 2012;20:325-332.
2. Martin HD, Shears SA, Johnson JC, Smathers AM, Palmer IJ. The endoscopic treatment of sciatic nerve entrapment/deep gluteal syndrome. Arthroscopy 2011;27:172-181. 3. Good CR, Shindle MK, Griffith MH, Wanich T, Warren RF. Effect of radiofrequency energy on glenohumeral fluid temperature during shoulder arthroscopy. J Bone Joint Surg Am 2009;91:429-434. 4. Zoric BB, Horn N, Braun S, Millett PJ. Factors influencing intra-articular fluid temperature profiles with radiofrequency ablation. J Bone Joint Surg Am 2009;91: 2448-2454. 5. Ni Y, Mulier S, Miao Y, Michel L, Marchal G. A review of the general aspects of radiofrequency ablation. Abdom Imaging 2005;30:381-400. 6. Brodkey J, Miyazaki Y, Ervin F, Mark V. Reversible heat lesions with radiofrequency current. A method of stereotactic localization. J Neurosurg 1964;21:49-53. 7. Hoogeveen JF, Troost D, Wondergem J, van der Kracht AH, Haveman J. Hyperthermic injury versus crush injury in the rat sciatic nerve: A comparative functional, histopathological and morphometrical study. J Neurol Sci 1992;108:55-64. 8. Wondergem J, Haveman J, Rusman V, Sminia P, Van Dijk JD. Effects of local hyperthermia on the motor function of the rat sciatic nerve. Int J Radiat Biol Relat Stud Phys Chem Med 1988;53:429-438. 9. Fröhling MA, Schlote W, Wolburg-Buchholz K. Nonselective nerve fibre damage in peripheral nerves after experimental thermocoagulation. Acta Neurochir (Wien) 1998;140:1297-1302. 10. Donzelli J, Leonetti JP, Wurster RD, Lee JM, Young MR. Neuroprotection due to irrigation during bipolar cautery. Arch Otolaryngol Head Neck Surg 2000;126:149-153. 11. Obrzut SL, Hecht P, Hayashi K, Fanton GS, Thabit G, Markel MD. The effect of radiofrequency energy on the length and temperature properties of the glenohumeral joint capsule. Arthroscopy 1998;14:395-400. 12. Monafo WW, Eliasson SG. Sciatic nerve function following hindlimb thermal injury. J Surg Res 1987;43:344-350. 13. Greis PE, Burks RT, Schickendantz MS, Sandmeier R. Axillary nerve injury after thermal capsular shrinkage of the shoulder. J Shoulder Elbow Surg 2001;10:231-235. 14. Gryler EC, Greis PE, Burks RT, West J. Axillary nerve temperatures during radiofrequency capsulorrhaphy of the shoulder. Arthroscopy 2001;17:567-572. 15. McCarty EC, Warren RF, Deng X-H, Deng X-H, Craig EV, Potter H. Temperature along the axillary nerve during radiofrequency-induced thermal capsular shrinkage. Am J Sports Med 2004;32:909-914. 16. Wong KL, Williams GR. Complications of thermal capsulorrhaphy of the shoulder. J Bone Joint Surg Am 2001;83(suppl):151-155. 17. Lu Y, Edwards RB, Cole BJ, Markel MD. Thermal chondroplasty with radiofrequency energy. An in vitro comparison of bipolar and monopolar radiofrequency devices. Am J Sports Med 2001;29:42-49.
Purpose: The purpose of this study was to evaluate the temperature at the sciatic nerve when using a monopolar radiofrequency (RF) probe to control bleeding in deep gluteal space endoscopy, as well as assess the fluid temperature profile. Methods: Ten hips in 5 fresh-frozen human cadaveric specimens from the abdomen to the toes were used for this experiment. Temperatures were measured at the sciatic nerve after 2, 5, and 10 seconds of continuous RF probe activation over an adjacent vessel, a branch of the inferior gluteal artery. Fluid temperatures were then measured at different distances from the probe (3, 5, and 10 mm) after 2, 5, and 10 seconds of continuous probe activation. All tests were performed with irrigation fluid flow at 60 mm Hg allowing outflow. Results: After 2, 5, or 10 seconds of activation over the crossing branch of the inferior gluteal artery, the mean temperature increased by less than 1 C on the surface and in the perineurium of the sciatic nerve. Considering the fluid temperature profile in the deep gluteal space, the distance and duration of activation influenced temperature (P < .05). Continuous delivery of RF energy for 10 seconds caused fluid temperature increases of 1.2 C, 2 C, and 3.1 C on average at 10 mm, 5 mm, and 3 mm of distance, respectively. Conclusions: This study found the tested monopolar RF device to be safe during use in vessels around the sciatic nerve after 2, 5, and 10 seconds of continuous activation. The maximum fluid temperature (28 C) after 10 seconds of activation at 3 mm of distance is lower than the minimal reported temperature necessary to cause nerve changes (40 C to 45 C). Clinical Relevance: Monopolar RF seems to be safe to the neural structures when used at more than 3 mm of distance and with less than 10 seconds of continuous activation in deep gluteal space endoscopy with fluid inflow and outflow.
