Access Type

Open Access Dissertation

Date of Award

January 2018

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biomedical Engineering

First Advisor

King H. Yang

Abstract

Trauma to the pelvis is debilitating and often needs fixation intervention. In 58% of patients with this trauma, the injuries can lead to permanent disability, preventing the return to jobs. Of all unsuccessful fixation procedures, 42% are caused by failures of the method, sometimes due to mobilization during healing. The unstable anteroposterior compression fracture is of particular concern due to the blood loss into the increased pelvic volume with the pelvic ring fracture. External fixation was introduced for an expedient solution. This fixation has drawbacks such as few positions for the patient during healing and an increased chance of screw site infection. A method was developed, called INFIX, and is applied percutaneously to provide the same benefits as the external fixation method but eliminates the drawbacks.

Patients would benefit by having fixation hardware in place that enables ambulation. This would allow increased comfort and self-care. During walking, the ground reaction forces through the legs and into the pelvis can induce torsion into the pelvic ring and across the joint cartilages. An understanding of how the INFIX responds to these walking forces is needed. It is also necessary to determine the effect of the INFIX on the stability of the pelvic ring. From this, modifications can be developed that allow for ambulation. The aims of this study were to provide a method, using finite element (FE) analysis, for evaluating the intact pelvic responses under the walking conditions, to use the FE model to analyze the INFIX method during walking conditions, and to develop an improved method that would potentially allow for ambulation.

A method was developed that incorporated all of the necessary ambulation factors in four bilateral, static, FE models representing eight gait phases. For this study, an understanding of the associated anatomy was necessary. Additionally, the biomechanics of the pelvis, the fracture classifications and the related fixation methods needed to be researched. The FE models were built as static bilateral pelvic structures, including the ligaments, hip inputs, leg and trunk muscles, and hip motions. Then the anteroposterior compression fracture and INFIX hardware were applied to the gait-phase models and analyzed. Finally, an improvement method was developed and analyzed.

The resulting stress contours of the full pelvic ring, the pelvic ring and hardware deformation, and the pubic symphysis displacement were evaluated and reported under the baseline, original hardware, and improved hardware conditions.

Due to this study, the stress response of the pelvis due to walking phases is provided and adds new knowledge to the field for applying pelvic fixation methods. The INFIX method is better understood in terms of the deformation of the hardware while in place and the effect it is having on the pelvic system. Additionally, a new cross-rod configuration, the Bridge-X, was designed through numerical simulations to allow early ambulation that is needed to promote better healing. In subsequent work, additional phases of the gait can be modeled to ensure the worst case scenarios are being considered. Biomechanical testing could be used to validate the new improved method relative to the original method. This modeling method can be applied to other types of fractures and new fixation methods as they are being developed.

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