The disc joint is a cartilaginous joint that is composed of outer fibers called the annulus fibrosus that encircle the inner nucleus pulposus.
Motions of the Joints of the Lumbar Spine
Motions of the lumbar spine: The lumbar spine can move axially and nonaxially in all three cardinal planes (sagittal, frontal, and transverse).
Psoas Major Function: Spinal Joint Actions – Frontal and Transverse Planes
The frontal plane spinal action of the psoas major is fairly clear; it crosses the spinal joints laterally, so it lateral flexes the spine to that side.
