Patients and methods: This retrospective study was conducted with 1,015 participants (536 males, 479 females; mean age: 57.1±14.9 years; range, 18 to 95 years) between December 2017 and December 2019. The distances from the skin to the pleura and the skin to the muscle were measured at the reference points according to the literature for the upper trapezius and rhomboid major muscles from the chest computed tomography images of the patients. The midpoint of these two points was determined as a third point. In addition, the thinnest point in the medial of the scapula was determined as the fourth point, and depth measurements were made from these four points. Measurements were compared among groups stratified by age, sex, and body mass index.

Results: The measured depths from the skin to the muscle and the skin to the pleura significantly differed between groups (p<0.01). At three of the measurement points, the skin-to-pleura distances of females were shorter than that of males, while the skin-to-muscle distances were longer (p<0.01). The mean, minimum, and maximum values of the depths were determined for the groups.

Conclusion: We recommend clinicians who apply injection to the parascapular region consider the patients' age, sex, and body mass index. The tables provided in this study may help guide clinicians performing the procedure. Keywords : Appropriate depth, dry needling, pneumothorax, rhomboid major, trigger point, upper trapezius