Kernig’s sign is a clinical indicator of meningeal irritation, elicited by resistance and pain in the hamstring muscles when the examiner attempts to extend the knee while the hip and knee are flexed at 90 degrees. Pain is usually absent when the thigh is not flexed on the abdomen.

It is commonly associated with meningitis and subarachnoid hemorrhage, but may also indicate herniated disks or spinal tumors due to nerve root compression.

Pathophysiology

• Stretching the blood- or exudate-irritated meninges surrounding spinal nerve roots produces resistance and hamstring pain.

• Sciatic pain may occur with disk herniation or spinal tumors due to direct pressure on nerve roots.

• Kernig’s sign is most reliable in adults; pediatric evaluation requires careful observation for rapid deterioration.

History & Symptom Assessment

• Determine if the patient has sudden or progressive headache, fever, nuchal rigidity, photophobia, or altered consciousness.

• Ask about back pain radiating down the legs, numbness, tingling, or weakness, history of cancer, trauma, or infection.

• Identify potential risk factors for meningitis, including recent infections, tooth abscesses, IV drug use, or exposure to endemic areas.

• Assess for risk factors for subarachnoid hemorrhage, such as hypertension, cerebral aneurysm, head trauma, or arteriovenous malformation.

Physical examination

1. Supine Position

   • Flex the patient’s hip and knee to 90°

   • Attempt to extend the knee while maintaining hip flexion

   • Resistance or hamstring pain indicates a positive Kernig’s sign

2. Neurologic Assessment

   • Evaluate motor and sensory function, reflexes, cranial nerves, and gait

   • Check for associated Brudzinski’s sign, hyperreflexia, opisthotonos, or focal neurological deficits

3. Additional Signs

   • Meningitis: fever, chills, nuchal rigidity, photophobia, seizures, cranial nerve involvement, rash (erythematous maculopapular or purpuric)

   • Subarachnoid hemorrhage: sudden severe headache, pupillary changes, decreased consciousness, focal neurological deficits, increasing ICP (bradycardia, widened pulse pressure, respiratory changes)

   • Spinal tumors/herniated disks: localized or radiating leg pain, muscle weakness, paresthesia, urinary/fecal incontinence, postural deformities

Emergency interventions

When Kernig’s Sign Signals CNS Crisis

• Immediately obtain vital signs

• Evaluate for Brudzinski’s sign

• Prepare for diagnostic imaging: CT scan, MRI, spinal X-ray, myelography

• Insert IV access and administer fluids and antibiotics if meningitis is suspected

• Provide oxygen, monitor ICP, cardiopulmonary, and neurologic status

• For subarachnoid hemorrhage, elevate the head of the bed ≥30°, darken the room, and reduce stimulation

• Ensure bed rest and minimal stress

Medical causes

1. Meningitis

   • Positive Kernig’s sign is an early feature

   • Accompanied by fever, nuchal rigidity, headache, vomiting, and possible seizures

   • Severe cases: stupor, coma, cranial nerve deficits, rash

2. Subarachnoid Hemorrhage

   • Sudden onset headache, photophobia, pupillary inequality, nuchal rigidity

   • Neurologic deficits: hemiparesis, aphasia, visual disturbances

   • Rapid progression to coma if untreated

3. Lumbosacral Herniated Disk

   • Early feature: sciatic pain

   • May have postural deformities, paresthesia, hypoactive deep tendon reflexes, dorsiflexor weakness

4. Spinal Cord Tumor

   • Pain along the affected nerve distribution

   • Weakness or paralysis distal to tumor, sensory deficits, urinary/fecal incontinence, sexual dysfunction

Special considerations

• Pediatric patients may deteriorate rapidly; Kernig’s sign is ominous in children.

• Prepare for lumbar puncture if tumor or abscess is ruled out.

• Maintain quiet environment, bed rest, and minimal stress.

Patient counseling

• Educate on recognizing meningitis signs

• Demonstrate proper use of back braces or cervical collars if needed

• Advise avoidance of activities that exacerbate disk herniation

• Discuss prevention strategies for infections

Pediatric pointers

• Rapid deterioration is possible; observe for irritability, lethargy, vomiting, or seizures

• Early intervention is crucial in children with meningeal irritation

Summary

Kernig’s sign is resistance and hamstring pain on knee extension with hip flexion, indicating meningeal irritation. Early recognition is essential to initiate life-saving interventions for meningitis or subarachnoid hemorrhage.

References

1. Dalmau, J., Lancaster, E., Martinez-Hernandez, E., Rosenfeld, M. R., & Balice-Gordon, R. (2010). Clinical experience and laboratory investigations in patients with anti-NMDAR encephalitis. Lancet Neurology, 10, 63–74.

2. Kneen, R., Jakka, S., Mithyantha, R., Riordan, A., & Solomon, T. (2010). The management of infants and children treated with acyclovir for suspected viral encephalitis. Archives of Diseases in Children, 95, 100–106.