Anatomical and functional relationships between external abdominal oblique muscle and posterior layer of thoracolumbar fascia.

The abdominal muscles are important for the stability of the lumbar region through the thoracolumbar fascia (TLF). However, there is not full agreement regarding the posterior transversal continuity of the external abdominal oblique muscle (EO) with the TLF. To clarify this point, 10 cadavers and computed tomography (CT) images from 27 subjects were used to evaluate the transversal continuity of the TLF with the abdominal muscles. The width of the fascial continuity of the EO with the posterior layer of TLF along the posterior border of the EO was also measured (40.70 ±3.92 mm). The epimysial fascia of the EO was in direct continuity with the posterior layer of TLF in eight cadavers and 23 CT images, whereas in two cadavers and four CT images, the epimysial fascia of the EO first fused with the fascia covering the latissimus dorsi, and then, both fasciae were in continuity with the posterior layer of TLF. Therefore, the transversal fascial continuity of the EO could explain the transmission of tension from the EO to the posterior layer of TLF and its importance in maintaining the stability of the lumbar spine through a hydraulic effect. Regarding fascial continuity in the trunk, and taking the EO into consideration, the TLF is formed by the fascia of all the abdominal muscles as the rectus sheath. In this manner, myofascial continuity between the TLF and the abdominal muscles is achieved through the aponeurosis and fascia, which ensures synchronization between the erector spinae and the rectus abdominis. Clin. Anat. 31:1092-1098, 2018.