Radiographs of the wrist often do not include the entire third
metacarpal, so the standard method for measurement of the carpal height
ratio (the carpal height divided by the length of the third metacarpal)
cannot be used. In this study, the ratio of the carpal height relative to
the length of the capitate was evaluated for its suitability as a
reproducible alternative. The revised carpal height ratio (the carpal
height divided by the capitate length) was evaluated for reproducibility
and clinical utility in both in vitro and in vivo studies: it was
determined from the radiographs of ten cadaveric wrists; those of 100
wrists (fifty pairs) of normal volunteers, made with controlled
positioning; those of 100 wrists, drawn at random from radiographs that had
been previously interpreted as showing normal findings; and those of fifty
wrists of twenty-nine patients who had documented rheumatoid arthritis. The
new ratio was found to be constant in the normal population, consistent
bilaterally, decreased in patients who had carpal collapse, and
reproducible.