Development of a Novel Piezoelectric Implant to Improve the Success Rate of Spinal Fusions

Abstract

The purpose of this thesis is to design and show preliminary proof of concept for a piezoelectric fusion cage, which will help stimulate bone growth during spinal fusions. The fusion cage will utilize a novel piezoelectric composite. Back pain is one of the most common neurological diseases, second to only headaches. The primary surgical procedure to relieve lower back pain is known as a lumbar interbody fusion. The goal of this surgery is to stabilize the problematic spine segment by removing the intervertebral disc, stabilizing the segment with instrumentation, and growing bone between the vertebrae. This surgery, however, is far from perfect. Failure of the vertebrae to fuse occurs in 10 to 46% of all patients, depending on patients' inherent factors. Electrical stimulation has been found to significantly increase fusion rates, but requires extra instrumentation and is expensive. To overcome these issues, development has begun on a piezoelectric fusion cage, which will generate electricity as it is compressed between the vertebrae during normal activities. A design for the implant has been developed that is made primarily of a piezoelectric composite, but will include additional materials and circuitry. The implant will safely deliver a bone-growing, negative electric potential to the fusion, while protecting the fusion from the bone-resorbing, positive electric potential. A theoretical power analysis and material generation research were conducted simultaneously. The power analysis for piezoelectric composites was developed using a lumped parameters model based off of previous piezoceramic models. It was used to find trends in the implant parameters to help generate the appropriate amount of current density to deliver to the fusion. The material generation research was conducted to validate the results of the theoretical model. The current generated by the material followed the same trends as the theoretical model and values for theoretical maximum current were within 36% of the experimental results. Based on the results, the theoretical model should be acceptable to find trends in the current output. From these results, a composite generating the required current density should be feasible, meaning the implant could significantly increase the success rates of spinal fusions.