There are many issues to consider in evaluating the biomechanics of lumbar arthroplasty, which may consist of a nucleus replacement, a total disc replacement, or a mobile posterior device. The goal of spinal arthroplasty is to replicate or augment the function of the normal spinal elements, by taking into consideration both in the quantity and quality of motion that occurs across the replaced joint. This article describes the relevant parameters for studying the biomechanics of lumbar arthroplasty and briefly summarizes the current knowledge with regard to those parameters in some well-known lumbar nucleoplasty, facet replacement, and total disc arthroplasty devices.