Anterior Longitudinal Ligament¶
Definition¶
The anterior longitudinal ligament (ALL) is the longest and one of the strongest ligaments of the vertebral column. It runs as a continuous band along the anterior and anterolateral surfaces of the vertebral bodies from the basilar part of the occiput to the anterior surface of the sacrum.
Anatomy¶
Structure¶
The ALL consists of three layers:
- Superficial layer — spans 3–4 vertebral segments; provides long-range stability
- Intermediate layer — spans 2–3 segments
- Deep layer — bridges single adjacent vertebral bodies; firmly attached to the vertebral endplates and loosely attached over the concavity of the vertebral body
Attachments and Relations¶
- Superior: basilar part of the occiput and anterior tubercle of the atlas
- Inferior: anterior surface of the sacrum
- Width: broadest in the thoracic and lumbar regions; narrower in the cervical spine
- Relations: separated from the vertebral bodies by the basivertebral veins; blends with the anterior aspect of the annulus fibrosus at each disc level
Function¶
- Primary restraint against hyperextension of the spine
- Limits anterior disc bulging
- Provides anterior column stability
- Maintains vertebral alignment during extension
Clinical Pearl
The ALL is the primary ligament disrupted in hyperextension injuries. In elderly patients with ankylosing spondylitis or DISH, the ALL may be ossified and fractures can propagate through it like a long bone fracture, often resulting in highly unstable injuries.
Imaging Findings¶
Radiography¶
- Not directly visible on plain films
- Calcification along the anterior vertebral bodies suggests DISH when it spans ≥4 contiguous levels
- Hyperextension injuries may show widening of the anterior disc space
CT¶
- Calcification or ossification of the ALL is the hallmark of DISH — flowing calcification along the anterolateral aspect of ≥4 contiguous vertebral bodies
- Distinguished from osteophytes by the characteristic "dripping candle wax" morphology
- Best seen on sagittal reformats
MRI¶
| Finding | Appearance |
|---|---|
| Normal ALL | Thin, continuous low-signal band on sagittal T1 and T2 |
| ALL rupture | Discontinuity of the low-signal band with adjacent high T2/STIR signal |
| DISH | Thickened low-signal band with flow void artifact from calcification |
- T1-weighted sagittal images provide the best ligament-to-soft-tissue contrast for evaluating ALL continuity, because the low-signal ligament stands out against higher-signal prevertebral soft tissue and disc
- STIR outperforms standard T2 for detecting acute ALL injury — one prospective MRI/surgical correlation series reported 87.9% agreement with intraoperative findings on STIR versus 60.6% on T2, because the disc annulus and ALL are difficult to separate on T2
Key MRI Finding
In extension-distraction injuries, MRI may show disruption of the ALL and the anterior annulus with prevertebral hemorrhage with varying T1/T2 signal intensity depending on acuity and temporal evolution of hemoglobin products (typically T2 hyperintense and T1 iso to hyperintense in the hyperacute stage). Disc space widening anteriorly is a secondary sign. Reported MRI sensitivity for ALL injury is lower (~71%) than for the disc, PLL, or interspinous soft tissues — direct ligament discontinuity may be missed, so indirect signs (prevertebral edema, anterior disc gap, avulsion fragment) must be sought.
Pathogenesis note — DISH¶
Although the radiographic pattern is classically called "ossification of the anterior longitudinal ligament," cadaveric cryomacrotome work suggests the ALL itself often remains morphologically intact and is displaced anterolaterally by new bone arising from the vertebral body, rather than being directly replaced by ossification. The flowing hyperostosis is therefore best understood as paraligamentous rather than purely intraligamentous.
Key Points¶
- The ALL is the longest and one of the strongest spinal ligaments, spanning the entire vertebral column
- It is the primary restraint against hyperextension
- Ossification of the ALL defines DISH when spanning ≥4 contiguous levels
- Disruption occurs in hyperextension injuries and is best evaluated by MRI
- The ALL is firmly attached to endplates but loosely attached to the mid-vertebral body concavity
References¶
- Anterior longitudinal ligament. Radiopaedia.org. Available from: https://radiopaedia.org/articles/anterior-longitudinal-ligament
- Kuperus JS, Smit EJM, Pouran B, et al. Anterior longitudinal ligament in diffuse idiopathic skeletal hyperostosis: ossified or displaced? J Orthop Res. 2018;36(9):2491-2496.
- Murakami Y, Morino T, Hino M, Misaki H, Miura H. Progression of ossification of the anterior longitudinal ligament associated with diffuse idiopathic skeletal hyperostosis by age: a study of computed tomography findings over 5 years. Global Spine J. 2021;11(5):656-661.
- Henninger B, Kaser V, Ostermann S, et al. Cervical disc and ligamentous injury in hyperextension trauma: MRI and intraoperative correlation. J Neuroimaging. 2020;30(1):104-109.
- Li Y, Sun Y, Wu J, et al. A novel radiological scoring system for anterior longitudinal ligament injuries. Int J Gen Med. 2024;17:935-944.