Arcuate Line · What Is It, Clinical Significance and More

The arcuate line, also known as the semicircular line of Douglas, is a curved line found posterior to the rectus abdominis muscle bilaterally, between the umbilicus and the pubic symphysis. This anatomical finding may not always be present, and its exact position may vary.  

Superior to the arcuate line, the external oblique aponeurosis (i.e., a thin layer of connective tissue that covers and supports the muscle) passes anterior to the rectus abdominis muscle. The aponeurosis of the internal oblique splits to surround the rectus abdominis muscle. Additionally, posterior to the rectus abdominis muscle is the aponeurosis of the transversus abdominis muscle, as well as the transversalis fascia. All of the aforementioned aponeuroses wrap around the rectus abdominis muscle, forming the rectus sheath. At the level of and posteriorly to the arcuate line, the aponeuroses of the internal oblique and transversus abdominis pass anteriorly to the rectus abdominis muscle, instead of surrounding the muscle. Therefore, the transversalis fascia is the only structure located posteriorly. 

The arcuate line is usually located at about one-third of the distance from the pubic crest to the umbilicus. However, the exact position of this line may vary; it has also been located as superior as the umbilicus, or as inferior as the public symphysis. 

The arcuate line is an anatomical structure of great clinical significance, especially for surgeons. It may be the site of weakness in the abdominal wall through which abdominal hernias may form. For example, Spigelian hernias develop between the lateral border of the rectus abdominis muscle and the linea semicircularis (i.e., the bilateral vertical curved lines in the anterior abdominal wall where the rectus sheath layers fuse laterally to the rectus abdominis muscle). They typically protrude through the transversus abdominis aponeurosis, very close to the level of the arcuate line. Notably, individuals without the arcuate line are less likely to develop a ventral hernia. 

In addition, the arcuate line is the location where the inferior epigastric vessels perforate the rectus sheath, to supply blood to the inferior portion of the anterior abdominal wall.

The arcuate line, also known as the semicircular line of Douglas, is a curved line found posterior to the rectus abdominis muscle bilaterally, at about one-third of the distance between the umbilicus and the pubic symphysis. This anatomical finding may not always be present, and its position may vary. However, when present, the arcuate line is of great clinical significance, especially for surgeons, as Spigelian hernias usually present close to the arcuate line. Additionally, the arcuate line indicates where the inferior epigastric vessels perforate the rectus sheath.