The enigmatic subcostal muscle: Anatomical study with application to spine and chest pain syndromes and avoidance of confusion on imaging

The aim of this study was to revisit the morphological characteristics of the subcostal muscle and to obtain its morphometric data. One hundred and two sides of the thorax from 51 adult cadavers were used. The total number of subcostal muscles in the 102 specimens was 559. The subcostal muscle commonly comprised an aponeurosis at its superior and inferior attachments. This muscle had a thin band-like shape in 64.2% cases, while in the other 35.8% either its superior or inferior attachment was wider. It was classified into the following four types on the basis of its inferior attachment: in Types I and II it extended to two (79.3%) and three (12.0%) lower ribs, respectively; in Type III it joined adjacent muscles such as the psoas major (2.2%) or quadratus lumborum (0.7%); and in Type IV it was attached to the transverse process (0.4%) or body (3.9%) of the 12th thoracic vertebra and the body of the 1st lumbar vertebra (1.4%). The subcostal muscle was found at the deepest layer of the intercostal space, and mainly presented in the upper and lower parts of the thorax. Its width and height were 18.2±10.9 mm (mean±SD) and 56.0±13.3 mm, respectively. The distances from the midsagittal line to the superior and inferior attachments of the subcostal muscle were 77.1±13.0 mm and 48.9±13.5 mm, respectively. The results of this study will help to advance current understanding of the subcostal muscle.