Widening indications for spinal surgery in the osteoporotic population

Subsidence is a major complication associated with implantable devices currently used for total disc replacement and interbody fusion. These innovative implants are placed within the intervertebral spaces of the spinal column, an area that holds major weight-bearing responsibility. The subsidence event arises through a combination of poor structural support offered by the underlying bone and inadequate device design, resulting in the implant sinking through the vertebral endplates. This ultimately leads to a decrease in distance between the two vertebral bodies, thereby, reducing the intervertebral foramen, causing both nerve entrapment and radicular pain. Consequently, patients suffering from bone weakening diseases, such as osteoporosis, are currently contraindicated for these life improving procedures. This project aimed to provide the underpinning basic science on which to widen surgical indications for the elderly population, a growing demographic of patients that would most benefit from spinal interbody surgery. The first phase developed an in vitro subsidence model validated within a retrospective total disc replacement radiograph study, which ultimately recreated clinically relevant failure patterns. Prophylactic vertebral body cement augmentation is a potential method for inhibiting implant subsidence and was shown to significantly increase subsidence resistance when statically loaded with a total disc replacement shaped indenter. A 20% polymethylmethacrylate cement fill produced the greatest mechanical resistance but required an evenly distributed fill within the vertebral body to maintain the resistance across the end plate. Cyclic loading of total disc replacement implanted spinal motion segments only showed significant reduction in subsidence when the vertebrae above and below the implant were augmented with cement. Implant fixation between spiked and keel designs did not affect subsidence in cement augmented vertebrae. Finally, cement augmentation demonstrated significantly reduced subsidence in interbody fusion devices with both polymethylmethacrylate and calcium phosphate cements demonstrating similar levels of subsidence resistance. The culmination of this project provides guidelines for the effective use of prophylactic cement augmentation as a method for reducing interbody device subsidence in osteoporotic patients.EThOS - Electronic Theses Online ServiceGBUnited Kingdo