Spine disorders, primarily caused by degenerative spine conditions, deformity, tumors, and trauma, affect approximately half of the population aged over 40. To address these disorders, over 457,000 spine fusions were performed in the US in 2011 (6% annual growth), including about 290,000 anterior cervical discectomy and fusions (ACDF). ACDF surgery removes 1-4 intervertebral discs and replaces them with interbody spacers filled with bone graft. This distracts and decompress the nerve roots while fusing the adjacent vertebrae. Postoperatively, it is critical to recognize when the vertebrae have fused, an outcome that determines safe return to activity; conversely, delayed fusion may indicate need for additional interventions (e.g., prolonged collar usage, modified physical therapy, electrical stimulation, and injections such as rhPTH). Improper management can lead to poor outcomes, worse pain, surgical revision and neurological deficits. Unfortunately, patients heal at rates that vary greatly, and some patients will not heal properly with 7% needing costly revision surgery ($123,000 hospital charges). We propose to develop an X-ray Visible Interbody Spacer Indicating Biomechanical Load (X-VISIBL) fusion device to assist clinicians in tracking and detecting bony fusion. If successful, this project will validate a simple indicator that reports load on the device to assess fusion of the adjacent bones. Measurements are made using flexion/extension radiography which is already routinely used in patient follow-up but is currently insufficiently sensitive to detect delayed fusion and non-union. Monitoring implant load will provide the patient and medical team critical information to select early targeted interventions including prolonged brace or collar usage, modified physical therapy and return-to-work protocols, ultrasound or electrical stimulation, medications or injections such as rhPTH, and inform long term care to avoid device failure and associated pain, disability and reoperations. This Phase I Small Business Technology Transfer project aims to assess technical feasibility for a load indicating cervical interbody spacer. The approach is innovative in providing a sensor to clearly measure load during fusion with X-ray readout that is already part of the standard of care. To show feasibility, we must develop prototypes with mechanical properties that allow/encourage fusion (especially stiffness and yield) and the precision to detect physiological load changes during fusion. This will be accomplished with computer simulations, mechanical prototype fabrication and testing, and radiography in cadaveric models. The research is relevant to public health because, it provides an objective non-invasive means to assess biomechanical fusion and assist physicians prescribing rehabilitation protocols and adjunctive therapies.
This research project develops a first-in-kind load-indicating vertebral interbody spacer that enables physicians to track fusion status using routine flexion/extension radiography. The research is relevant to public health because it provides objective metrics to assess fusion in individual patients to inform decisions on rehabilitation protocols and adjunctive therapies.
