Measurement point: fourth intercostal space; level of the nipples in males
Measurement tool: calipers
Measurement state: at rest and standing
Parameters:
(1) coronal diameter of the thorax from left to right midaxillary line in cm (not the surface distance)
(2) anteroposterior diameter of the thorax in the sagittal plane from the midline sternum to midline spine in cm
thoracic index =
= (anteroposterior diameter) / (coronal diameter) * 100
Interpretation:
• The index is close to 100 at birth.
• From age 3 to 15 the mean value is from 73 to 75. From age 3 to 15 an index > 85 or < 63 is abnormal.
Limitations:
• The index is affected by pectus disorders (excavatum or carinatum), abnormalities of the chest cage and abnormal spinal curvature.
• Muscular development may affect the coronal measurements but should not affect the sagittal measurement. Hypotonia can decrease the sagittal measurement.
