Distal radioulnar joint configurations in three-dimensional computed tomography in patients with idiopathic ulnar impaction syndrome.

We retrospectively reviewed 26 patients diagnosed with idiopathic ulnar impaction syndrome and measured the slopes of the sigmoid notch and ulnar head at their centre using their preoperative three-dimensional computed tomography. We found that the slope of the sigmoid notch and that of the ulnar head were not parallel to each other. There was a significant linear relation between the slope of the ulnar head and the changes in the closest joint space of the distal radioulnar joint at the centre of the sigmoid notch after ulnar shortening. We conclude that the slope of the ulnar head is more strongly correlated with changes in the closest joint space in the distal radioulnar joint than that of the sigmoid notch. Our findings suggest that slope of the ulnar head might be as important a predisposing factor as that of the sigmoid notch for the progression of distal radioulnar joint arthritis after ulnar-shortening osteotomy. We should consider the slopes of both the sigmoid notch and ulnar head before the osteotomy. Level of evidence: IV.