Comparison of the Orientation Angles of Volar Locking Plate Distal Ulnar Locking Screw for Distal Radius Fractures.

Purpose This study aimed to measure the angles between the screw and plate in 16 commercially available volar locking plates (VLPs) to determine the fixable intra-articular fragment size. Methods Ulnar orientation angles (axial plane) and elevation angles (sagittal plane) between the distal ulnar screw and plate were measured for 14 fixed-angle VLPs and 2 variable-angle VLPs. Each VLP was simulated by 2 surgeons to sit distally and ulnarly in 10 normal distal radius models. The distance between the screw and distal/ulnar end of the distal radius on both the volar and dorsal sides, designated as the longitudinal/lateral distance, was measured to identify the fixable size of the 2 intra-articular fragments: volar lunate fragment and dorsoulnar fragment. Relationships between the ulnar orientation angle and dorsal-side lateral length as well as the elevation angle and dorsal-side longitudinal distance were analyzed. Results The ulnar orientation and elevation angles ranged from 6.5° to 16.9° and −5.8° to 34.3°, respectively, for fixed-angle VLPs and −12.5° to 32.2° and 3.1° to 42.1°, respectively, for variable-angle VLPs. The minimal longitudinal distances on the volar side with the fixed- and variable-angle VLPs were 4.3–10.9 mm and 5.8–5.9 mm, respectively. On the dorsal side, the lateral distance negatively correlated with the ulnar orientation angle (R = −0.74), and the longitudinal distance negatively correlated with the elevation angle (R = −0.89). Conclusions The Depuy Synthes variable-angle VLP provides an advantage for fixating small intra-articular fragments. For fixed-angle VLPs, the Mizuho VLP provides an advantage for fixating small volar lunate fragments. A narrow dorsoulnar fragment can be fixated using a plate with a large ulnar orientation angle, such as the Zimmer Biomet or Mizuho VLP. Clinical relevance The ability of each individual commercially available plate to capture specific intra-articular fragments should be known.