Component separation index

Last revised by Vikas Shah on 5 Jan 2023

The component separation index is a value used to quantify the degree of diastasis of the rectus abdominis muscles in the context of anterior abdominal wall hernias.

The mode of repair of midline abdominal wall hernias (often incisional hernias through laparotomy wounds) depends on the degree of diastasis of the rectus muscles, which must be reapproximated in order to repair the hernia 1. Simplistically, the further the rectus muscles are apart, the greater the tension would be if they were to be reapproximated directly, and therefore the greater the likelihood of failure of repair without the use of additional techniques or mesh placement to bridge the gap 1.

On the axial CT slice that shows the hernia orifice at its widest, lines are drawn from the medial edges of the rectus abdominis muscles to meet at a point on the anterior wall of the aorta. The angle between these two lines is the angle of diastasis. The component separation index is the angle of diastasis divided by 360° 2.

Values above 0.21 tend to increase the likelihood of requiring interpositional mesh repair 2. However, the requirement for this depends on several additional variables, so this is not a hard and fast cut-off.

The component separation index was first described by Michael Christy, an American plastic surgeon, and colleagues in 2012 2.

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Cases and figures

  • Case 1: CSI < 0.2
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