In Part 1 of this Masterclass on the Lumbar Spine we talked about the bones. In the last episode of The Lumbar Spine Masterclass we dissected the lumbar disc. This post we are going to talk about what holds the vertebrae and discs together... the Ligaments!!
Taken from: https://www.physio-pedia.com
Ligaments are bands of type 1 collagen that attach from bone-to-bone. They are like little pieces of rope, the do not contract like muscles, they only hold everything in place. Let’s chat about all the different ligaments in the lumbar spine, where they are, what they do and how the help to protect the spine.
Taken from: https://www.earthslab.com
The anterior longitudinal ligament, ALL, runs down the anterior aspect of the vertebral bodies. The ALL helps to limit movement when the spine bends backwards, extension. It also helps to limit anterior and posterior translation, frontwards and backwards sliding of the vertebrae on one another. The ALL has many different layers of fibres. The short fibres go from one vertebrae to the next, while the long fibres can span up to 5 vertebrae. The ALL is loosely attached to the anterior aspect of the annulus and the rims of the vertebral body. Between the ALL and the vertebral body are where the nerves and blood vessels to the vertebral body are kept.
The annulus fibrosis. As mentioned above, the annulus is outer aspect of the disc. The annulus helps to limit bending, twisting, shearing and distraction between the vertebral bodies.
Taken from: https://en.wikipedia.org
The posterior longitudinal ligament, PLL, runs down the posterior aspect of the vertebral bodies, in the spinal canal. The PLL helps to limit the amount of flexion and distraction that occurs with the vertebrae. Just like the ALL, the PLL, has deep and superficial fibres. The deep fibres span 2 vertebrae, while the superficial fibres span upto 5 vertebrae. One unique feature of the PLL is its shape. It is a saw tooth like shape. It is narrow over the posterior aspect of the vertebrae but becomes wider over the posterolateral aspect of the disc. It helps to try and reinforce the weakest part of the annulus.
Just across the spinal canal, facing anteriorly, is the ligamentum flavum. The ligamentum flavum runs along the back, posterior, aspect of the spinal canal.
It is the front, anterior, aspect of the z joint capsule. The z joint capsule holds the synovial fluid in the joint to keep the joints lubricated. The ligamentum flavum has a unique property. It is made up of elastin, 80%. This means that the ligament is elastic. This ligament attaches the lamina of the vertebrae above to the lamina of the vertebrae below. The ligamentum flavum helps to limit z joint flexion. However, when the spine extends, bends backwards, because the ligament is elastic is gets smaller and does not fold into the spinal canal. This narrowing of the spinal canal would happen if the ligament was not elastic. That is so awesome the way the body was created! I really enjoy it when the anatomy of the body just makes sense.
Moving onto the intertransverse ligaments. These guys attach the transverse process’ of the vertebrae above and below. There are two layers of intertransverse ligaments, a dorsal and ventral, back and front. Between these layers are filled with fatty tissue, nerves and blood vessels. This ligaments could help to limit the amount of rotation and side flexion that occur.
Moving posteriorly, there is the interspinous ligaments. These run from the spinous process of the vertebrae below to the spinous process above. There are three different layers, anterior, middle and dorsal fibres. Even though these ligaments are very close to the near perfect orientation to limit flexion, they do not seem to offer much resistance to separation of the spinous process’.
Taken from: https://www.semanticscholar.org
Second to last ligament is the supraspinous ligament. This runs down the back aspect of the spine, going from spinous process to spinous process. This vertebra consists of superficial, middle and deep fibres. This ligament is unusual in the fact that it does not travel the entire length of the spine. The supraspinous ligament usually ends at L4-5. This leaves L5-S1 without a ligament to pull it posteriorly… or does it?
Taken from: https://www.pdtrusa.com
The last ligament that we are going to chat about only occurs at the L5-S1 level. Although, I do hear that sometimes, the iliolumbar ligament does extend to the L4 vertebrae as well. So we are going to chat about this iliolumbar ligament. This is a very large ligament with 5 different bands, anterior, superior, posterior, inferior and vertical. It basically locks the L5 vertebrae onto the pelvis, ilium. A couple of the bands attach where the quadratus lumborum muscle attaches on the ilium. I wonder if that give this ligament a little bit of an active component, if the quadratus lumborum is activated, it pulls on the ligament tightening it up to add more support?