SCIENTIFIC ARTICLE Comparison of Plain X-Rays and Computed Tomography for Assessing Distal Radioulnar Joint Inclination Wolfgang Heiss-Dunlop, MBBS, Gregory B. Couzens, MBBS, Susan E. Peters, Karl Gadd, MBBS, Livio Di Mascio, MBBS, Mark Ross, MBBS Purpose To compare the inclination of the distal radioulnar joint (DRUJ) on computed to- mography (CT) and plain radiography (XR) in order to assess the effect of narrowing the range of inclination used in the original Tolat classification system to identify potentially problematic reverse oblique DRUJs. Methods Two independent investigators compared the angle of inclination and Tolat type on matched wrist XRs in the coronal plane and CTs of the same patients with normal DRUJs. The degree of agreement between XR and CT was determined. Inter- and intra-observer reliabilities were calculated. The prevalence of the 3 inclination types of the DRUJs using Tolat’s definition was recorded. Their original quantitative definition of the parallel Tolat type 1 DRUJ included all DRUJs with a measured inclination of 10  . We noted and compared the resultant changes in prevalence of the different DRUJ types after narrowing the inclination range to 5  and 3  . Results Highly significant correlation between CT and XR measurements were found for both observers. Despite this, the limits of agreement between CT and XR in determining the sigmoid notch inclination was e9  to 11  (2  standard deviations from the mean differ- ence). When measured from the CTs and using Tolat’s original algorithm, the prevalence of Tolat type 1 DRUJ was 47% (N ¼ 34), type 2 was 51% (N ¼ 37), and type 3 was 1% (N ¼ 1). These percentages changed to 7% (N ¼ 5) for type 1, 78% (N ¼ 56) for type 2, and 15% (N ¼ 11) for type 3 when applying narrower ranges of inclination. Conclusions Narrowing the range of sigmoid notch inclination that defines type 1 (parallel) DRUJs when using CT provided a more accurate representation of the morphological types. It revealed an increased number of potentially problematic type 3 DRUJs. However, the sta- tistical limits of agreement between CT and XR suggested that high-resolution 3-dimensional imaging is required to apply the new algorithm. (J Hand Surg Am. 2014;-(-):-e-. Copyright Ó 2014 by the American Society for Surgery of the Hand. All rights reserved.) Type of study/level of evidence Diagnostic II. Key words Computed tomograph, distal radio-ulna joint, plain radiograph, ulna shortening osteotomy. From the Department of Orthopaedics, Princess Alexandra Hospital, Brisbane, Australia; University of Queensland; Brisbane Hand and Upper Limb Research Institute, Brisbane, Australia; and the Orthopaedic Department, Barts and Royal London Hospital, London, UK. Received for publication September 26, 2009; accepted in revised form August 1, 2014. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. The authors would like to thank Irene Zeng (Biostatistician, Centre for Clinical Research and Effective Practice [CCRep], Auckland, New Zealand) and Dr Sarah L. Whitehouse (Research Fellow/Biostatistician, Institute of Health and Biomedical Innovation, Brisbane, Australia) for their invaluable assistance with the statistical analysis. Corresponding author: Mark Ross, MBBS, Brisbane Hand and Upper Limb Research Institute, Brisbane Hand and Upper Limb Clinic, 9/259 Wickham Terrace, Brisbane, 4000, Queensland, Australia; e-mail: research@upperlimb.com. 0363-5023/14/---0001$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.08.006 Ó 2014 ASSH r Published by Elsevier, Inc. All rights reserved. r 1