Delta external fixation as a suitable option for definitive fixation of osteoporotic pilon fractures in biomechanics: a finite element analysis

Introduction: Pilon fractures are high-energy traumatic injuries characterized by complex metaphyseal fractures that involve the distal tibial articular surface, often accompanied by severe soft tissue damage. External fixation represent a crucial treatment treatment modality, particularly for elderly patients with osteoporosis (OP). This study aimed to identify the most suitable external fixation strategy for OP-associated Pilon fractures by comparing the biomechanics of three common used external fixations strategy. Methods: A finite element model was developed to simulate Ruedi-Allgower III/AO43C Pilon fractures combined with fibular fractures. This model was used to simulate gait cycles (swing and stance phases) for analysis of the key biomechanical parameters, including maximum von Mises stress (Max_VMS) in both bony structures and external fixation, as well as micromovements of fracture fragments, distal tibial fragments, the fibula, and the tibio-talar articular surface. These analyses were performed under both normal and OP bone conditions. Results: For the same external fixation and phase, the Max_VMS in bony structures was higher in normal bone than in OP bone, whereas the Max_VMS in the external fixation was significantly higher under OP conditions. Across all fixation, OP bone consistently exhibited greater fracture fragment micromovement than normal bone. Among the three fixations evaluated, the Delta external fixation showed the lowest Max_VMS on the tibio-talar articular surface (1.87 MPa in OP during the swing phase;