Artificial disc replacement and intervertebral fusion devices are alternatives to pain and spinal instability when disc failure occurs. Understanding the mechanical performance of these devices can be achieved by long term clinical studies, costly experimental studies or through numeral analysis using finite elements. This study was conducted to study the subsidence, or vertical motion of the artificial disc or fusion device into adjacent vertebral body segments. Specifically, the effect of implant size, shape and sagittal profile was studied using a finite element model of the L4/L5 human spine using ABAQUS finite element software. Results compared the stress state and subsidence across spinal implant design parameters investigated.