Linea alba (Latin ‘white line’) is a tendinous, fibrous raphe that runs vertically down the midline of the abdomen. It extends between the inferior limit of the sternum and the pubis, separating the rectus abdominis muscles. In leaner, more muscular individuals, it is visible externally as a longitudinal, shallow groove.
Even though the linea alba is not a muscle, Terminologia Anatomica lists it under abdominal muscles. Why would that be? It’s because the linea alba is formed by the interlacing aponeuroses of three vertical abdominal muscles: external oblique, internal oblique and transversus abdominis muscles.
Read on if you would like to learn more about the anatomy, relations and function of the linea alba.
|Origin||Tip of xiphoid process|
|Insertion||Anterior fibres: pubic symphysis
Posterior fibres: pubic crests on both sides
|Structure||Formed by aponeuroses of external oblique, internal oblique and transversus abdominis|
|Function||Attachment site for:
- Fundiform ligament of penis
- Pyramidalis, internal oblique, external oblique and transversus abdominis muscles
- Parietal peritoneum via extraperitoneal connective tissue
Linea alba originates from the tip of the xiphoid process of the sternum and extends inferiorly along the midline of the whole abdomen.
This fibrous raphe has a dual insertion at the level of the pubis. The superficial fibres of the linea alba insert into the pubic symphysis. In turn, its deep fibres form a membranous triangular lamella posterior to the rectus abdominis muscle, which represents the posterior attachment of linea alba. This structure fans out to insert into the pubic crests on both sides.
The aponeuroses of internal oblique, external oblique and transversus abdominis muscles extend vertically across the anterior aspect of the abdomen. While crossing over to the opposite side, their aponeurotic fibers interweave along the midline of the abdomen, forming the thickening known as the linea alba at the decussation. This interlacing takes place between matching layers (e.g. superficial-to-superficial, deep-to-deep) of corresponding muscles (e.g. external oblique-to-external oblique) and also between different muscles (external oblique-to-internal oblique). In addition, the various aponeurotic layers (superficial, intermediate, deep) are also intertwining between them.
Linea alba generally lacks blood supply and innervation, but a few small blood vessels cross to the opposite side over its anterior surface. Due to this, it is a common incision and puncture site in abdominal surgery and suprapubic bladder catheterization, respectively.
The umbilicus is located slightly inferior to the midpoint of the linea alba, separating the latter into two halves: a wider, supraumbilical part and a thinner, infraumbilical part. The linea alba is widest around the umbilicus. Its width and thickness also vary depending on weight, age and sex - it is wider and thinner in overweight individuals, people past their 50s and women, especially those with a history of multiple advanced pregnancies.
Relations and function
Linea alba separates the rectus abdominis muscles in the midline. It is also an attachment site for several structures and muscles:
- Fundiform ligament of penis
- The small pyramidalis muscle, which tenses the linea alba. The importance and true function of this action are still questioned.
- Anterior abdominal muscles whose aponeuroses form the linea alba: internal oblique, external oblique and transversus abdominis.
A few tendinous structures in the surrounding area have fibers which blend with the linea alba:
- Upward directed medial fibers from the inguinal ligament, close to its attachment.
- Extraperitoneal connective tissue anchors the parietal peritoneum to the linea alba.
- The overlying membranous layer of abdominal subcutaneous tissue (Scarpa’s fascia) of the anterior abdominal wall blends with the linea alba in the midline. The fatty layer of abdominal subcutaneous tissue (Camper’s fascia) is located on top of the membranous layer and is continuous over the linea alba, whereas the deep adipose layer is absent at the fusion site between the membranous layers and the linea alba.