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.
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 centre of the capitate.
Normal range: 1.57 ±0.05 3
- 1. Youm Y, McMurthy RY, Flatt AE, Gillespie TE. Kinematics of the wrist. An experimental study of radial-ulnar deviation and flexion-extension. J Bone Joint Surg Am 1978;60(4):423-431.
- 2. Natrass GR. King Gj, McMurtry RY, Brant RF. An alternative method for determination of the carpal height ratio. J Bone joint Surg Am 1994;76(1 ):88-94.
- 3. Stahelin A, Pfeiffer K, Sennwald G, Segmuller G. Determining carpal collapse: an improved method. J Bone Joint Surg Am 1989; 71:1400–1405.