How Intervertebral Disc Syndrome Causes Radiculopathy
Intervertebral disc syndrome causes radiculopathy through two primary mechanisms: direct mechanical compression of the nerve root by herniated disc material and chemical irritation/inflammation from leaked disc contents that excite nociceptors and damage neural tissue. 1, 2
Mechanical Compression Mechanism
Direct nerve root compression occurs when disc material herniates through the annulus fibrosus and physically impinges on the exiting nerve root in the neural foramen or spinal canal. 1
Soft disc herniation (acute disc rupture) is the most common compressive etiology, particularly at L4-L5 and L5-S1 levels in the lumbar spine and throughout the cervical spine. 1, 3
Hard disc compression results from chronic degenerative changes including osteophytes from facet or uncovertebral joint arthropathy (spondylarthrosis) that narrow the neural foramen. 1
Combined mechanisms frequently coexist, where both herniated disc material and degenerative bony changes simultaneously compress the nerve root. 1
The compression produces nerve root ischemia and mechanical deformation that disrupts normal neural conduction, leading to sensory deficits, motor weakness, and diminished reflexes in the affected dermatomal distribution. 3, 4, 2
Chemical Inflammation Mechanism
Inflammatory mediators leaked from damaged disc material play a critical role beyond simple mechanical compression. 5, 2
Herniated disc tissue releases multiple inflammatory substances including phospholipase A2, prostaglandin E2, leukotrienes, nitric oxide, and pro-inflammatory cytokines (IL-1α, IL-1β, IL-6, TNF-α). 5
These inflammatory mediators directly excite nociceptors (pain receptors), cause direct neural injury, produce nerve inflammation, and enhance sensitization to other pain-producing substances like bradykinin. 6, 5
Autoimmune reactions occur with macrophage infiltration expressing IL-1β and intercellular adhesion molecules around the herniated disc material. 5
This inflammatory response is typically most prominent in the early stages of disc herniation and tends to be transient, which explains why 75-90% of cervical radiculopathy cases resolve with conservative management. 1, 5
Clinical Manifestations
The combined mechanical and inflammatory mechanisms produce the characteristic radiculopathy syndrome:
Radiating pain extending down the limb below the knee (lumbar) or into the arm (cervical) following the specific nerve root distribution. 3, 4
Sensory changes including numbness, paresthesias, or hyperalgesia in the affected dermatome. 3, 4
Motor weakness in muscles innervated by the compressed nerve root. 3, 4
Reflex changes with diminished or absent deep tendon reflexes corresponding to the affected nerve root level. 3, 4
Important Clinical Caveats
Imaging findings do not always correlate with symptoms. Disc abnormalities are common on MRI in asymptomatic patients (20-28% prevalence), though symptomatic patients show higher rates (57-65%). 1
The size and type of disc herniation and presence of nerve root compression on imaging do not reliably predict patient outcomes. 1
MRI alone should never be used to diagnose radiculopathy and must always be interpreted in combination with clinical findings, given frequent false-positive and false-negative results. 1
Physical examination findings have limited diagnostic accuracy for cervical radiculopathy when compared to imaging or surgical reference standards. 1