12 Nerve variability Limited success in pain relief for SIJS has been attributed to the variability of the courses of lateral branch nerves, as well as continued debate over the exact innervation of the SIJ [17]. The anterior portion of the SIJ is believed to be innervated by the posterior rami of L1–S2, with possible additional innervation from the obturator nerve, superior gluteal nerve, and lumbosacral trunk, while the posterior portion of the SIJ is believed to be innervated by the posterior rami of L4–S3 [22]. Radiofrequency neurotomy has targeted the L5 dorsal ramus and its branches to the SI joint, as well as the lateral branches of the S1–S3 dorsal rami. Clearly, not all possible nerves that can contribute to SI joint pain are targeted by this procedure [19]. Interest- ingly, radiofrequency neurotomy targets the dorsal rami and is thus more effective for extra-articular rather than intra-articular joint pain, since there is no known anterior innervation to the dorsal SIJ ligamentous complex [19]. Although radiofrequency neurotomy is performed on dor- sal rami, nerve blocks to conﬁrm SIJ pain are not done on dorsal rami because injected anesthetics are limited by fascia and ligaments in that area. Therefore, conﬁrmatory blocks are approximated by injecting intra-articularly [19, 21]. In addition, nerves may take circuitous routes in dif- ferent people, leading to difﬁculty in targeting the exact location of nerves during the radiofrequency neurotomy procedure. In fact, in a cadaveric study by Yin, the number and location of sacral lateral branch nerves varied mark- edly, and nerves more often than not took an indirect path to the SI joint complex [21]. Techniques such as sensory stimulation-guided radiofrequency neurotomy have been developed to overcome such individual variability and to protect nearby vessels and other neural structures [21, 23]. Sensory-guided radiofrequency neurotomy involves using minimal threshold stimulation voltages to cause a local sensory response, which allows for better identiﬁcation of symptomatic (pain transmitting) versus asymptomatic (non-pain transmitting) nerves. Yin et al. [21] points out that the negative study by Ferrante did not use sensory stimulation. Teaching texts have suggested performing radiofre- quency lesions at the superior lateral portion of the S2 and S3 foramina, at the medial branches of the higher dorsal rami in the lumbar region, at the sacral ala and SIJ junction, and along the posterior SIJ long axis. However, Vallejo asserts that there are no evidence-based studies to support such targets [22]. In the positive-outcome studies on radiofrequency neurotomy reviewed by Hansen, one used contiguous strip lesions (contiguous lesions produced between two probes) at the lateral dorsal foraminal aperture plus monopolar lesioning (lesion produced by one probe) at Curr Rev Musculoskelet Med (2009) 2:10–14 the L5 dorsal ramus, one targeted the sacral lateral branch using sensory-stimulation guiding, and one targeted the L4–L5 primary dorsal rami and S1–S3 lateral branches. The study by Vallejo, which achieved positive short-term but negative long-term results, used pulsed lesioning at the medial branch of L4, the posterior primary rami of L5, and the lateral branches of S1 and S2 [2]. The study by Ferr- ante, which achieved negative short-term and long-term results targeted the SIJ line, which Yin et al. [21] asserts is located laterally from where one can access the lateral branch nerves, since they are embedded within dense ligaments. Technique In addition, some investigators have asserted that some negative results for radiofrequency neurotomy of the SI joint can be attributed to poor procedure technique. As mentioned above, radiofrequency neurotomy lesions dorsal branches of the SIJ, which are extra-articular, not intra- articular. Lesions of these branches can be made in several fashions. Pino et al. studied the correct parameters of radiofrequency ablation and found that practitioners could create contiguous strip lesions when they placed the can- nulae 6 mm or less apart, while they could create unipolar lesions if the cannulae were spaced more than 6 mm apart. They found that optimal technique to maximize the surface area of the lesion was created when the cannulae were positioned parallel to each other, 4 to 6 mm apart, and temperature was held at 90 C for 120–150 s [24]. Vallejo used pulsed radiofrequency neurotomy (PRFN) to decrease maximum temperatures and risk of adjacent tissue destruction [22]. In PRFN, needles should be placed perpendicular to the nerve, where the electrical ﬁeld cre- ated is greatest. Non-PRFN, however, uses parallel positioning because the lesion is created at the tissues surrounding the needle [22]. Vallejo et al. asserts that Ferrante’s negative results may have been due to perpen- dicular positioning of a non-PRFN technique [22]. Indeed, because radiofrequency neurotomy creates relatively small lesions, the positioning of the electrode to the target neural tissue is critically important [21]. Finally, some investigators have targeted particular branches of particular rami, while Burnham and Yasui in a less technically complicated method used a series of bipolar strip lesions adjacent to the lateral dorsal foraminal aperture plus conventional monopolar lesioning at the L5 dorsal ramus, with positive results. Efﬁcacy Percutaneous radiofrequency neurotomy has been found in the literature to have utility in relieving SIJ pain. Hansen