Ligamentum Flavum Hypertrophy¶
Definition¶
Ligamentum flavum hypertrophy is the pathologic thickening of the ligamentum flavum beyond normal dimensions, resulting in narrowing of the spinal canal from the posterior direction. It is one of the most common contributors to degenerative spinal stenosis, particularly in the lumbar spine.
Pathophysiology¶
- Normal ligamentum flavum is ~80% elastin, allowing it to stretch in flexion and recoil in extension
- With aging and degeneration, elastin is replaced by collagen and fibrocartilage
- The ligament loses its ability to recoil and instead thickens and buckles into the canal, especially during extension
- Hypertrophy is accelerated by segmental instability, repetitive loading, and inflammation
Measurements¶
| Region | Normal Thickness | Hypertrophy Threshold |
|---|---|---|
| Cervical | 1.5–3.0 mm | >3.0 mm |
| Thoracic | 1.5–3.0 mm | >3.0 mm |
| Lumbar | 2.0–4.0 mm | >4.0 mm |
Imaging Findings¶
CT¶
- Thickened soft tissue density between laminae, protruding into the canal
- May show calcification or ossification (most common in the thoracic spine)
- Best measured on axial images at the facet joint level
MRI¶
- Axial T2: bilateral thickened low-signal bands compressing the posterior thecal sac
- Creates a characteristic "trefoil" or "cloverleaf" canal when combined with anterior disc bulging
- Sagittal T2: thickened ligament visible as low-signal band posterior to the thecal sac
- Dynamic component: may worsen in extension (not captured on standard supine MRI)
Clinical Pearl
Ligamentum flavum hypertrophy has a dynamic component — it buckles further into the canal during spinal extension. This means supine MRI (where the spine is in mild flexion) may underestimate the degree of stenosis that occurs during standing and walking (when the spine extends). This dynamic worsening explains why some patients have severe neurogenic claudication despite only "moderate" stenosis on supine MRI. Upright or axial-loaded MRI can capture this dynamic component.
Key Points¶
- Hypertrophy results from age-related loss of elastin and replacement with collagen
-
4 mm in the lumbar spine and >3 mm in the cervical/thoracic spine is abnormal
- A major contributor to posterior central canal stenosis
- Creates the classic "trefoil" canal shape when combined with anterior disc bulging
- Has a dynamic component — worsens in extension, underestimated on supine MRI
- Calcification/ossification is most common in the thoracic spine
References¶
- Yabe Y, Hagiwara Y, Tsuchiya M, Onoda Y, Yoshida S, Onoki T, Ishikawa K, Kurosawa D, Murakami E. Factors Associated with Thickening of the Ligamentum Flavum on Magnetic Resonance Imaging in Patients with Lumbar Spinal Canal Stenosis. Spine (Phila Pa 1976). 2022;47(14):1036-1041. PMID: 35125456. https://pubmed.ncbi.nlm.nih.gov/35125456/
- Sun C, Wang Z, Tian JW, Wang YH. Ligamentum flavum hypertrophy significantly contributes to the severity of neurogenic intermittent claudication in patients with lumbar spinal canal stenosis. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC10980470/
- Cheung PWH, Cheung JPY, Luk KDK. The paradoxical relationship between ligamentum flavum hypertrophy and developmental lumbar spinal stenosis. Scoliosis and Spinal Disorders. 2016. https://pmc.ncbi.nlm.nih.gov/articles/PMC5011336/
- Sun Y, Zhang W, Qiu Y, et al. An in vivo model of ligamentum flavum hypertrophy from early-stage inflammation to fibrosis. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC10540830/
- Gaillard F, et al. Ligamentum flavum hypertrophy. Radiopaedia. https://radiopaedia.org/articles/ligamentum-flavum-hypertrophy