Analysis and design of an adjustable bone plate for mandibular fracture fixation

Abstract

This thesis presents the design, analysis and testing of a bone plate for mandibular fracture fixation. Conventional bone plates are commonly used to set fractures of the mandible in a surgical setting. If proper alignment between the two bone segments is not achieved, then a malocclusion can result; this condition often causes significant discomfort to the patient, and may require costly and risky revision surgery to repair. Current methods of bone plate fixation require a surgeon to visually align the segments of bone, and once the plate has been affixed to the bone, there is little that can be done to adjust alignment of the fracture. The modified bone plate presented here has a deformable mid-section, with the purpose of allowing a surgeon to compensate for mis-alignment observed after the plate has been affixed to the fractured bone. The mechanics of deformation associated with various adjustment mechanisms was explored analytically, numerically, and experimentally. It was found that in order to plastically deform the adjustable section, a force of 358.8 N is required, compared with a predicted value of 351 N obtained using numerical simulations and 487 N using a fixed-fixed beam model with a concentrated central load. In addition to static tests, a dynamic testing jig has been designed with the intent of evaluating in vitro performance of the modified bone plate. Current ASTM and ISO standards for bone plate testing require forces to be applied to the faces of the bone plate, orthogonal to the direction of loading experienced in vivo. This condition is applicable to long bones such as the humerus or femur, however loading conditions of the mandible are significantly different. The testing jig allows for any bone plate of any shape to be fixed such that a force can be applied in order to simulate the normal in vivo loading conditions. This system could be used to further optimize the design of current and future deformable bone plates before they are incorporated into invasive animal or clinical trials.