Friday, March 28, 2014

The "correction index" as a measure of severity of pectus excavatum.

Pectus excavatum is a condition where the sternum and adjacent ribs develop in an abnormal way, resulting in a depression in the middle of the chest.  The consequences of the depression are mainly esthetic, but may affect lung and cardiac function (controversial evidence)
Figure 1

The Haller index (Figure 1) has been classically used as a measure of the severity of the pectus deformity, where a HI >3.25 is considered an indication for consideration for surgical correction.

An innate fault of this measurement, as St Peter et al pointed out in their paper, is the fact that this number relies heavily on the cross sectional diameter of the chest (Figure 1; measurement a), which varies between patients.  They noted that when they measured the HI in patients with a pectus deformity, there was a 45% cross-over with normal patients. Essentially, the authors suggest that the HI is not a reliable measure of severity of a pectus deformity.
Figure 2

As an alternative, the authors recommend using a measurement they referred to as the correction index (Figure 2).  Simply put, CI is the ratio of the anticipated rise in the sternal defect after bar placement (Figure 2; measurement a-b), to the maximal anterior to posterior dimension of the inner chest, multiplied by 100.

The question then becomes, what CI should be used as an indication for surgery?  The authors suggested that a 10% or higher CI reflects a pectus deformity severe enough to warrant correction.

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