Ligamenta Flava (Yellow Ligaments)
Ligamenta flava (from Latin flavus – yellow) are paired elastic joints connecting the arches of vertebrae from C2 to the S1. The yellow color is due to the very high content of the elastin (highest percentage of elastic fibers of any tissue in the body1), which brings rubber-like physical properties to the joint. It is believed that this is necessary to minimize the prolapse of yellow ligaments into the spinal canal during spine extension2 and, therefore, avoid the risk of the compression of spinal structures (spinal cord and roots of the spinal nerves) caused by the narrowing of the spinal canal.
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Please note the lack of this ligament between the first two cervical vertebrae that is essential to avoid the limitation of mobility of the atlantoaxial joint. The size of the ligament isn't equal at all levels. The height and width, and thickness of yellow ligaments increase gradually from the cervical to the lumbar direction*.
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To see the anterior surface of yellow ligaments, the vertebral arches should be separated from vertebral bodies. In this illustration, you see the "anatomical" approach – the cut is done through the peduncles of vertebrae. In clinics, a section like that isn't reasonable because of the high risk of damage of spinal nerves passing via intervertebral foramina. If there is a need to open the spinal canal, neurosurgeons perform laminectomy – the cut done through the vertebral arches between the spinous and transverse processes.
Click an image to see the intact spine with yellow ligaments. Please note that the yellow ligaments extend laterally up to the intervertebral foramen1 in the thoracic and lumbar parts of the spine. Thickening of yellow ligaments coupled with disc degeneration may narrow the intervertebral opening and lead to the compression of the spinal nerve's root2,3.
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The yellow ligaments are paired joints separated from each other in a midline by the gap or groove filled with epidural fat. The arrangement of these ligaments along the posterior wall of the spinal canal changes gradually: from the more rounded in the cervical part to the more angulated and tent-like – in the lumbar1. In the cervical portion, the yellow ligaments laterally border with the zygapophyseal joints. At the same time, in the lumbar – ligamenta flava extend up to the intervertebral foramina, completely separating the joint's capsule from the spinal canal2.
Click an image to hide yellow ligaments. Please note the pattern of attachment of these joints to the vertebral arches. The upper attachment zone for each yellow ligament includes the broad area on the upper vertebral arch facing the spinal canal. In contrast, the lower attachment zone is arranged mainly along the upper edge and the posterior surface of the lower vertebra's arch3.