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ndoscopic procedures for deep gluteal space disorders are increasingly being performed as the understanding of posterior hip pain evolves. The most frequent indication for deep gluteal space endoscopy is decompression of the sciatic nerve.1,2 This procedure often requires the use of radiofrequency (RF) energy for dissection or bleeding control. It is known that RF devices can affect temperature during arthroscopic surgeries.3,4 However, there have been no data regarding sciatic nerve safety and the fluid temperature profile during the use of RF probes in endoscopic procedures in the deep gluteal space.
From the Baylor University Medical Center (H.D.M., I.J.P.), Dallas, Texas, U.S.A.; and Hospital de Clínicas da Universidade Federal do Paraná (M.H.), Curitiba, Brazil. The authors report the following potential conflict of interest or source of funding: H.D.M. receives support from Pivot and Smith & Nephew. Received April 23, 2013; accepted August 28, 2013. Address correspondence to Hal David Martin, D.O., Baylor University Medical Center, 411 N Washington Ave, Ste 7300, Dallas, TX 75246, U.S.A. E-mail: [email protected] Ó 2014 by the Arthroscopy Association of North America 0749-8063/13267/$36.00 http://dx.doi.org/10.1016/j.arthro.2013.08.034
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RF is an electromagnetic wave with a frequency between audio and infrared, ranging from 104 to 3 102.5 Alternating currents with frequencies higher than 104 Hz are known for not causing a neuromuscular response.5 Therefore the risk of nerve damage using RF energy is triggered by heat. Animal studies have already reported the thermic effects of RF energy on nerve function and histology. Different authors have described a reversible sciatic nerve block when this nerve was exposed to temperatures from 40 C to 45 C for 12 to 58 minutes.6-8 Another animal experiment reported the effect in the nerve after 45 seconds of heating: at 50 C, there was no nerve fiber damage; at 55 C, approximately half of the cut surface of the nerve was affected; and at 60 C, nearly the total cut surface of the nerve was injured.9 Nevertheless, irrigation fluid has been reported to protect nerves against thermal injury from instruments of electricity-generated heat.10 Good et al.3 and Zoric et al.4 reported that irrigation is the most important factor to influence temperature during RF use in shoulder arthroscopy, with higher flow conditions protecting against temperature elevation. The superficial crossing branches of the inferior gluteal vessels (CBIGVs) are posterior to the sciatic nerve and distal to the piriformis muscle (Fig 1). To
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 30, No 1 (January), 2014: pp 60-64
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Fig 1. CBIGVs posterior to the sciatic nerve (SN).
access the piriformis muscle in endoscopic sciatic nerve decompression,1,2 these vessels should often be coagulated or ligated when larger. Other vascular structures are occasionally also coagulated during deep gluteal space procedures.2 The purpose of this study was to evaluate the temperature at the sciatic nerve when using a monopolar RF probe to control bleeding during deep gluteal space endoscopy, as well as assess the fluid temperature profile. The hypothesis was that monopolar RF use in the deep gluteal space is safe from dangerous thermal increases with a shorter activation time and greater distance.
Methods Ten hips in 5 fresh-frozen human cadaveric specimens from the abdomen to the toes, with all soft tissues maintained, were used for this experiment. The pelvis and lower limbs were preserved to maintain sciatic nerve tension and the relation between the sciatic nerve and the CBIGVs. The specimens were thawed to room temperature before the experiment. The cadaveric specimens were positioned on a traction table with 30 of contralateral tilt. The deep gluteal space was accessed through the anterolateral portal, the posterolateral portal, and an auxiliary posterolateral portal (3 cm posterior and 3 cm superior to the greater trochanter).2 Arthroscopic cannulas and a standard 70 arthroscope were used. Saline solution at room temperature (19 C to 21 C) was used with an inflow pressure of 60 mm Hg, which is the pressure used during the standard technique for deep gluteal space procedures2 and was the pressure used by Zoric et al.4 in a previous study. Outflow through the cannulas was noted in each specimen during the tests, although it was not measured. The identification steps were as follows2: (1) peritrochanteric space inspection and bursectomy, (2) visualization of the quadratus femoris muscle and sciatic nerve, (3) identification of the obturator internus
Fig 2. The distance between the CBIGVs and the sciatic nerve (SN) was determined with an arthroscopic ruler at the middle of the vessel. More than 1 view was obtained by turning the 70 arthroscope before the final measurement.
