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Sonographic Measurements of the Interscapular Soft Tissue for Rhomboid Major Trigger Point Injection in Thai
Jeeranan Khunachiva1, Pattarawit Promrak2, Phichayut Phinyo3
1Department of Rehabilitation Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand.
Background:
Trigger point injection of the rhomboid major carries a risk of pleural injury, which can be minimized with ultrasound (US) guidance. However, the US is not readily available in many clinical settings. This study aimed to establish practical margins for needle insertion into the rhomboid major to guide practice when US is not accessible.
Methods:
Healthy volunteers were recruited from January 2021 to August 2021. Anthropometric data were collected, and participants were classified into three body mass index (BMI) subgroups (<23, 23-24.9, >25 kg/m2). US examinations were performed in the sitting position. The rhomboid major was divided into two regions (A1, A2), skin-to-rhomboid (SR), rhomboid thickness (RT), and skin-to-pleural (SP) distances were measured bilaterally. Safe margins were defined as mean - 2 or 2.5 standard deviation of SP. Analyses included descriptive statistics, intraclass correlation coefficients (ICCs), t-tests, regression, and Pearson's correlation.
Results:
Eighty-four volunteers participated (43 males, 41 females; mean age 38.0 ± 10.7 years). Intrarater reliability was excellent (ICC 0.921-0.974). No side-to-side differences were observed. SR and SP distances increased significantly, and RT was thicker with higher BMI (P < 0.001). At A1, SR measured 13.2 ± 2.4 mm (normal), 15.7 ± 2.5 mm (overweight), and 19.1 ± 3.5 mm (obese); at A2, 11.1 ± 2.4, 13.9 ± 2.5, and 17.3 ± 3.6 mm, respectively. SR and SP correlated strongly with BMI (r = 0.733-0.793). Safe margins stratified by BMI and sex were provided.
Conclusion:
BMI-based reference values provide evidence-based guidance for safe trigger point injection into rhomboid major when US is unavailable, reducing risk of pleural injury.
