The Depression Index: an objective measure of the severity of pectus excavatum based on vertebral diameter, a morphometric correlate to patient size.

BACKGROUND/PURPOSE: In patients with Pectus Excavatum (PEX), the proposed Depression Index (DI) is derived from the absolute measurement of sternal depression using the transverse vertebral body diameter as a surrogate for height. The previously described objective and useful Pectus Index (PI) and Correction Index (CI), utilize thoracic diameters and do not always reflect the severity of the deformity as observed by clinicians.

METHODS

Data for age, weight, height and vertebral diameter of T9, 10 and 11 were collected on 60 patients, with normal skeletons, undergoing CT scanning. The DI, PI and CI were calculated from CT scans on 76 patients with PEX. Indices were also compared to subjective rankings of the deformity from visual inspection of photographs by 5 clinicians.

RESULTS

All parameters of age, weight and height correlated with the vertebral diameter. The DI correlated with the severity of the PEX deformity as also measured by the PI and the CI. There was a better correlation of the observed deformity severity to the DI than the PI or CI.

CONCLUSION

There is a strong correlation between transverse vertebral size and patient height. The DI is an objective measurement of the severity of a PEX deformity that is independent of the thoracic diameters.