https://orcid.org/0000-0002-4580-1173
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Daniel M Cushman, Nicholas Monson, Aaron Conger, Richard W Kendall, A Michael Henrie, Zachary L McCormick, Use of 0.5 mL and 1.0 mL of Local Anesthetic for Genicular Nerve Blocks, Pain Medicine, Volume 20, Issue 5, May 2019, Pages 1049–1052, https://doi.org/10.1093/pm/pny277
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Recent literature has identified a high false-positive rate of genicular nerve blocks in predicting successful outcome of genicular nerve radiofrequency ablation (RFA) [1]. A new cadaveric study has confirmed a greater number of nerves contributing to the sensory innervation of the anterior knee joint capsule compared with those targeted by genicular nerve RFA—the superior lateral, superior medial, and inferior medial genicular nerves [2–4]. Because the volume of monopolar radiofrequency lesions has been found to range from 0.5 to 1 cm3 in ex vivo bovine liver [5], depending on electrode type (cooled vs conventional), size, and lesioning parameters, these additional nerves identified would not be captured in the burn radius if a single monopolar lesion were created at each target genicular nerve site [1–4]. Additionally, using specific amounts of contrast medium in place of anesthetic in two separate patients, Figure 1a–d (0.5 mL of contrast medium) demonstrates spread beyond the boundaries of typical 0.5- and 1-cm3 monopolar RFA lesions. Further, many providers utilize 1-mL diagnostic anesthetic block volumes [1,2,4], which cover an even greater territory. Figures 1–3 suggest that depending on individual variations in nerve location [3], both the articular branch of the common fibular nerve and the nerve to the vastus medialis are likely anesthetized by 1.0 mL and may also be anesthetized by 0.5 mL of local anesthetic; however, both of these nerves may not be captured by a monopolar radiofrequency lesion in most cases using common protocols [1,2,4]. Additionally, a 1.0-mL volume diagnostic block likely anesthetizes the superior medial genicular nerve, but this nerve may not be captured by a monopolar radiofrequency lesion in some cases using common protocols [1,2,4].
