Anatomo-radiological Study on Semilunar Line as Risk Factor fo Diastasis Recti Abdominis

As usually described, at the lateral margin of the rectus sheath, the lateral muscles aponeurosis joins themselves in the semilunar line. The external oblique (EO) aponeurosis constantly passes in front of the rectus muscle (RM), composing the anterior lamina of the sheath. The internal oblique (IO) aponeurosis splits its fibers in an anterior and a posterior layer. The anterior layer joins the fibers of the EO in front of RM to constitute the anterior lamina. But some centimeters below the umbilicus, there is no split in the fibers, and all the aponeurosis of the IO join the EO and transverse aponeurosis in constituting the anterior sheath. The transverse muscle aponeurosis also behaves differently from cranial to caudal. Cranially the fibers constantly remain posterior to the RM and constitutes the deep layer of the sheath, but at a variable level some centimeters below the umbilicus, they go anteriorly will all other flat muscle aponeurosis.

During cadaveric dissections and in a careful evaluation of various CT abdominal wall images, we noted that the IO aponeurosis can join the rectus sheath in two ways: a) splitting its fibers in an anterior and posterior layer, as classically described, or b) joining only the posterior rectus sheath without an anterior layer.

To confirm our hypothesis, we design this multicenter cross-sectional observational study.

Data collection:

For each patient, together principal endpoints, following additional variables will be collected:

• Age
• Sex
• BMI
• Previous abdominal surgical procedures (type and date)
• Diabetes affection
• Number of pregnancies and multiple birth, date of delivery and type of delivery (vaginal or caesarean section)

CT evaluation

A researcher, trained by an expert radiologist, will evaluate the axial image of abdominal standard CT to identify and record:

• the internal oblique aponeurosis insertion in both side: classical double (anterior and posterior) insertion or only posterior insertion
• The inter-recti distance at three regions, including supraumbilical (4,5 cm above the umbilicus), periumbilical and subumbilical (4.5 cm below the umbilicus)
• The thickness and width of both rectus muscles
• The distance between lateral edge of the rectus muscle and the medial edge of the internal oblique muscle
• The distance between lateral edge of the rectus muscle and the medial edge of the external oblique muscle
• The distance between lateral edge of the rectus muscle and the medial edge of the transverse muscle
• Presence of abdominal wall hernia, if any

Definition and classification of DRA According Rath et al. (13) proposal, for subjects younger than 45 years, DRA will be defined as a separation of the two recti more than 1.0 cm above the umbilicus, 2.7 cm at the periumbilicus and 0.9 cm below the umbilicus; for subjects over 45 years, the corresponding values will be 1.5 cm, 2.7 cm and 1.4 cm, respectively. The presence of an inter-recti distance superior to the cut off value in two or three regions (supraumbilical, umbilical and subumbilical) in the same patient will be described as DRA.

Width of the DRA will be defined according Ranney (15) classification: an IRD \< 3 cm will be labeled mild diastasis, 3-5 cm IRD moderate diastasis and more than 5 cm severe diastasis.