muscle and tendon, and (4) identification of the CBIGVs posterior to the sciatic nerve and distal to the piriformis muscle. After CBIGVs identification with the arthroscope positioned in the anterolateral portal, 2 monopolar RF devices (TAC-S probes; Smith & Nephew Endoscopy, Andover, MA) were placed in the deep gluteal space. The energy probe (used to deliver RF energy) was introduced first through the posterolateral portal, under a programmed temperature of 75 C. A grounding pad was secured at the abdomen and connected to the electrothermal system of the energy probe. The second control probe (used to obtain the temperature profile) was attached to a different electrothermal system, set up only for “temperature” control without delivering RF energy. This control probe entered the deep gluteal space through the auxiliary posterolateral portal. Temperature was assessed before and at the end of each period of energy probe activation. Temperature tests were performed in 2 different phases. Tests performed first were related to the CBIGVs and sciatic nerve. Subsequent tests were performed to assess the fluid temperature profile related to activation time and distance within the deep gluteal space. Tests Related to CBIGVs and Sciatic Nerve First, the distance between the CBIGVs and the sciatic nerve was determined with an arthroscopic ruler (Fig 2). The measurement was taken at the middle of the vessel. Next, the energy probe touched the CBIGVs and was continuously activated for 2, 5, and 10 seconds while the control probe was used for temperature assessment on the surface of the sciatic nerve. After that, the energy probe was activated in the same manner with the control
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H. D. MARTIN ET AL. Table 1. Mean Temperature Assessed at Sciatic Nerve After Different Times of Continuous Probe Activation over CBIGVs Temperature in Relation to Sciatic Nerve ( C) Activation Time 0s 2s 5s 10 s
On Surface 19.9 (19-21) 20.5 (19-22) 20.7 (19-24) 20.8 (20-22)
In Perineurium 18.4 (17-20) 18.5 (17-20) 18.6 (17-21) 19.1 (17-22)
NOTE. Data are presented as mean (range) for the 10 specimens.
Pearson correlation coefficient was used to determine any relation between distance and temperature. All data are reported as mean standard deviation.
Results Fig 3. Endoscopic view of RF control probe (left) and energy probe (right). The edge of the energy probe was aligned to the markings placed at 3, 5, and 10 mm from the tip of the control probe.
probe placed inside the sciatic nerve to measure the temperature in the perineurium at the level of the vessel. Tests to Assess Fluid Temperature Profile in Deep Gluteal Space We performed tests to determine the fluid temperature profile more distally without touching any anatomic structure with the probe tip. The energy probe was activated at 3 different distances (3, 5, and 10 mm) from the tip of the control probe. The distances were marked on the control probe, and the edge of the energy probe was aligned at the markings (Fig 3). The control probe and energy probe were confirmed to be on the same plane by touching the energy probe (without activation) to the surface of the control probe. Furthermore, the 70 arthroscope was turned to obtain a different view. After confirmation of probe alignment, both were maintained apart during activation. Three distinct continuous activation intervals (2, 5, and 10 seconds) were used at each distance. The following technical instructions were followed throughout the tests. During activation, no contact between probes occurred to avoid an electric current between the 2 electrothermal systems. The read temperature in each condition was recorded on a graph, and the fluid temperature was allowed to return to baseline after every activation period. For each test, the arthroscope was focused and centered on the RF probe at a distance of approximately 8 mm to minimize any variance.4 Statistical Analyses Repeated-measures analyses of variance were performed for each testing situation. Paired t tests were performed post hoc for determination of temperature differences. The
