Lisfranc injuries affect at least 1 out of every 55,000 people each year. Although they are rare foot injuries, their effects can be devastating. 20-40% of Lisfranc injuries are missed upon first presentation. This increases the number of poor outcomes, resulting in a disproportionate number of malpractice lawsuits and compensation claims. The Kingston Brace was designed to support an injured foot during a CT scan with the goal of providing the diagnosing physician with the best diagnostic information possible. A prototype was designed and built to support a variety of foot orientations in order to determine which orientation is optimal for Lisfranc joint CT scanning. Three fresh frozen cadaver feet were put through several experiments with the Brace. The 2D diagnostic quality of CT scans taken using the Kingston Brace was compared against that of CT scans using the existing protocol. The Kingston Brace allows for a greater visualization of the injured Lisfranc joint than the existing CT protocol. Lisfranc joint spreading was used as a measure of potential pain in injured patients. The joint spreading was minimal, suggesting that injured patients would not feel as much additional pain during imaging. Also, the adoption of the Kingston Brace resulted in no change in the morphological parameters resulting from more advanced 3D analysis. The experimentally determined optimal Kingston Brace orientation was found to be 9◦ of plantarflexion and 13◦ of eversion. These orientations can be incorporated into the next generation of Kingston Brace design. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-07-06 15:01:57.866

While Lisfranc injuries in the mid foot are less common than other ankle and mid foot injuries, they pose challenges in both properly identifying them and treating them. When Lisfranc injuries are ligamentous and do not include obvious fractures, they are very challenging for clinicians to identify unless weight bearing radiographs are used. The result is that 20%-40% of Lisfranc injuries are missed in the initial evaluation. Even when injuries are correctly identified the outcomes of surgical procedures remain poor. Existing literature has compared the different surgical procedures but has not had a standard approach or procedures across studies. This study uses a computational biomechanical model validated on a cadaveric study to evaluate factors that impact injury presentation and to compare the different procedures ability to stabilize the Lisfranc joint after an injury. Using SolidWorks® a rigid body kinematic model of a healthy human foot was created whereby the 3D bony anatomy, articular contacts, and soft tissue restraints guided biomechanical function under the action of external perturbations and muscle forces. The model was validated on a cadaveric study to ensure it matched the behavior of a healthy Lisfranc joint and one with a ligamentous injury. The validated model was then extended to incorporate muscle forces and different foot orientations when simulating a weight bearing radiograph. The last section of work was to compare the stability of four different surgical repairs for Lisfranc injuries. These procedures were three open reduction and internal fixation (ORIF) procedures with different hardware (screws, screws and dorsal plates, and endobuttons) and primary arthrodesis with screws. They required use of finite element analysis which was performed in Ansys Workbench. For the presentation of injuries, both muscle forces and standing with inversion or eversion could reduce the diastasis (separation) observed for weight bearing radiographs and thus confuse the diagnosis. When comparing the different surgical procedures, the ORIF with screws and primary arthrodesis with screws showed the most stable post-operative Lisfranc joint. However, the use of cannulated screws for fixation showed regions of high stress that may be susceptible to breakage. A challenge in the literature has been the use of different experimental designs and metrics when comparing two of the possible procedures for a Lisfranc injury head to head. This study has been able to benchmark four procedures using the same model and set of metrics. Since none of the existing procedures showed consistently good to excellent patient outcomes, more procedures could be proposed in the future. If this were to occur, this study offers a standard procedure for benchmarking the new procedure’s post-operative mechanical stability versus those procedures currently in use.

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