| Spinal fusion is commonly used in the treatment of lower back pain. However, an accurate technique for measuring spinal fusion in vivo has yet to be perfected. Current research on an implantable strain sensor is underway. The strains on a stainless steel vertical rod used in pedicle screw fixation were measured throughout various phases of posterolateral spinal fusion of the L4 and L5 vertebrae. The strains on the rod will be used as a criterion in the selection of an implantable sensor.; Working with cadaver spines increases the risk of contamination of equipment and personnel, in addition to requiring a lengthy period of preparation prior to testing. A synthetic discectomy model of the L4–L5 spinal unit was shown to be a safe and accurate alternative to cadaver experimentation. The difference in strain between the cadaver and discectomy model was 16 μϵ for the discectomy state, 3 μϵ for the lightly fused condition, 10 μϵ for the medium fused state, and 7μϵ for the fused condition. Additional computer simulation of the discectomy model further proved model validity for strain measurements. The difference in strain between the cadaver experimentation and simulated fusion was 3 μϵ for the discectomy state, 9 μϵ for the lightly fused condition, 19 μϵ for medium fusion, and 13 μϵ for the fused state.; Finite element analysis of a displacement sensor currently under evaluation was performed. The analysis was shown to be an accurate method of sensor displacement simulation. The finite element model is recommended to evaluate future sensors in conjunction with discectomy model experimentation. |
