Radiographic changes in the distal ulna in non-rheumatoid patients with extensor digitorum communis ruptures

Introduction Osteoarthritis of the distal radioulnar joint (DRUJ) is relatively common in elderly people. Extensor digitorum communis (EDC) ruptures occasionally and occurs with or without prior signs in these people. The purpose of this study was to clarify the radiographic changes in the distal ulna associated with EDC rupture. Materials and methods We analyzed plain radiographs of 71 patients with non-rheumatoid arthritis and 40 controls. Radiographic changes in the distal ulna were categorized into normal, osteoarthritic-change (OA-change), and taper. We measured the ulnar variance (UV) and ulnar bowing angle in the posteroanterior radiographs and the dorsal bowing angle (DBA) and dorsal protrusion (DP) in the lateral radiographs. The shape of the sigmoid notch (SN) was categorized into flat, radial inclination, and dimple. The primary outcome was a comparison of radiographic parameters between the patient and the control groups. The secondary outcome was an analysis of the type of SN to investigate factors affecting ulnar deformation. Results The ratio of the radiographic change in the ulna, UV, DBA, and DP was significantly larger in the patient group than in the control group. Patients with the radial inclination type of SN showed a greater UV than those with the dimple type. Conclusions Deformation of the distal ulna, a large UV, dorsal penetration, and dorsal bowing was related to EDC rupture. Regarding the large UV, the lunate shaved the upper half of the distal ulna, whereas the DRUJ shaved the lower half. These processes formed a tapered ulna head. A large UV and an inclination of the DRUJ played a role in ulnar head deformation.