Spine Biomechanics

Strategies for the biological repair of intervertebral discs derive from the premise that disc degeneration results from impaired cellular activity and, therefore, that these structures can be induced to regenerate by implanting active cells or providing factors that restore normal cellular activity. Although in vitro organ culture studies have had some success, most studies showed a significantly decrease in cell viability with culture duration. The decrease in cell viability may be associated with a hampered fluid inflow through the endplates in vitro.

The degeneration of the intervertebral disc and the facet joints is one major reason for specific low back pain which can be induced, among other factors, by inappropriate mechanical stresses and overloading. It is still a matter of debate which structure is affected first by degenerative processes and whether a correlation exists between both.

The degeneration of the intervertebral disc is one of the most common causes of specific lower back pain. Due to multiple reasons, degeneration can lead to segmental instability. Anterior inter-corporeal spinal fusion is currently the most effective surgical treatment to correct segmental instability. In most cases, a spinal cage in combination with autogenous cancellous bone is used to achieve a permanent bony fusion of one or more vertebral segments.

Specific back pain is one of the most common causes of degenerative diseases of the lumbar spine, in the course of which there may be segment instability, facet joint arthrosis or spinal stenosis structures. Surgical therapies were designed to stabilize the segment to relieve overstressed structures and eliminate a possibly resulting narrowing of the spinal canal with compression of neural structures in the past. Today the most effective surgical treatment in segment instability is the anterior inter-corporeal fusion (spinal fusion). With autogenous cancellous bone augmented cages (spacers, cage) the therapeutically desired stabilization of the lumbar spine is brought about.

The finite element method is a very useful tool to investigate the mechanical function of biological structures. The major advantage of this method is the analysis of every possible mechanical parameter, particularly in structural regions where it may be difficult or impossible to obtain experimental data. However, model credibility must be established before clinicians and scientists can be expected to extrapolate information based on model predictions. In other words, it must be ensured that the model is verified and validated.