What is the medical term for the neurological exam where the knee is at 45 degrees, the foot is in dorsiflexion, and it causes the foot to plantar flex and extend rapidly and involuntarily?

Babinski Reflex (Babinski Sign)

The neurological exam you're describing is the Babinski reflex (also known as the Babinski sign), which is elicited when dorsiflexion of the foot causes extension of the great toe with fanning of the other toes.

Technique for Eliciting the Babinski Reflex

The Babinski reflex is properly elicited through the following procedure:

• Position the patient supine with the knee flexed at approximately 45 degrees
• Apply a firm but not painful stimulus along the lateral aspect of the sole of the foot, starting at the heel and moving forward to the base of the toes
• Observe the response of the toes, particularly the great toe

Normal vs. Abnormal Response

• Normal (negative) response: Plantar flexion of all toes
• Abnormal (positive) response: Dorsiflexion of the great toe with or without fanning of the other toes

Clinical Significance

A positive Babinski sign indicates upper motor neuron dysfunction, suggesting pathology in the corticospinal tract. This finding is:

• Normal in infants up to 12-24 months (due to incomplete myelination)
• Abnormal in adults and older children
• An important indicator of potential neurological disorders

Variations and Related Tests

Several variations of this reflex test exist:

• Chaddock sign: Stroking the lateral aspect of the foot below the lateral malleolus
• Oppenheim sign: Applying firm pressure along the anterior tibia
• Gordon sign: Squeezing the calf muscle
• Moniz sign: Forceful passive plantar flexion at the ankle with observation of great toe extension

Differential Diagnosis of a Positive Babinski Sign

A positive Babinski sign may indicate:

• Stroke
• Multiple sclerosis
• Spinal cord injury or compression
• Brain tumor
• Amyotrophic lateral sclerosis
• Traumatic brain injury
• Meningitis or encephalitis

Clinical Pearls and Pitfalls

• Ensure the patient is relaxed during testing, as voluntary movement or tension can affect results
• The stimulus should be firm but not painful enough to cause withdrawal
• A cold foot may give false results; ensure normal temperature
• Avoid testing immediately after a previous positive response, as there may be a refractory period
• Distinguish from withdrawal response, which involves flexion at multiple joints

Documentation

When documenting findings, specify:

• The exact technique used
• The observed response
• Whether the finding was bilateral or unilateral
• Any associated neurological findings

The Babinski reflex is a critical component of the comprehensive neurological examination and provides valuable information about the integrity of the central nervous system, particularly the corticospinal tracts.