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Interv Pain Med
Interv Pain Med
Interventional Pain Medicine
2772-5944
Elsevier

S2772-5944(22)00070-X
10.1016/j.inpm.2022.100079
100079
Commentary
Physical examination tests technical accuracy of sacral lateral branch RFN
Bogduk Nikolai nbogduk@bigpond.net.au

The University of Newcastle, Newcastle, Australia
04 3 2022
3 2022
04 3 2022
1 1 100079© 2022 The Author
2022
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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pmcAt lower cervical and lower lumbar segmental levels the medial branches of the dorsal rami typically do not become cutaneous. Consequently, numbness has not been a feature of concern following medial branch blocks or radiofrequency medial coagulation at these levels.

It is, therefore, understandable, to some degree, that testing for numbness has, in the past, not been part of the practice of sacral lateral branch blocks or sacral lateral branch radiofrequency coagulation. Indeed, none of the pioneering studies of these procedures paid attention to numbness. Yet, this is a curious omission, for it is well-established that the sacral lateral branches become the medial clunial nerves that innervate the skin over the buttock.

Moreover, numbness in the practice of spinal radiofrequency coagulation is not without precedent. The third occipital nerve becomes cutaneous, and numbness in the distribution of this nerve has served as a confirmatory test that third occipital nerve blocks [1] or third occipital nerve radiofrequency coagulation [2] has been technically adequate. Absence of numbness indicates that the target nerve has not been captured, and serves as a quality assurance check.

In this regard, the study of Vorobeychik et al. [3] fills an intellectual and professional vacuum in the practice of procedures that target sacral lateral branches. This contribution is long overdue, and is more significant that simply tidying up a corner of research.

In various ways, to various extents, practitioners and investigators alike have been concerned about the technical adequacy of techniques used to block sacral lateral branches or to coagulate them. As targets, these nerves are elusive. They cannot be captured using a single target point. Studies have shown that blocks at multiple sites and at multiple depths are required to fully anesthetize the sacral lateral branches [[4], [5], [6]]. Meanwhile, investigators have competed in promoting and comparing various techniques by which to capture the sacral lateral branches with radiofrequency coagulation [[7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32]].

The results of Vorobeychik et al. [3] resurrect a classical practice: examining the patient. Instead of arguing on theoretical grounds that their procedure is better than others at securing the lateral branches, physicians have at their disposal a test that can be applied immediately, in each and every patient.

Finding numbness is not a guarantee that a block or a coagulation will relieve the pain for which the patient was treated, but it is an indication that no technical failure has occurred, just as it is for third occipital nerve blocks or third occipital radiofrequency coagulation. If numbness does not occur, the lateral branches cannot have been properly captured. By applying this quality assurance test, physicians can tell if they have made a mistake in their execution of the procedure, instead of blaming the patient or the procedure for lack of a positive response.

Accordingly, testing for numbness should become a critical element of the operational criteria both for sacral lateral branch blocks and for sacral lateral branch radiofrequency coagulation. If numbness does not occur, the physician should revisit their execution of the procedure.

The results of Vorobeychik et al. [3] show that immediate relief of pain occurs significantly more often when patients incur numbness. Curious is the small proportion of patients who obtain relief without going numb; but it is pointless arguing about happened in these patients without additional data. A placebo-controlled trial would be required to determine if these constituted placebo responses.

What needs still to be determined is how long the analgesic effect of sacral lateral branch radiofrequency coagulation endures, and if any patients consider the associated numbness to be adverse. In the meantime this need underpins a second, addition to the operational criteria.

Patients undergoing sacral lateral branch radiofrequency coagulation should be informed that numbness in the buttock will be the price that they must pay in order to be relieved of their sacroiliac pain. A corollary flows from this association. Being completely numbed may be too high a price to pay for inadequate, partial relief of pain.
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