By Bryan J McEntire
Bryan J McEntire, chief technology officer for Amedica Corporation outlines why he believes Silicon Nitride overcomes the limitations of the materials currently used in fusion surgery.
Back pain impacts a vast percentage of the adult population today and while causes vary, the underlying issue is typically one of four spinal disorders—spondylolisthesis, scoliosis, severe disc degeneration or spinal fractures—all of which can be treated with spinal fusion surgery.
Historically, spinal surgeons used autograft and allograft bone as implant materials but have since made the shift to bioinert materials, such as metals and plastics. Two of these materials, poly-ether-ether-ketone (PEEK) and titanium, solved many of the challenges that were common with grafts, such as increased patient comorbidity, lengthy pain and healing time and disease transmission risks.
However, these materials also have limitations. They are opaque on X-rays and have less than optimal imaging characteristics with CT and MRI, which does not allow for effective assessment of fusion by clinicians. Ti implants are also prone to subsidence and therefore have essentially been replaced by PEEK.
Unfortunately, while PEEK solves some imaging and subsidence issues, the devices are known to migrate and develop pseudarthrosis , which is generally associated with the formation of a fibrous tissue layer at the implant’s surface. This fibrous layer dramatically reduces bone attachment resulting in less than optimal clinical outcomes. In addition, these two bioinert materials can also be resistant to host immune mechanisms and systemic antibiotics, creating an environment for bacterial growth. Bacterial biofilms can form on the surfaces of these devices which may induce chronic infections and reduce fusion rates. Treating implant-related infections is costly and generally requires revision surgery, resulting in extended suffering and disability for patients.
Improving Patient Care
With mounting pressure on physicians and hospitals to provide the highest possible quality of care, the need exists for a biomaterial solution for spinal and reconstructive devices that overcome the shortcomings of the commonly used materials. Silicon Nitride (Si3N4) is potentially such a material. It is a ceramic with properties that include high strength and fracture resistance. In fact, it is the most fracture resistant ceramic material commercially available.1
It also has features that make it attractive as a biomaterial. For example, it delivers good mechanical properties, superior biocompatibility, anti-infective and osteointegrative characteristics, all of which potentially result in greater clinical efficacy. It is also compatible with all imaging modalities; and promises higher wear resistance and long-term durability. Amedica is currently the only company with FDA clearance to manufacture and distribute Silicon Nitride implants. This technology is currently driving a new standard of care for patients suffering from back pain requiring spinal fusion.
Bryan J McEntire, chief technology officer, Amedica Corporation
1. Bal et al. Actobiomaterialia 2012 submitted for publication