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Apical ligament of dens

The apical ligament of the dens is a small, thin, vertically oriented ligament located at the craniovertebral junction, connecting the tip of the odontoid process (dens) of C2 to the anterior margin of the foramen magnum. Although slender, it contributes to overall craniocervical stability by limiting excessive separation between the dens and occiput.

It is one of the midline stabilizing ligaments of the upper cervical spine, situated between the two alar ligaments and deep to the anterior atlanto-occipital membrane.

Synonyms

  • Ligamentum apicis dentis

  • Apical odontoid ligament

Location and Structure

  • Shape: Narrow, fibrous, cord-like band

  • Orientation: Vertical and midline

  • Length: Short ligament spanning from dens apex to skull base

  • Composition: Dense collagen fibers with minimal elasticity

  • Position: Deep in the craniovertebral junction, between alar ligaments and posterior to the anterior atlanto-occipital membrane

Attachments

  • Inferior attachment: Apex of the odontoid process (dens) of C2

  • Superior attachment: Anterior margin of the foramen magnum (basion region)

  • Adjacent supporting structures:

    • Alar ligaments (lateral)

    • Cruciform ligament (posterior)

    • Tectorial membrane (posterior-superior)

Relations

  • Anteriorly: Anterior atlanto-occipital membrane

  • Posteriorly: Cruciform ligament and tectorial membrane

  • Laterally: Alar ligaments

  • Superiorly: Basion region of foramen magnum

  • Inferiorly: Dens of axis (C2)

Function

  • Contributes to midline stability of craniovertebral junction

  • Helps limit excessive anterior-posterior separation between dens and occiput

  • Supports vertical alignment of occiput, atlas, and axis

  • Provides secondary restraint to excessive craniocervical movement

MRI Appearance

T1-weighted images

  • The apical ligament appears as a thin, low-signal (dark) linear band between dens and foramen magnum

  • Surrounded by intermediate-signal soft tissue and fat

  • Dens cortex: dark; marrow: bright

T2-weighted images

  • Ligament remains low signal, appearing as a dark linear structure

  • CSF around the ligament shows bright signal, enhancing contrast between structures

  • Dens shows heterogeneous intermediate-to-low signal

STIR

  • Ligament: low-to-intermediate signal, well-defined

  • Surrounding CSF: bright

  • Adjacent soft tissues remain intermediate-to-dark

T1 Fat-Saturated Post-Contrast

  • The apical ligament does not enhance

  • Fat suppression improves visualization against surrounding fat

  • Enhancing structures nearby (dura, venous plexus) provide anatomic contrast

  • Dural surfaces show mild thin enhancement, aiding boundary identification

T Appearance

Non-Contrast CT

  • The ligament itself is not directly visible due to its fine fibrous nature

MRI image

Apical ligament of dens sagittal mri image