Investigation of the Biomechanical Properties of Circular Frames for the Foot

Circular frames are used for the treatment of complex foot injuries, including those with bone and soft tissue loss and deformities requiring gradual correction. The most frequently used foot frame constructs are a Charcot frame, a Butt frame and a Mitre frame. The aim of this study was to provide data on the biomechanical properties of the most common configurations of foot frames in axial loading, to simulate the mechanism of loading when in use in the patient. This will provide surgeons with the necessary information to assist in selecting the most appropriate frame for a given circumstance and will facilitate further biomechanics research in this developing area. Three frame fixation model geometries were constructed using Orthofix TL-HEX components and analysed with 3 frames of each geometry constructed for a total of 9 frames. 3D foot models for use in the study were manufactured using 3D printing. The Charcot frame showed the least frame construct stiffness throughout the range of load applied with a stiffness increasing from 31 N/mm at 50N load to 93N/mm at a load of 700N, whereas the Butt frame generally produced the greatest construct stiffness increasing from 47 N/mm at 50N load to 122 N/mm at a load of 700N. The Mitre frame had the greatest initial stiffness of 53N/mm at 50N but it only increased to 105 N/mm at 700N. The Charcot frame construct presents the lowest resistance to axial loading of all the common constructs, which has implications for it’s use in patients with higher body mass index and peripheral neuropathy. The results of this study have important clinical implications, specifically with regards weightbearing instructions given to patients living with a frame.