How do degenerative arthritis and spinal stenosis contribute to radiculopathy?

Mechanisms of Radiculopathy in Degenerative Arthritis and Spinal Stenosis

Degenerative arthritis and spinal stenosis cause radiculopathy primarily through mechanical nerve root compression from hypertrophic facet and uncovertebral joint changes that narrow the neural foramina, combined with disc bulging or herniation and ligamentum flavum thickening that compress nerve roots in the lateral recess and central canal. 1

Primary Compressive Mechanisms

Foraminal Stenosis from Joint Hypertrophy

• Facet joint arthropathy creates bony overgrowth that directly narrows the neural foramen where nerve roots exit the spinal canal 1
• Uncovertebral joint hypertrophy (in the cervical spine) similarly reduces foraminal dimensions and compresses exiting nerve roots 1
• These arthritic changes are the dominant cause of foraminal and extraforaminal stenosis, particularly affecting upper lumbar nerve roots (L3, L4) on the concave side of degenerative curves 2

Lateral Recess Stenosis

• Hypertrophic facet joints extend medially into the lateral recess, compressing nerve roots before they exit the foramen 2
• This mechanism more commonly affects lower lumbar nerve roots (L5, S1), particularly on the convex side of degenerative scoliotic curves 2
• The subarticular zone becomes critically narrowed as degenerative changes progress 3

Central Canal Stenosis

• Ligamentum flavum hypertrophy and ossification reduces the anteroposterior diameter of the spinal canal, particularly in the thoracic spine 1
• Combined with posterior disc bulging and facet hypertrophy, this creates circumferential narrowing that can compress multiple nerve roots or the cauda equina 4
• In severe cases, this leads to neurogenic claudication rather than isolated radiculopathy 5

Disc-Related Contributions

Degenerative Disc Disease

• Disc height loss from degeneration reduces foraminal height vertically, compounding the horizontal narrowing from facet arthropathy 1
• Disc bulging associated with degenerative spondylosis contributes to lateral recess and foraminal stenosis 1
• Disc herniation superimposed on pre-existing stenosis creates acute-on-chronic nerve root compression 1

Instability and Dynamic Compression

Degenerative Spondylolisthesis

• Facet arthropathy leads to loss of posterior column stability, allowing vertebral slippage that dynamically narrows the foramen and lateral recess 5
• This creates a "double crush" phenomenon where nerve roots are compressed both by static stenosis and dynamic instability 5
• The L4-L5 level is most commonly affected by this mechanism 2

Location-Specific Patterns

Cervical Spine

• Radiculopathy results predominantly from uncovertebral and facet joint hypertrophy narrowing the neural foramina 1
• The C6 and C7 nerve roots are most frequently affected 1
• Degenerative changes correlate poorly with symptoms in patients over 30 years of age, creating diagnostic challenges 1

Lumbar Spine

• L4 and L5 nerve roots are most commonly affected overall (68% and 55% respectively in degenerative scoliosis) 2
• L3 radiculopathy is characteristic of foraminal/extraforaminal stenosis in elderly patients (average age 76 years) and often presents atypically as hip or knee pain 6
• In degenerative scoliosis, upper nerve roots (L3, L4) are compressed by foraminal stenosis on the concave side, while lower roots (L5, S1) are affected by lateral recess stenosis on the convex side 2

Thoracic Spine

• Radiculopathy is less common but results from facet arthropathy, ligamentum flavum ossification, and disc herniations (often calcified) 1
• Thoracic stenosis more commonly causes myelopathy than isolated radiculopathy 1

Clinical Implications and Pitfalls

Diagnostic Considerations

• Imaging findings correlate poorly with symptoms in degenerative disease, with high rates of false-positive findings in asymptomatic individuals over 30 years 1
• Physical examination has limited correlation with MRI evidence of nerve root compression in cervical radiculopathy 1
• In elderly patients with hip or knee pain unresponsive to joint-directed treatment, consider L3 radiculopathy from foraminal stenosis 6

Natural History

• Most cases of acute radiculopathy from degenerative stenosis resolve spontaneously or with conservative treatment 1
• The compressive mechanism is typically chronic and progressive rather than acute 4
• Factors associated with poor prognosis include older age, female gender, and coexisting psychosocial pathology 1

Treatment Implications

• Decompression alone is appropriate for stenosis without instability 5
• Fusion should be added when degenerative spondylolisthesis or documented instability is present, as decompression alone risks progression of deformity 5
• The specific compressive mechanism (foraminal vs. lateral recess vs. central) should guide the surgical approach 2