Kinematics of the Spine Under Healthy and Degenerative Conditions: A Systematic Review.

Understanding spinal kinematics is essential, not only for the comprehension and diagnosis of spinal diseases, but also for improving modern tools and software. The sheer volume and complexity of now available information can be overwhelming. We aimed to distil it into a form that facilitates comparison among diverse studies addressing spinal kinematics under healthy and degenerative conditions. We specifically aimed to define a baseline definition of the spectrum of normal spinal kinematics that in turn allows a comparable definition of kinematics of the degenerative lumbar spine. The considered data was obtained by a systematic MEDLINE search including studies on angular/translational segmental motion contribution, range of motion, coupling and center of rotation. As for degenerative conditions, we collected publications on disc degeneration, facet joint osteoarthritis, facet joint tropism, spondylolisthesis, ligament degeneration and paraspinal muscle degeneration. While we could demonstrate repeating motion patterns for some topics, agreement in other fields is limited due to methodological variances and small sample sizes, particularly in publications with highly accurate but complex techniques. Besides, the high frequency of concurrent degenerative processes complicates the association between diseases and subsequent kinematical changes. Despite several substantial gaps, we stand at the precipice of technological breakthroughs that can power future large-scale studies.