What is Capsular Ligaments and Ligametum Flavum?

They form thickenings of the joint capsule and very strong to spinal flexion. Fibers are shorter at the antero-lateral margins than posterior margin but they lie closer to the centre of rotation. If the vertebrae are pulled apart in a vertical direction, those two bundles fail separately, the shorter one first.

In full FLEXION these ligaments provide 39% resistance to bending and transmit an average tensile force of 591N. They offer little resistance to axial rotation,but resist hyperextension.However they resist lateral bending  / forward bending  therefore are the first structures to incur injury during excessive  movements in  antero-lateral bending.
Ligamentum flavum diagram

Ligamentum Flavum

Consists of collagen fiber namely  of elastin  – protein. Elastin gives the ligament  a yellow colour and can be stretched by 80% without failure. At 100%  stretch the ligament fails by being pulled from the bone, it also provide the spines resistance to small flexion movements. Primarily it  supplies smooth posterior lining to the vertebral foramen, which does not slack when the spine is bent backwards. That is essential anterior buckling of ligaments in this position could compromise the spinal cord.

The ligamentum flavum provides 13% of the spine residence to full flexion and its tensile strength is approximately 250 – 350 N.