Relevance of in vitro and in vivo models for intervertebral disc degeneration.

Models available for the study of intervertebral disc degeneration are designed to answer many important questions. In vitro biologic models employ a variety of cell, tissue, or organ culture techniques with culture conditions that partially mimic the cellular environment of the degenerated human intervertebral disc. In vitro biomechanical models include intervertebral disc or motion-segment loading experiments as well as finite element modeling techniques. The literature describes numerous in vivo animal models for use in the study of intervertebral disc degeneration, each of which has its own advantages and disadvantages. Human-subject studies have included the use of magnetic resonance imaging and other techniques to assess diffusion into the intervertebral disc, to measure intradiscal pressure, to conduct kinematic or stiffness studies of lumbar motion segments, and to evaluate muscular forces on the spine. Although all of these studies are helpful in answering specific questions, their relevance in assessing disc degeneration in patients with symptoms of discogenic pain must be carefully considered.