Ligamentum Flavum¶
Definition¶
The ligamentum flavum (Latin: "yellow ligament") is a paired elastic ligament that connects the laminae of adjacent vertebrae, forming a portion of the posterior wall of the spinal canal. Its name derives from its yellow color, which is due to its exceptionally high elastin content (~80%).
Anatomy¶
Structure¶
- Composition: approximately 80% elastin and 20% collagen — the highest elastin content of any ligament in the human body
- Orientation: extends from the anteroinferior surface of the upper lamina to the posterosuperior surface of the lower lamina
- Extent: present from C2–C3 to L5–S1; absent between the occiput and C1, and between C1 and C2 (replaced by the posterior atlanto-occipital and atlanto-axial membranes)
- Paired structure: the right and left ligamenta flava meet in the midline, sometimes with a small gap through which the epidural veins communicate
Dimensions¶
- Thickness: normally 2–4 mm; thickest in the lumbar region
- Hypertrophy: considered pathologic when >4 mm in the lumbar spine or >3 mm in the cervical spine
Function¶
- Maintains smooth curvature of the posterior spinal canal wall
- Stretches during flexion and recoils during extension without buckling
- Prevents impingement on the spinal cord and nerve roots during dynamic motion
- Assists in returning the spine to neutral position after flexion
Clinical Pearl
Ligamentum flavum hypertrophy is one of the most common causes of lumbar spinal stenosis, particularly in the lateral recess and subarticular zones. It often occurs in conjunction with facet arthropathy and disc bulging, resulting in a "triple crush" of the neural elements. The loss of elastin and replacement with collagen leads to thickening and loss of the ligament's ability to recoil, causing it to buckle into the canal during extension.
Imaging Findings¶
Radiography¶
- Not directly visualized on plain radiographs
- Calcification may occasionally be seen as a faint density overlying the posterior spinal canal
CT¶
- Normal ligamentum flavum: thin, homogeneous soft tissue density between laminae
- Hypertrophy: thickened >4 mm in the lumbar spine; appears as bilateral soft tissue thickening narrowing the spinal canal posteriorly
- Calcification/ossification: hyperdense foci within the ligament; most common in the thoracic spine
- Best evaluated on axial images at the level of the disc space and facet joints
MRI¶
| Finding | Appearance |
|---|---|
| Normal | Thin, low-signal band on T1 and T2 between laminae |
| Hypertrophy | Thickened low-signal band, >4 mm, often compressing the thecal sac |
| Cyst | Well-circumscribed T2-hyperintense lesion arising from the ligament, may mimic a synovial cyst |
| Calcification | Low signal on all sequences; confirm on CT |
Key MRI Finding
On axial MRI, the hypertrophied ligamentum flavum appears as bilateral thickened low-signal bands compressing the posterior thecal sac, creating a characteristic "trefoil" or "clover-shaped" canal on axial images when combined with a disc bulge anteriorly.
Key Points¶
- The ligamentum flavum has the highest elastin content (~80%) of any human ligament
- It connects adjacent laminae from C2–C3 to L5–S1
- Hypertrophy (>4 mm lumbar, >3 mm cervical) is a major cause of spinal stenosis
- Calcification/ossification is most common in the thoracic spine
- MRI shows hypertrophy as thickened low-signal bands compressing the thecal sac posteriorly
- Often coexists with facet arthropathy and disc bulging in degenerative stenosis
References¶
- Altinkaya N, Yildirim T, Demir S, Alkan O, Sarica FB. Factors associated with the thickness of the ligamentum flavum: is ligamentum flavum thickening due to hypertrophy or buckling? Spine (Phila Pa 1976). 2011;36(16):E1093–7.
- Kolte VS, Khambatta S, Ambiye MV. Thickness of the ligamentum flavum: correlation with age and its asymmetry—a magnetic resonance imaging study. Asian Spine J. 2015;9(2):245–253.
- Chelladurai A, Balasubramaniam S, Anbazhagan SP, Gnanasihamani S, Ramaswami S. Dorsal spinal ligamentum flavum thickening: a magnetic resonance imaging study. Asian Spine J. 2018;12(1):47–51.
- Fang N, Wang Z, Jiang J, Yang A, Mao T, Wang Z, Chen Q. Nonsurgical therapy for lumbar spinal stenosis caused by ligamentum flavum hypertrophy: a review. Medicine (Baltimore). 2024;103(27):e38782.
- Hirabayashi S. Ossification of the ligamentum flavum. Spine Surg Relat Res. 2017;1(4):158–163.
- Sairyo K, Biyani A, Goel V, et al. Pathomechanism of ligamentum flavum hypertrophy: a multidisciplinary investigation based on clinical, biomechanical, histologic, and biologic assessments. Spine (Phila Pa 1976). 2005;30(23):2649–2656.
- Ligamentum flavum hypertrophy. Radiopaedia.org. Available from: https://radiopaedia.org/articles/ligamentum-flavum-hypertrophy
- Ossification of the ligamentum flavum. Radiopaedia.org. Available from: https://radiopaedia.org/articles/ossification-of-the-ligamentum-flavum