Morphological characteristics of spiral tibial shaft fractures involving the distal articular surface: a retrospective observational study.

Spiral fractures of the tibial shaft are frequently accompanied by injuries involving the distal articular surface; however, comprehensive investigations into the morphological characteristics of fracture lines extending to the joint surface remain limited. Existing classification systems are insufficient to comprehensively characterize the continuum of injuries spanning from the diaphysis to the articular surface. This study aimed to delineate the extension patterns of spiral tibial shaft fractures toward the distal articular surface, quantify the frequency of involvement across distinct anatomical regions, and characterize their spatial distribution, thereby providing a morphological basis for more precise diagnosis and treatment. A single-center retrospective cohort comprising 160 patients with spiral tibial shaft fractures treated at the Xi'an Jiaotong University Affiliated Honghui Hospital between May 2020 and December 2024 was included. Computed tomography (CT) images were independently screened and assessed by three senior physicians blinded to clinical data, with AO/OTA classification demonstrating excellent inter-rater reliability (κ > 0.80). Among these, 117 cases exhibited involvement of the distal articular surface. Fracture lines were registered onto a standardized tibial template utilizing a processing pipeline integrating Mimics, 3-Matic, NX, AutoCAD, and Origin software, enabling the generation of three-dimensional fracture line distribution maps and heatmaps. Among the 160 cases of spiral tibial shaft fractures, 117 (73.1%) exhibited fracture lines involving the distal articular surface. The specific distribution was as follows: 85 cases (72.6%) involved the posterior malleolus, 46 cases (39.3%) the anterior malleolus, and 29 cases (24.9%) the medial malleolus. Distribution maps revealed that 57 cases (48.7%) involved only the posterior malleolus, 16 cases (13.7%) only the anterior malleolus, and 9 cases (7.7%) only the medial malleolus; 15 cases (12.8%) involved both the posterior and anterior malleoli, 5 cases (4.3%) both the posterior and medial malleoli, and 7 cases (6.0%) both the anterior and medial malleoli. In comparison, 8 cases (6.8%) exhibited involvement of all three regions. Heatmap analysis revealed a highly modular distribution of fracture lines across the distal articular surface. The highest density was observed in the posterior malleolar region, forming an arc-shaped high-density zone. In the anterior malleolar region, two linear high-density bands were primarily located along the margins of the anterior malleolar module and the Chaput tubercle. Fracture lines in the medial malleolus were predominantly concentrated at the junction between the medial malleolar prominence and the articular surface. Spiral tibial shaft fractures frequently extend into the distal articular surface, exhibiting diverse injury patterns that go beyond the traditionally recognized posterior malleolar involvement. Notably, anterior malleolar fractures have been consistently underestimated. Existing classification systems fail to adequately capture the continuity of injuries spanning from the diaphysis to the articular surface. The fracture line distribution maps and heatmaps presented in this study illustrate a modular, region-specific pattern across the distal articular surface. These visualizations provide a foundational framework for developing an integrated classification system encompassing both the tibial shaft and ankle joint, thereby informing more refined surgical strategies and improving treatment outcomes and safety.