The spine has a number of ligaments that help bind the column as a whole. These ligaments connect the individual bones together, and they help form the intervertebral joints.
Spinal ligaments also provide stability to the column. They do this by limiting the degree of movement in the direction opposite their location. For example, your anterior longitudinal ligament (see below for details) is located in front of your vertebral bodies. When you arch back, it prevents you from going too far.
Common Problems Affecting Spinal Ligaments
As we age, our ligaments may be subject to thickening, a condition called hypertrophy. Hypertrophy can cause symptoms such as nerve-related pain. Hypertrophy can develop further, into ossification, or hardening of the ligament(s). Ossification may increase the nerve symptoms, which may include compressing or otherwise irritating the spinal cord (called myelopathy). Depending on a number of factors, hardened spinal ligaments may precipitate the development of spinal stenosis.
Researchers from the Spine Clinic of the Good Samaritan Hospital in Los Angeles estimate that 25% of people with myelopathy symptoms which, as we discussed briefly above relate to the irritation or compression of the spinal cord, show signs of OPLL. (OPLL stands for ossification of the posterior longitudinal ligament. See below for more information on the posterior longitudinal ligament.)
Should you experience trauma to your spine (for example, from a whiplash), it’s possible to injure your ligaments. If the injury to your ligament(s) is severe enough, it may cause spinal instability. Instability may be defined as when the bones and ligaments comprising your intervertebral joints (also known as the vertebral segments) can no longer maintain a normal alignment when they have to bear the load. Instability can make the initial injury worse, and of course, cause pain. It may also lead to a spinal deformity. Injured ligaments that lead to spinal instability may require surgery.
Below is a list of the main ligaments that affect the movement of the vertebral column, along with their locations and their “jobs”, i.e., the direction into which limit excessive movement.
Anterior Longitudinal Ligament
The anterior longitudinal ligament is a long dense band of connective tissue—all ligaments are made of some type of connective tissue—that goes from your first vertebra (the atlas) and the front of the base of your skull to the front of your sacrum. It is located on the front side of the vertebral bodies. This ligament also branches, at each individual level, into short fibers that go between vertebrae, and insert into the front of the disc. In this way, the anterior longitudinal ligament provides support to the discs.
The anterior longitudinal ligament limits back extension, which is simply the act of arching backward. It is the only spinal ligament that limits extension.
Posterior Longitudinal Ligament
Like the anterior longitudinal ligament, the posterior longitudinal ligament starts at the base of the occiput (remember, that’s the base of your skull), and extends all the way to the sacrum. And like the anterior longitudinal ligament, the posterior branches off into short fibers that traverse the intervertebral joints, and end up, this time, at the back of the disc.
A big difference between the anterior and posterior longitudinal ligaments, and one that determines what movement direction the ligament limits, is location: The posterior longitudinal ligament (PLL) is located in the spinal canal at the back of the vertebral bodies. The anterior (ALL) is located at the front of the bodies (and not in the spinal canal). The PLL is also narrower and weaker than the ALL.
The posterior longitudinal ligament limits spinal flexion (i.e. bending forward).
The ligament flavum runs vertically from the axis vertebra (remember that’s the 2nd bone in the neck) to the sacrum. It is located between the laminae of the vertebra. At each vertebral level, fibers originate from a superior lamina (the term superior refers to a location above, relatively speaking) and connect to the inferior lamina (i.e. the lamina just below). The ligamentum flavum limits spinal flexion (bending forward), especially abrupt flexion. This function enables the ligamentum flavum to protect your discs from injury.
The phrase ligamentum flavum means "yellow ligament". The ligamentum flavum is made of a (pale) yellow-colored elastic tissue. This tissue is similar to the type of connective tissue that comprises the other spinal ligaments, except there’s a degree of elasticity to it. The elastic quality of the ligamentum flavum helps preserves your spinal curves during movement and assists the trunk in straightening up after you’ve bent forward.
Supraspinous and Interspinous Ligaments
The supraspinous and interspinous ligaments both limit flexion (forward bending).
Located in back, the supraspinous ligament is a strong rope like tissue that connects the tips of the spinous processes from your sacrum up to C7 (otherwise known as the base of the neck). Towards the neck, it merges with the ligamente nuchae.
The interspinous ligaments connect the whole of each spinous process vertically. The interspinous ligament starts at the root of the spinous process, where it emerges from the ring of bone located at the back of the body of its respective vertebra, and extends all the way out to the tip. The connective tissue that comprises the interspinous process is much weaker than that of the supraspinous.
Also known as the nuchal ligament, this ligament is located at the back of your neck. It merges with the supraspinous ligament, which as we’ve discussed, is that long, strong cord that connects the tips of most (i.e. the lumbar and thoracic) of your spinous processes.
The ligamentum nuchae go from two places on or near the back of your skull and extend through all of the cervical (neck) spinous processes.
The ligamentum nuchae are very strong. At some spots it is actually hard enough to replace bone, thereby providing attachment sites for neck muscles located in areas where the cervical spinous processes are not long enough to reach the muscle. This is the area between C3 and C5.
Intertransverse ligaments go from a superior (remember, superior refers to an above location, relatively speaking) transverse process of a vertebra to the transverse process of the vertebra below it. The intertransverse ligaments connect these processes together and help limit the action of side bending (lateral flexion). They also form a sort of border between the bodies in front and the bony rings in the back of the vertebrae.
Regarding the strength of the intertransverse ligament, in the neck, it consists of scattered fibers of connective tissue; in the low back area, it is very, very thin. In the thoracic (mid-back) area, the intertransverse ligaments are tougher and more fibrous.
Now you know your ligament ABCs. These are the spinal ligaments that affect all or at least large portions of the spine. Other spinal ligaments are specific to an area such as the neck or the sacrum and sacroiliac joints. I'll cover those in separate articles. I think the ABCs of spinal ligaments is enough to absorb in one sitting, don't you?