A Stable Solution: Biomechanical Assessment of External Fixators for the Treatment of Pelvic Injury Type AO 61 C1.3a

This study aimed to analyse the load-deformation behaviour of pelves treated with external fixation following AO61C1.3a pelvic injury. Designing a biomechanical setup , the load-bearing capacity of pelves was assessed across varying pin configurations (two, three, or four external fixator pins). Mechanical parameters such as stiffness, peak-to-peak, valley-to-valley, fracture line, total displacement, deformation, and maximum load were derived to quantify pelvis stability. The 3-pin configuration demonstrated superior stability with significantly smaller pubis and sacral fracture displacements under all loading conditions (p<0.001), and was the only configuration below the clinical failure threshold. Notably, this configuration minimised fracture movement despite global outcome parameters showing no significant differences between the groups. These findings highlight the importance of fracture-specific stability over global stiffness in ensuring effective fixation. The results indicate that optimal biomechanical resistance to C1.3a pelvic instability is achieved through a combination of two pins on the injured side and a single pin on the stable hemipelvis using contemporary pin devices. This study offers the biomechanical basis required to facilitate the design and execution of clinical trials addressing pelvic ring injuries.