How Should the Shape of the Volar Rim Be Taken into Account in the Treatment of Distal Radius Fractures? A Radiological Study

Abstract In the management of articular distal radius fractures, achieving an accurate reduction of joint fragments is essential for a favorable prognosis. Fixation of the volar rim remains a surgical challenge, as volar plates may be improperly positioned despite adequate joint reduction. This study aims to analyze anatomical variations in the distal radius, focusing on the distance between the watershed line (WL) and the radiocarpal articular surface. These anatomical variations may partially explain the difficulty in achieving optimal plate placement during distal radius fracture fixation. We conducted a single-center study between October 2023 and May 2024, collecting three key measurements from computed tomography scans (CT scans) of healthy wrists. Based on distribution and correlation analyses, the wrists were categorized into two groups according to the distance from the most palmar point of the WL to the joint margin (SFWL). Group 1 included wrists with an SFWL ≥ 2.5 mm, and group 2 included those with an SFWL < 2.5 mm. The 2.5 mm threshold was selected based on the diameter of commonly used distal radius screws. This analysis revealed two emerging anatomical patterns. Then, four operators independently classified the CT scans as type 1 or 2 distal radius anatomy. Interoperators' variability was assessed using Cochran's Q test and Fleiss's kappa. A total of 100 wrists from 100 patients were included. Eighty-nine patients (89%) were classified in group 1 (SFWL ≥ 2.5 mm), and 11 (11%) in group 2 (SFWL < 2.5 mm). In group 1, three patients (3.4%) showed a negative or zero value in the minimal distance from the WL (MDFWL) to the articular surface, indicating a high risk of intra-articular screw penetration. This risk was notably higher in group 2, with three patients (27.3%) exhibiting similar findings. Interoperator variability was strong, with a Fleiss's kappa of 0.73. Our findings suggest that the distal radius exhibits a spectrum of anatomical variation, which may contribute to suboptimal volar plate placement in some distal radius fractures. Recognizing these variations preoperatively may improve implant selection and reduce the risk of flexor tendon complications. Level IIIA.