Quantitative Analysis of the Volar Ulnar Corner of the Distal Radius: A Reference for Intraoperative Distal Radius Fracture Reduction

PURPOSE

The reduction of distal radius fractures using volar locking plate fixation can be performed by securing the plate to the distal fragments and then levering the plate to the radial shaft. Oblique placement of the plate on the radial shaft may lead to malreduction. The aim of this study was to evaluate parameters that can be used for the assessment of intraoperative distal radius fracture reduction using "distal-first" volar plate fixation, especially the geometry of the ulnar corner. The prevalence of Tolat distal radioulnar joint (DRUJ) types was determined, and the angles of the volar corner were quantitatively described.

METHODS

Three hundred seventy-five adult patients with a conventional wrist radiograph in their medical chart were identified. From this cohort, 50 radiographs of each Tolat DRUJ type were quantitatively analyzed using 4 angles. The probability density of each angle was described using Kernel density estimation graphs. A multivariable analysis was used to study the association between the 4 angles and Tolat DRUJ types and other patient factors.

RESULTS

One hundred fifty-one patients (40%) had a wrist with type 1 DRUJ, 147 (39%) had a wrist with type 2 DRUJ, and 77 (21%) had a wrist with type 3 DRUJ. The measurements of the distal ulnar corner, volar ulnar corner, and DRUJ angulation were significantly different among each Tolat DRUJ type. The median lunate facet inclination, relative to the axis of the radial shaft, measured 14° (interquartile range, 12°-16°) across all the Tolat DRUJ types.

CONCLUSIONS

The prevalence of Tolat type 1, 2, and 3 DRUJ was 40%, 39%, and 21%, respectively. The angles of the volar ulnar corner varied with each DRUJ type.

CLINICAL RELEVANCE

Because the lunate facet inclination was relatively consistent among all the Tolat DRUJ types, this angle may be useful as a reference for "distal-first" distal radius volar plating.

Reliability of the Sigmoid Notch Classification of the Distal Radioulnar Joint

Background  The Tolat sigmoid notch classification is a commonly used classification to characterize the distal radioulnar joint (DRUJ). This classification was based on a limited assessment of the entire joint, which may lead to inaccuracies in sigmoid notch evaluation. Questions/Purposes  The purpose of this study is to assess the reliability of the Tolat classification for sigmoid notch characterization. Methods  The sigmoid notch of 52 models of cadaveric forearms was assessed by applying the Tolat classification to the three-dimensional (3D) modeled notch and then slices at the start of the notch (0 mm) and 4 mm more proximal. The inter- and intrarater agreement was assessed using Cohen's and Fleiss' kappa statistic. Results  Agreement between iterations regardless of slices or surgeons/radiologists was moderate. Intrarater agreement between pairs of slices (0 vs 4 mm, 0 mm vs 3D, 4 mm vs 3D) was moderate, whereas agreement between all slices was slight. Agreement between surgeons and between radiologists was moderate, while agreement across all raters and slices was fair. Models described as "other" were more consistent in 3D classifications and were commonly classified as a reverse ski slope. Conclusions  Classification using the Tolat scheme is fair to moderate at best. Classification of the sigmoid notch using an axial view of the distal radius may not accurately reflect the anatomy throughout the notch. Clinical Relevance  The Tolat classification supplies a limited analysis of the sigmoid notch, and does not represent a comprehensive evaluation of the entire joint. Future classification systems should characterize the entire sigmoid notch.