LETTERS TO THE EDITOR ARTHROGENIC PAIN To the Editor: It was interesting to read the technical communica- tion titled “Intra-articular Application of Pulsed Radiofrequency for Arthrogenic Pain—Report of Six Cases.” 1 The authors start with the introduction that invasive treatment of chronic pain emanating from joints is often difficult because of the complex anatomy of the nerve supply. However, they lump in spinal facet joints, which includes cervical facet joints and atlanto-axial joints in the shoulder. They failed to explain the mechanism of action of intra-articular application of pulsed radiofrequency, either in cervical facet joints, the atlanto-axial joint, knee joints, the sacroiliac joint, or the shoulder. If we understand correctly, the needle is positioned in at one place in the joint and then a pulsed radiofrequency of 45 V is applied for 10 minutes. This fails to explain the mechanism of action. It needs to be clarified if the mechanism of pulsed radiofrequency is denervation of the nerve supply or the heating of the joint. If the den- ervation of the nerve supply is the mechanism, the readers are very much interested in knowing how den- ervation can be achieved by placing the needle in one place. Further, the authors have used pulsed radiofre- quency for 10 minutes in the cervical facet joint, knee joint, sacroiliac joint, radiocarpal joint; whereas, for shoulder and atlanto-axial joint, 8 minutes of pulsed radiofrequency was utilized. Even though there was variation in the voltage, this does not explain the rationale of 40 V applied for 8 minutes in the shoulder and 45 V applied for 10 minutes in cervical facet joint. Overall, even though this is a technical report, it has substantial consequences on interventional pain man- agement with potential abuse of the technology. At the present time, pulsed radiofrequency is considered as experimental even for medial branch nerves and other peripheral nerves. Laxmaiah Manchikanti, MD Pain Management Center of Paducah, Paducah KY E-mail: drlm@thepainmd.com Vijay Singh, MD Pain Diagnostic Associates, Niagara WI 54151, U.S.A. E-mail: vj@wmpnet.net REFERENCE 1. Sluijter ME, Teixeira A, Serra V, Valgo S, Schianchi P. Intra-articular application of pulsed radiofrequency for arthrogenic pain—Report of six cases. Pain Pract. 2008;8:57– 61. Editorial note: While the experimental nature of the technical report was already stated in the cited article, we are grateful to Drs Manchikanti and Singh for providing the opportu- nity to emphasize this point. CTH Reply to Drs. Manchikanti and Singh: We thank Dr. Manchikanti for his interest in our article. 1 As for the mode of action of pulsed radiofre- quency (PRF) in this procedure, we have tried to explain our views in the discussion part of the article. At no point have we suggested that any form of denervation could be involved, and this is of course quite obvious. The mean tip temperature stays well within limits, espe- cially when a pulse width of 10 milliseconds is used. Thermal fields during heat spikes and electric fields only reach potentially destructive levels in very close prox- imity (<0.1 mm) to the electrode. Denervation––or, more explicitly, damage––can therefore be excluded as an explanation. We find this a positive development, because it brings clarity. When PRF was introduced it was suggested that this was a nondestructive method. We now know that this is not true. There is a mild degree of destruction, 2 probably because of either heat spikes or strong electric fields during the pulse. 3 It has been suggested that this “mini-destruction” might play a role in the mode of action of PRF. This view cannot be held if intra-articular PRF is effective. We therefore have to turn elsewhere to find the mode of action. The two systems that govern pain processes are the nervous system and the immune system. These systems are intimately related, up to the point that an action on one system implies a sequence in the © 2008 World Institute of Pain, 1530-7085/08/$15.00 Pain Practice, Volume 8, Issue 3, 2008 217–219