Three-Dimensional Analysis of Polyaxial Volar Locking Plate Position for Distal Radius Fracture.

 To avoid screw penetration into the joint when using the polyaxial volar locking plate (VLP) for osteosynthesis of distal radius fractures, it is important to note that the optimal screw insertion angles depending on the plate positions.  The purpose of this study was 2-fold: first, to evaluate the differences of the most distal plate position where the screw does not penetrate into the joint in the three-dimensional (3D) radius models; second, to evaluate the relationship between the plate position and the transverse diameter of the distal radius.  Thirty plain X-rays and computed tomography (CT) scans of healthy wrists were evaluated. The transverse diameter was measured on plain X-rays. 3D radius models were reconstructed from CT data. A 3D image of polyaxial VLP was used to investigate the most distal plate position at three different screw insertion angles. The linear distance between the volar articular edge and the plate edge was measured and compared among different screw insertion angles. The correlations between the plate positions and the transverse diameter were also evaluated. In addition, the relationship between the most distal screw place and articular surface was confirmed with one case of distal radius fracture.  The optimal positions relative to the neutral were 2.7 mm proximal in the distal swing and 1.9 mm distal in the proximal swing. The linear distance was significantly correlated with the transverse diameter in each group. It was confirmed that the relationship between the most distal screw place and articular surface was applicable in the actual case.  The results showed that the most distal position of the polyaxial VLP differed depending on the screw insertion angle and became more proximal as the transverse diameter increased. These results may be useful as a reference for preoperative planning.  III.