Carpal height
Carpal height is used to diagnose and assess the severity of carpal collapse. It is defined as the distance between the base of third metacarpal and the subchondral bony cortex of the distal radius. But due to variations between individuals, it is more appropriate to calculate the carpal height ratio.
Measurement
On a neutral PA radiograph of the wrist, two methods can be used to determine the carpal height ratio:
Method of Youm
It is calculated by dividing the carpal height by the length of the third metacarpal 1.
Its normal range is between 0.51 and 0.57.
Method of Natrass
This method can be used when the radiograph does not fully include the third metacarpal.
It is calculated by dividing carpal height (measured in line with the third metacarpal axis) by the greatest length of the capitate 2.
The capitate length is measured from the subchondral cortex adjacent to the bases of the second and third metacarpal to the proximal cortex along a line that passes through the center of the capitate.
Normal range: 1.57 ±0.05 3
Interpretation
These ratios change in diseases that cause carpal collapse, such as rheumatoid arthritis, Kienböck disease, traumatic injuries, and scapholunate advanced collapse
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