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Ligamentum flavum hypertrophy refers to thickening of the ligamentum flavum, an elastic ligament that runs along the posterior margin of the spinal canal, connecting the laminae of adjacent vertebrae.

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Its hypertrophy is a key contributor to spinal canal narrowing (spinal stenosis), particularly in the lumbar spine.

Anatomy

Feature	Description
Location	Extends from C2 to sacrum; bridges laminae of adjacent vertebrae
Composition	Rich in elastic fibers (80%), yellow color due to elastin
Function	Maintains upright posture; assists in extension of spine
Pairs	Right and left sides, converging at midline posteriorly

Etiopathology

Cause/Association	Description
Age-related degeneration	Most common; due to collagen deposition and elastin loss
Mechanical stress	Chronic lumbar load and instability
Disc degeneration	Alters spinal biomechanics, increasing stress on the ligament
Facet joint arthropathy	Often co-exists; contributes to posterior canal narrowing
Obesity	Increases axial loading
Inflammatory conditions	May cause chronic ligamentous inflammation and fibrosis

Pathophysiology

Elastic tissue degeneration → fibrosis and collagen deposition
Loss of elasticity causes buckling and inward folding of the ligament during spinal extension.
Chronic inflammation may lead to ossification in some cases (seen in OLF—ossification of ligamentum flavum).

Radiology

Modality: MRI (preferred)

Measurement: >4 mm thickness at lumbar level is often considered hypertrophic (may vary with spinal level and patient age)

MRI Sequence	Imaging Finding
T1-weighted	Isointense or slightly hypointense thickened ligament posterior to thecal sac
T2-weighted	Hypointense band; may show compression of thecal sac or nerve roots
Axial view	Crucial for assessing degree of canal narrowing and nerve root impingement
Sagittal view	Shows longitudinal extent and contribution to central canal stenosis

Anatomy

Etiopathology

Pathophysiology

Radiology

Clinical Features