Physiopathology of Intervertebral Discs Flashcards
Aggrecan - Role
Most common proteoglycan in the disc. Enables tissue to support compressive load and transfer it equally.
Chondrocytes - Role
Synthesize matrix: proteoglycan and collagen.
Break down matrix: Matrix Metalloproteinase (MMP).
What happens in an injured disc?
Increase in catabolic cytokines and MMPs. Healing process overtaken by degenerative changes.
Risk Factors for Degeneration (8)
Genetic predisposition (5A,6A alleles regulate MMPs)
IVD avascular: poor transportation of nutrients.
Nutrition
Smoking
Cell senescence
Degraded matrix product
Fatigue failure of nucleus
Heavy load
Consequences of Degeneration (5)
Disc can no longer function hydrostatically under load.
Stress of load causes annular bulge.
Loss of height alters mechanics of facet joints:
- osteophytes at disc margin and facet joint margin.
- Periarticular fibrosis (ligament, capsule).
- Buckling of ligament flavum.
What does the nr. and activity of disc cells depend on?(5)
Mechanical loading, nutrient transport, life-style, genetic factors and growth factors.
Cell turnover decreases progressively with time. Also transport of nutrients (from joint end-plate to disc).
Discogenic Pain - Mechanisms (2)
Outer layers of annulus fibrosis innervated.
Arises from structural failure of the disc → abnormal motion → provokes mechanical stimuli → generates peripheral sensitisation.
Or arises from nociceptive neurotransmitters, neural and vascular ingrowth (mast cells).
Herniated Disc - Stages (4)
Bulging
Protrusion
Extrusion
Sequestration
Herniated Disc - Bulging
Extension of disc margins beyond margins of adjacent vertebral endplate. All layers still intact.
Herniated Disc - Protrusion
Posterior Longitudinal ligament (PLL) remains intact but nucleus pulposus impinges on annulus fibrosus.
Herniated Disc - Extrusion
Nuclear material emerges through annular fibers but PLL remains intact.
Herniated Disc - Sequestration
Nuclear material emerges though annular fibers and PLL is disrupted. Portion of nucleus pulposus protrudes into epidural space.
Reabsorption of Herniated Discs
67% spontaneous reabsorption. 6 months - 2 years.
Better recovery from later stages.
Spinal Stenosis - Definition
Narrowing of the spinal canal.
Mainly in cervical and lumbar spine.
Spinal Stenosis - Types (2)
Congenital: likely to have lumbar stenosis if you already have cervical.
Acquired: Degenerative arthritis, degenerative ligament flavum (leads to buckling), Spondylolisthesis (antero or retro).
