Congruent Weber-B ankle fractures do not alter tibiotalar contact mechanics

Current treatment strategy for managing Weber B ankle fractures is mainly governed by mortise congruency, malleolar alignment, deltoid ligament competence and fracture stability. While nonoperative treatment has yielded good functional outcomes in satisfactorily aligned stable injuries, a biomechanical rationale is not firmly established. Furthermore, current radiographic analysis is obscured by observer inaccuracy and beam rotation. This study aimed to utilize weightbearing CT and computational biomechanics to analyse 3D mortise displacement and contact mechanics in Weber-B ankle fractures and compare them with the uninjured contralateral side. 32 patients were included who sustained a Weber-B ankle fracture and underwent bilateral weightbearing CT imaging at injury. Segmentation into 3D models of bone was performed semi-automatically, and individualized cartilage layers were modeled based on a previously validated methodology. The 3D mortise congruency was evaluated by use of following parameters: alpha angle, fibular length, talocrural angle, medial gutter- and tibiofibular clear space- distance mapping. Contact mechanics were evaluated by the mean and maximum contact stress of the tibiotalar articulation. Statistical analysis revealed that there were no significant differences for all anatomical parameters. There was also no significant difference between the mean contact stress of the injured (2.10 ± 0.42 MPa) and uninjured side (2.10 ± 0.41 MPa), nor the maximum contact stress of the injured (7.67 ± 1.55 MPa) and uninjured (7.47 ± 1.67), respectively. Contact mechanics were unaffected in congruent Weber-B fractures. These findings support consideration of nonoperative management in such cases, given their presumably low risk for posttraumatic arthritic development in the long term. Level of Evidence: Level III; retrospective case-control study.