Ulnar translation of the scaphoid: an early X-ray sign of rheumatoid arthritis

Abstract

The distance between the os trapezium and radius (which we called scaphoid distance) became shorter during the course of rheumatoid arthritis (RA). Measurement of this distance was performed in 600 hands (300 patients), using standard position of patient's hand in supination with permanent angle (15-20%) between the axis of the radius and the axis of the third metacarpal bone (scaphoid distance). This provided a stable distance between the most distal point of the radial styloid process and most proximal point of the os trapezium. The patients were divided into two groups: a control group consisting of 100 patients with no inflammatory joint disease, and a group of 200 patients suffering from RA. Patients suffering from RA with bone erosions had smaller scaphoid distance than those suffering from RA without bone erosions. The ratio between the distance from the distal radius to the most distal point of the third metacarpal bone and scaphoid index was called carpo-metacarpo-scaphoid index. It excluded the constitutional influence on the scaphoid distance. The shorter the scaphoid distance, the bigger the carpo-metacarpo-scaphoid index. The average indexes were: in the control group 7.8 (+/- 0.4), in group 2A with advanced RA 21.1 (+/- 4.1), and in group 2B with early RA without bone changes 12.0 (+/- 1.6). The results were statistically significant. The measurements are easy to perform and may be helpful in the early X-ray diagnosis of RA, when there are no bone erosions, or narrowing of articular spaces.