• Haesun Jung, Junyeol Bae, Jungsoo Kim, Yongjae Yoo, Ho-Jin Lee, Hyungsang Rho, Andrew Hogyu Han, and Jee Youn Moon.
• Department of Anesthesiology and Pain Medicine, Chung-Ang University Hospital, Seoul, Republic of Korea.
• Pain Med. 2022 Sep 30; 23 (10): 1670-1678.

ObjectiveWe investigated the thoracic segment corresponding to the inferior margin of the rhomboid major muscle (RMM) using ultrasound (US) to evaluate its potential as a reliable anatomic landmark for segment identification.DesignA prospective observational study.SettingAn operating room.SubjectsPatients who underwent procedures around the thoracic spine.MethodsFour hundred segments corresponding to the RMM's inferior margin were identified through the use of paravertebral sagittal US and confirmed by fluoroscopy in 100 participants in the prone position with upward and downward shoulder rotation, comprising four datasets (up-right, up-left, down-right, and down-left). The US identification of the RMM's inferior margin was dichotomously scored (clear vs ambiguous). Each dataset was divided into two groups (dominant segment group vs remaining segments group), which were compared. Factors relevant to the dominant segment associated with the RMM's inferior border were determined through univariable analyses.ResultsThe T6 segment was observed most commonly (59.5%) along the RMM's inferior border on paravertebral sagittal US acquired in the prone position, followed by T5 (25.0%), T7 (12.8%), and T4 (2.7%). The segments corresponding to the RMM remained unchanged by shoulder posture in most participants (n = 74, 74%). The RMM's inferior border was clearly distinguishable in 330 cases (82.5%). When the RMM's inferior border was clearly identified, the corresponding segment was likely to match T6 in all datasets, with odds ratios ranging from 3.24 to 6.2.ConclusionsThe RMM's inferior border over the transverse process corresponded to T6 most frequently on paravertebral sagittal US, and its deep fascia was clearly visible in most cases.© The Author(s) 2022. Published by Oxford University Press on behalf of the American Academy of Pain Medicine. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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