The mean distance between the sciatic nerve and the CBIGVs was 8 4.1 mm (range, 4 to 14 mm). The mean width of the CBIGVs was 2 mm; therefore the anterior edge of the vessel was an average of 7 mm from the sciatic nerve. The baseline temperature was 19.9 C at the surface of the sciatic nerve (Table 1). With continuous delivery of energy on the CBIGVs, the mean temperatures were 20.5 C (2 seconds), 20.7 C (5 seconds), and 20.8 C (10 seconds) (P > .05). Inside the perineurium of the sciatic nerve (Table 1), the baseline temperature was 18.4 C. With continuous delivery of energy at the level of the CBIGVs, the mean temperatures were 18.5 C (2 seconds), 18.6 C (5 seconds), and 19.1 C (10 seconds) (P < .05). Post hoc t tests found that values after 10 seconds of continuous activation were significantly greater than baseline values (P < .05). No significant correlations were found between the distance of the CBIGVs and temperature. For the distance and activation time parameters (Table 2), the baseline temperature at the level of the sciatic nerve was 20.6 C. With the energy probe at a distance of 10 mm, significant temperature changes were found (P < .01). The temperature increased to 21.0 C with 2 seconds of activation (P < .05), to 21.8 C with 5 seconds of activation (P < .01), and to 21.8 C with 10 seconds of activation (P < .01). With the energy probe at a distance of 5 mm, significant temperature changes were found (P < .01). The temperature increased to 21.6 C with 2 seconds of activation (P < .01), to 22.3 C Table 2. Fluid Temperature Assessed at Sciatic Nerve at Different Intervals of Distance and Duration Fluid Temperature ( C) Activation Time 0s 2s 5s 10 s
10 mm From Sciatic Nerve 20.6 (20-21) 21.0 (20-22) 21.8 (21-24) 21.8 (21-23)
5 mm From Sciatic Nerve 20.6 (20-21) 21.6 (20-23) 22.3 (21-25) 22.6 (21-24)
3 mm From Sciatic Nerve 20.6 (20-21) 21.8 (21-23) 22.8 (21-25) 23.7 (22-28)
NOTE. Data are presented as mean (range) for the 10 specimens.
RADIOFREQUENCY AND DEEP GLUTEAL SPACE
with 5 seconds of activation (P < .01), and to 22.6 C with 10 seconds of activation (P < .01). With the energy probe at a distance of 3 mm, significant temperature changes were found (P < .01). The temperature increased to 21.8 C with 2 seconds of activation (P < .01), to 22.8 C with 5 seconds of activation (P < .01), and to 23.7 C with 10 seconds of activation (P < .01).
Discussion Our results showed that the temperature in the sciatic nerve was not significantly increased after 2, 5, and 10 seconds of continuous activation of the TAC-S monopolar RF device on adjacent vessels. The tissue in contact with the RF probe itself may absorb most of the energy from the probe, thereby preventing an increase in fluid temperature. Obrzut et al.11 tested the temperature increase when applying the TAC-S probe in sheep capsular tissue prepared at 37 C. They found that the temperature at 1.5 mm was always less than 45 C. The distance of the CBIGVs to the sciatic nerve in our study ranged from 4 to 14 mm and showed no correlation with temperature at 2, 5, or 10 seconds of activation. After activation of the RF probe without touching any tissue, the maximum temperature at 3 mm with 10 seconds of continuous activation was 8 C (20 C to 28 C). This temperature elevation appears to be safe to the sciatic nerve. Experiments in animals have shown nerve changes with higher temperatures and longer periods of heating exposure. Wondergem et al.8 performed heat treatment of rat sciatic nerves and reported functional loss occurring after 58, 32, and 12 minutes of heating at 43 C, 44 C, and 45 C, respectively. Complete recovery occurred in all rats after 4 weeks. Hoogeveen et al.7 observed that hyperthermic injury for 30 minutes at 45 C slowly affected both motor and sensory function, taking about 7 hours until maximum dysfunction occurred. Motor function recovered completely within 9 days. Monafo and Eliasson12 related an apparently irreversible conduction block in 67% of tibial nerves after exposing rat sciatic nerves to 47 C for 30 seconds. The thermoprotective effects of irrigation to neural structures have been suggested by Donzelli et al.10 after experiments with bipolar cautery in sciatic nerves of rats. Irrigation fluid reduced the temperature response during the 15 seconds after the stimulation with bipolar cautery. Irrigation also reduced the degree of paresis and neuropathological changes when compared with a non-irrigation group. Thermic nerve injury using RF energy for capsular shrinkage has been a concern in shoulder arthroscopy.11,13-16 Zoric et al.4 studied the temperature profile associated with a bipolar RF ablation device within the glenohumeral space. The temperature profile was not apparently influenced by the voltage, and the flow rate was considered the most significant predictor of intra-
