The biomechanical effects of bar to ring connection in a hybrid external fixator have not yet been clearly identified. The purpose of this study was to identify the biomechanical effects of bar to ring augmentation in the hybrid external fixator.

Simulated tibial plateau fractures were created using a polyvinylchloride pipe. Groups of simulated periarticular tibia fractures were stabilized with one of six different external fixation constructs with components from one manufacturer. Six frame configurations were tested: a four-ring Ilizarov frame, a hybrid frame without bar to ring augmentation, hybrid frames with three different bar to ring augmentations, a hybrid frame constructed with multiple levels of fixation in the periarticular fragment. A material testing machine was used to apply pure compression, anterior and posterior bending, medial and lateral bending, and torsion. Stiffness values were calculated from the load deformation and torque angle curves

The four-ring Ilizarov fixator was the stiffest in all modes of testing. Frame augmentation with three different types of bar-to-ring connection did increase stiffness in all modes of testing. No statistical difference was found between the stiffness of the frames with three different types of bar to ring augmentations. The stiffness of a hybrid frame constructed with multiple levels of fixation in the periarticular fragment was comparable to that of the fixators with bar to ring augmentation.

Our results show that the bar to ring augmentation increases the overall stiffness of hybrid external fixators in this periarticular tibia fracture model by 27-76%.