gms | German Medical Science

Objectives/Interrogation: Treatment of distal radioulnar joint instability remains challenging. The relative congruency of this joint depends among other structures on the morphology of the sigmoid notch. However, since the description on cadavers by Tolat and colleagues in 1996 there are very few data available on the morphology of the sigmoid notch in the transversal plane. The purpose of this study was to describe the shape and analyze variations of the transversal morphology of the sigmoid notch on axial T1-wheigted magnetic resonance imaging (MRI) sequences in healthy patients.

Methods: 88 patients with suspected scaphoid fracture which underwent MRI and standard radiographs of the wrist were included in this study. Patients with history or proved wrist instability or prior radius surgery were excluded. The sigmoid notch was analyzed on T1-weighted MRI axial plane by two readers. Its shape was categorized in four groups according to the classification of Tolat. This rather subjective classification was confronted to more objective measurements and correlated to the shape of the radius and the curvature of the ulnar head.

Results and Conclusions: The morphology of the sigmoid notch is analyzed according to the classification of Tolat. Objective measurements of the different morphology variations, as well as correlations with the shape of the ulnar head, the ulnar variance and inclination of the distal radioulnar joint are assessed. Furthermore, the presence of a distal-volar lip on the radius is discussed; it has a similar aspect to the labrum of the shoulder and seems to correspond to a broader insertion of the volar radioulnar ligament. Its relation to the shape of the sigmoid notch is also analyzed.

Transversal shape of the sigmoid notch is a potential factor influencing the stability of the distal radioulnar joint. Association with a distal-volar lip on the radius and valuable input for the surgical treatment of distal radioulnar joint instability are discussed.