U01.11.011 Signs of lumbosacral radiculopathy

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Learning Objectives

  • Explain the pathophysiology of disc herniation (nucleus pulposus through annulus fibrosus).
  • Master the “N+1” Rule for posterolateral herniations in the lumbar spine.
  • Differentiate between L4, L5, and S1 radiculopathies based on motor, sensory, and reflex deficits.
  • Identify key physical exam maneuvers for nerve root tension.

1. Pathophysiology: The Posterolateral Slip

Intervertebral discs consist of a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus.

  • Mechanism: The nucleus pulposus herniates posterolaterally.
  • Why Posterolateral? The Posterior Longitudinal Ligament is much thinner than the Anterior Longitudinal Ligament, making the back side of the disc the path of least resistance.
  • The “N+1” Rule: In the lumbar spine, a posterolateral herniation typically affects the traversing nerve root (the one below the level of herniation). For example, an L4-L5 disc herniation hits the L5 nerve root.

2. Clinical Findings by Nerve Root

Nerve Root Disc Level Motor Deficit Reflex & Sensory
L4 L3–L4 Weakness of Knee Extension: Difficulty with stairs. ↓ Patellar Reflex; Sensation over the medial leg/malleolus.
L5 L4–L5 Weakness of Dorsiflexion; Difficulty Heel Walking. Sensation over the dorsal foot and webspace of the 1st/2nd toes.
S1 L5–S1 Weakness of Plantar Flexion: Difficulty with toe walking. ↓ Achilles Reflex: Sensation over the lateral foot/little toe.

3. Physical Exam: Tension Signs

These maneuvers stretch the nerve roots to see if they elicit radicular pain (pain radiating down the leg).

  • Straight Leg Raise (SLR): High sensitivity for L5/S1 herniation. Pain elicited between 30° 70°.
  • Contralateral SLR: Lifting the unaffected leg causes pain in the affected leg. This is highly specific for a disc herniation.
  • Reverse SLR (Femoral Stretch): Assesses upper lumbar roots (L2–L4). The patient is prone, and the knee is flexed while the hip is extended.

Activity:

Clinical Notes & Corrections:

  • Cauda Equina Syndrome: A surgical emergency! Look for “Saddle Anesthesia,” bowel/bladder incontinence, and severe bilateral leg weakness. This is caused by a massive central disc herniation compressing multiple roots.
  • Heel vs. Toe: Remember L5 = Heel (dorsiflexion) and S1 = Toe (plantar flexion). If they can’t stand on their tiptoes, think S1.

Activity: Radiculopathy Diagnostic Match

Memory Hooks:

L4: 4 kicks the door (Knee extension/Patellar). L5: 5 points to heaven (Dorsiflexion/Top of foot). S1: 1 stands on the Sun (Plantar flexion/Sole/Achilles).

Activity: