Reply to Letter to the Editor regarding “Quantification of needle angles for traditional lumbar medial branch radiofrequency ablation: an osteological study”

Dear Editor We thank Rivers et al. for their interest in our paper.1 As researchers and academics, we are informed by science and grounded in evidence. With controversy, careful re-inspection and validation is required. Therefore, using 3D modeling technology, available to our team, we have confirmed the observation by Rivers et al. In the 2004 landmark paper published by Lau et al., it was stated that to achieve parallel placement with the medial branch, “the electrode must lie obliquely, at about 20° from the sagittal plane.”2 The authors also stated to obtain an end-on or decline view, “the X-ray beam was tilted laterally by 20° from an AP view and then declined steeply along the length of the body until a view was obtained along the course of the electrode.” This decline view would correspond with the coaxial or pillar view which some spine interventionalists use to advance the needle. This description likely led to the unexamined assumption that the angle away from the sagittal plane approximates the oblique angulation of the fluoroscope when acquiring the coaxial view. This is evidenced by educational content referencing Lau et al. that demonstrated ending positions of the fluoroscope, in pillar view, approximates needle angles measured in posterior and lateral radiographs.3 We would like to acknowledge Rivers et al. for their critical appraisal of an unexamined assumption in the field of fluoroscopic guided lumbar medial branch denervation. Regarding their suggestion to correct our study’s means and histograms using the transformed data, it is important to note that the angles reported in our study reflect needle angles measured in the direct posterior and lateral views. These needle angles should not change as the measurements were based on standardized anatomical images using common fluoroscopic practices (ie, squared endplates). Therefore, these are the needle angles that spine interventionalists would expect to see as they view standardized posterior and lateral radiographs when the needles are placed parallel along the middle two-quarters of the lateral neck of the superior articular process. We believe Rivers et al. meant to suggest that a new dataset reporting the transformed oblique angles (based on our reported needle angles in posterior and lateral views) should be included which would represent the angulation required to obtain coaxial view. This is where their trigonometric formula would be of use. However, based on our research,1,4 the substantial cranial-to-caudal angulation required to achieve a parallel needle placement limits the ability to use a coaxial approach. Recognizing this limitation, we sparingly use this coaxial approach clinically and are in the process of conducting/preparing a case series publication to provide more details regarding our needle placement technique that has resulted in positive outcomes. We appreciate the comments by Rivers et al., as it highlights the impact anatomical research can have on the field of interventional pain medicine. Continued anatomical research support and collaboration between societies, clinicians, and anatomists will help in re-evaluating principles, question unexamined assumptions, and optimize interventional pain procedures. None declared. Conflicts of interest: None declared.

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