Anterior longitudinal ligament and hyperextension
The anterior longitudinal ligament lies along the front of the vertebral bodies (the weight-bearing blocks of each vertebra) and prevents hyperextension (bending the spine backwards beyond the normal range).
Remember
The anterior longitudinal ligament lies on the front of the vertebral bodies, so it is the one pulled tight when the spine bends backwards. Its weaker partner behind mainly prevents hyperflexion (bending too far forwards).
Extension is the spine bending backwards, an arching of the back, and hyperextension is going past the normal range. During that movement the front of the column is stretched, so a ligament lying there is pulled tight and checks the movement.
That ligament is the anterior longitudinal ligament. It is a thick band that runs down the front of the vertebral bodies and over the intervertebral discs (the cushions between the vertebrae). Its partner, the posterior longitudinal ligament, runs along the back of the vertebral bodies. This partner ligament is weaker than the anterior ligament, and it mainly prevents hyperflexion (bending too far forwards).
The remaining ligaments, those other than the anterior and posterior longitudinal ligaments, belong to the vertebral arch, the bony ring at the back of each vertebra. The ligamentum flavum lies between the laminae (the flat plates of the arch). The interspinous ligaments lie between the spinous processes (the bony points you can feel down the midline of the back), and the supraspinous ligament runs along the tips of those processes. Both of these limit flexion. The intertransverse ligaments lie between the transverse processes (the bony projections that stick out sideways from each vertebra) and appear to limit rotation and lateral bending.
Key facts
- Anterior longitudinal ligament
- lies along the front of the vertebral bodies and prevents hyperextension.
- Posterior longitudinal ligament
- runs along the back of the vertebral bodies, is weaker than the anterior ligament, and mainly prevents hyperflexion.
- Hyperextension
- extension (bending the spine backwards) beyond the normal range.
- Why the front ligament
- bending backwards stretches the front of the column, so the ligament lying there is pulled tight.
- Interspinous and supraspinous ligaments
- limit flexion, and lie at the back of the column.
- Intertransverse ligaments
- appear to limit rotation and lateral bending.
Exam traps
- The posterior longitudinal ligament is the classic confusion, but it runs along the back of the vertebral bodies, is weaker than the anterior ligament, and mainly prevents hyperflexion rather than hyperextension.
- The ligamentum flavum sits at the back of the column, on the side that is compressed, not stretched, in backward bending, so it is not the main restraint against hyperextension.
- The interspinous ligaments join the spinous processes at the back of the column, so they are not placed to resist a backward-bending force. They limit flexion.
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