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articular temperatures. In a scenario of no flow (both the RF suction and the inflow were off), temperatures higher than 50 C were found in 12% of cases after 5 seconds of activation. In conditions of fluid inflow and no suction, the authors measured a mean temperature of 25 C at 3 mm after 10 seconds of activation. In our study the mean temperature was 23.7 C (range, 22 C to 28 C) at the same distance and time of activation. This difference may be related to the maintenance of fluid outflow in our study, even though we did not use suction. When inflow was on, Zoric et al. also observed a mean temperature lower than 30 from 0 to 120 seconds of continuous activation. We used continuous inflow and outflow of saline solution during all tests to reproduce the surgical technique used in deep gluteal space procedures.2 Whereas the maximum tested time of activation was 10 seconds in our study, other authors tested the temperature up to 120 seconds.3,4 We wanted to reproduce a practical scenario, in which less than 5 seconds of continuous activation is necessary to coagulate small vessels in the deep gluteal space in our experience. Our standard approach to vessel cauterization is one 3-second interval with continuous irrigation, followeddif necessarydby a second 3-second interval maintaining continuous irrigation. In an in vivo scenario, we noted that 3 seconds of activation allows a good contraction of the collagen of the vessel to control bleeding. For vessels larger than 2 mm, a ligature is used rather than a longer activation time. Fluid inflow comes through the arthroscope during arthroscopy and may be different depending on the cannula and arthroscope design.4 Although we did not observe a difference between multi-fenestrated and non-fenestrated arthroscopic cannulas in a preliminary study, we used a 70 arthroscope delivering unidirectional flow during all tests. With this type of arthroscope, the center of view does not match the inflow direction, and most of the inflow is not directed to the RF probe. Arthroscopes of 30 and distinct arthroscopic cannulas may have a different effect on the fluid temperature when activating RF devices. The RF devices can be monopolar or bipolar. The monopolar devices have a single active electrode, and the current is dissipated by a grounding pad. The bipolar devices have 2 active electrodes, the first for delivering the current and the second for returning the current.5 We used monopolar TAC-S probes in this experiment because the adjustable bending tip allowed more precise positioning at the CBIGVs and sciatic nerve. We could not satisfactorily access the points of interest using larger and/or unbendable bipolar RF devices. Considering the temperature assessment, we also could not position the regular thermocouples at the CBIGVs and sciatic nerve. TAC-S probes were used for temperature measurement, considering that a thermocouple is present in the tip of these devices. Moreover,
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equivalent temperature measurements between the TAC-S and regular thermocouple probes were observed in a preliminary study. Lu et al.17 have already described differences in tissue temperature effects depending on the type of RF device. The TAC-S probe is a temperature-controlled monopolar device, with the power of delivered RF energy determined by the temperature measured at its tip by a thermocouple. Although the continuous activation of the RF monopolar probe for 2, 5, and 10 seconds over vessels adjacent to the sciatic nerve was safe to this nerve in this study, the results cannot be extrapolated to other RF devices. Limitations This study presents a number of limitations to be considered when interpreting the results. First, histologic and electrophysiological sciatic nerve changes provoked by RF energy were not evaluated in this in vitro study. However, studies in animals have already related functional and histopathological changes according to the amount of heating.6-9,12 A second limitation relates to the reliability of the distance measurement under an endoscopic view. We used a 70 arthroscope with frequent changes in the direction of view to increase the accuracy. In addition, before each set of activation at 3, 5 and 10 mm of distance from the control probe tip, the energy probe tip touched the marks on the control probe to confirm that they were on the same plane. A third limitation applies to the fact that the distance between the arthroscope and the energy probe was not objectively controlled using a view from another arthroscope, and this factor may influence the irrigation from the arthroscope to the TAC-S. Lastly, considering that cadaveric tissue temperature is lower than in vivo temperature, colder CBIGVs could minimize the temperature increase in the sciatic nerve. Nevertheless, the TAC-S is a temperature-controlled device, and cooler tissue increases the RF generator output.
Conclusions This study found the tested monopolar RF device to be safe during use in vessels around the sciatic nerve after 2, 5, and 10 seconds of continuous activation. The maximum fluid temperature (28 C) after 10 seconds of activation at 3 mm of distance is lower than the minimal reported temperature necessary to cause nerve changes (40 C to 45 C).
References 1. Martin HD, Hatem M, Palmer IJ. Endoscopic sciatic nerve decompression: Operative technique. Oper Tech Sports Med 2012;20:325-332.
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