Biomechanics of the human spine and trunk.

This chapter has reviewed the past 30 years of experimental biomechanical studies of the spine and trunk. In the last 10 years, computers have allowed the development of simulation techniques and models to predict spine and muscle loading in most static and quasi-static activities. Some problems remain, however, particularly with activities involving bending and twisting and those that entail maximal efforts. Current research is focused on trying to validate models for the analysis of dynamic activities involving simple planar motions. Although the body segment kinematics and external support forces in complex motions can be measured fairly easily with modern motion analysis equipment, models that correctly predict the internal trunk forces have yet to be fully developed and validated. These models will be useful in studying how, why, and where failure of the soft and bony tissues is most likely to occur in a given activity, and whether it is related to work or athletics. The challenge for the future is to develop models that adequately reflect the anatomical sophistication of the spine and trunk. Thus the stress and strain distributions in any trunk musculoskeletal component, whether the posterior wall of the annulus, a muscle slip of the semi-spinalis group, or the lumbosacral endplate, will be able to be found. These results can then be combined with models of cumulative trauma response to successfully identify potential failure sites.