In vivo measurements of medial branch nerve depth and adjacent osseous structures for ablation of facet-related back pain: Predictors for patient candidacy

Hannah Zwiebel; Ron Aginsky; Arik Hananel; Daniel Baldor; Michael Gofeld; Jean-Francois Aubry; Suzanne D LeBlang

doi:10.1016/j.xnsj.2020.100018

In vivo measurements of medial branch nerve depth and adjacent osseous structures for ablation of facet-related back pain: Predictors for patient candidacy

N Am Spine Soc J. 2020 Aug 7:3:100018. doi: 10.1016/j.xnsj.2020.100018. eCollection 2020 Oct.

Authors

Hannah Zwiebel¹, Ron Aginsky², Arik Hananel², Daniel Baldor¹, Michael Gofeld³, Jean-Francois Aubry⁴, Suzanne D LeBlang⁵

Affiliations

¹ University of Miami Miller School of Medicine MD/MPH Program, 1600 NW 10th Ave #1140, Miami, FL 33136, United States.
² FUSMobile, 2972 Webb Bridge Road, Alpharetta, GA 30009, United States.
³ Silver Medical Group, Centre for Pain Relief, 4646 Dufferin Street North York, M3H 5S4 Canada.
⁴ Physics for Medicine Paris, Inserm, ESPCI Paris, CNRS, PSL Research University, 17 rue Moreau, Paris, 75012 France.
⁵ Focused Ultrasound Foundation, 1230 Cedars Court Suite 206, Charlottesville, VA 22903, United States.

Abstract

Background: Medial branch (MB) targeting during RF ablation for facetogenic back pain is usually performed with flouroscopic guidance yet no specific measurements on the target depth have been published. In order to understand candidacy for other potential ablation methods, we sought to determine the actual MB depth and measurements of adjacent osseous structures.

Methods: CT scans without contrast of the lumbar spine performed in the supine position were retrospectively analyzed in 100 patients. Axial slices less than or equal to 2.5 mm with sagittal and coronal reformations were evaluated. The following distances were measured bilaterally at the L2-L5 levels: The depth from the skin to the MB nerve (anatomic target for RF ablation) at a 15° angulation, the smallest width of the pedicle, and the length, height and width of the transverse process. Age, gender, weight, height, and BMI were correlated with the above measurements.

Results: The average distance and 95% CI from skin-to-MB in mm at a 15°angle to the skin increased as the lumbar level increased measuring 64.4 (62.4-66.5) at L2, 72.0 (69.7-74.3) at L3, 79.2 (76.9-81.6) at L4, and 79.1 (76.7-81.5) at L5. The average thickness of the pedicles also increased as the lumbar level increased measuring 9.2 mm at L2 and 16.1 mm at L5. Body weight, lumbar level, and female gender were associated with increased MB depth. Taller stature was associated with more superficial MB depth. We eliminated mild interaction effects between height, weight, and gender by substituting BMI for height and weight without affecting r². Linear regression revealed the following equation: MB Depth (mm) = 2.2*BMI + 4.9*lumbar vertebral level + 3.6 (if female) - 5.4, which fit the data well (P<0.001, r² = 0.60).

Conclusions: Our results demonstrate that the MB resides 107 mm or less in depth when measured at a 15° angulation from the skin in > 95% of patients and the distance increases as the lumbar level increases.

Keywords: Facetogenic back pain; Medial branch nerve; RF ablation; Thermal ablation.