A new radiographic method for evaluation of the position of the carpus in the coronal plane: results in normal subjects.

The methods used to quantify pathological variations of the position of the carpus in the coronal plane, mainly ulnar translation of the carpus from trauma or rheumatoid disease, are often difficult to use in arthritic or postsurgical wrists; moreover, they require the measurement of the whole length of the third metacarpal. The aim of this study was to determine a reliable and easy-to-use index to analyse the position of the carpus in the coronal plane. One hundred PA X-rays of normal wrists were studied, of which 56 presented with a medial hamate facet of the lunate. An index of position of the carpus in the coronal plane is defined as the ratio of orthogonal distances from [1] the most medial point of the distal radius and [2] the most medial point of the capitate to the long axis of the radius: its mean value being 1.06 (+/- 0.13) in this series of normal wrists. The index is influenced by the presence of a medial hamate facet of the lunate, but is not dependent on the ulnar head and radial styloid process, nor on the length of the third metacarpal. To help to define the usefulness of the index in quantifying the different types of ulnar carpal translations in clinical practice, further studies are required.