Characterization of In Vivo Lumbar Range of Motion During Flexion in Healthy Subjects

The lumbar facet joint (FJ) is a unique structure located on the posterior spine. The joint is composed of two articular facets from adjacent vertebrae, which are connected by a flexible and strong facet capsular ligament (FCL) (Figure 1). Two FJs (one on each side of the spinous process) are located at every spine level and along with the IVD, create a motion segment. During spinal flexion and extension, the FCL undergoes a complex motion, with extension and shear dominating the deformation (Figure 2). The collagenous FCL guides and restricts the relative motion of adjacent vertebra in flexion.