1. Introduction and methodology.

The article provides an overview of a study which describes techniques and applications when applying radiostereometry to the lumbosacral spine. Applications presented in this paper are studies of mobility in normal and degenerative lumbar segments and in spinal segments with mobility restriction by orthosis. Lumbar spine mobility happens over the disc and two facet joints on a segmental level. The radiostereometry method includes marker insertion, radiographic investigation and digitization.