Method of analysis: AP radiograph of the wrist
The original carpal height ratio ues:
(1) the length of the third metacarpal in its longitudinal midline
(2) The distance from the base of the third metacarpal to the distal cortical margin of the radius along the same line as (1)
carpal height ratio (original) =
= (distance from base of third metacarpal to radius) / (length of third metacarpal)
The disadvantage of this method is that many radiographs of the wrist do not include the entire length of the third metacarpal. To compensate for this Nattrass et al developed an modified ratio.
The modified carpal height ratio uses:
(1) The longitudinal midline of the third metacarpal.
(2) The distance from the base of the third metacarpal to the distal cortical margin of the radius along the same line as (1)
(3) The length of the capitate bone.
carpal height ratio (modified) =
= (distance from base of third metacarpal to radius) / (length of capitate)
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Method
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Reference
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original carpal height
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0.53 +/- 0.04
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modified carpal height
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1.57 +/- 0.06
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The original carpal height is approximately 0.34 of the modified carpal height.
