The extensor thrust reflex is a primitive neonatal reflex characterized by extension of the leg upon stimulation of the sole of the foot. It is mediated at the spinal cord level, is normally present at birth, and typically disappears by 6 months of age.

Pathophysiology

• Neurodevelopmental basis: This reflex is mediated by spinal cord pathways without cortical modulation.

• Normal process: In neonates, the immature nervous system allows primitive reflexes to be expressed. As higher cortical centers mature, these reflexes are inhibited and disappear.

• Abnormal persistence or recurrence: Persistence beyond 6 months suggests anoxic brain damage or other neurological disorders. Recurrence in older children or adults indicates central nervous system lesions (e.g., cerebral palsy, traumatic brain injury).

Examination Technique

• Patient positioning: Place the neonate in a supine position with one leg flexed.

• Stimulation: Firmly but gently stimulate the sole of the flexed foot.

• Expected response (normal): The leg will slowly extend.

• Interpretation:

  • Present in neonates (normal).

  • Weak in premature neonates.

  • Abnormal if persistent > 6 months or reappears later in life.

Clinical Utility

• Neonatal neurology: Helps assess the integrity of spinal reflex pathways.

• Developmental monitoring: Loss at the expected age indicates normal neurological maturation.

• Pathology marker: Persistence or reappearance signals CNS injury, anoxia, or developmental abnormalities.

Differential Diagnosis of Abnormal Reflex Persistence

Pediatric Considerations

• Premature neonates may show weaker responses due to underdeveloped motor pathways.

• Monitoring disappearance is crucial in developmental surveillance.

Geriatric/Adult Considerations

• Reflex should never be present in adults.

• Reappearance strongly indicates CNS pathology, especially upper motor neuron lesions.

Limitations

• Requires proper positioning and technique.

• Reflexes may vary in premature or ill neonates.

• Should always be interpreted in conjunction with other primitive reflexes and developmental milestones.

Patient/Parent Counseling

• Explain that the reflex is normal in newborns and disappears as the nervous system matures.

• Emphasize that persistence or recurrence requires further neurological evaluation.

• Reassure that weak responses in premature infants may reflect immaturity, not always pathology.

Conclusion

The extensor thrust reflex is a primitive neonatal reflex normally disappearing by 6 months of age. Its persistence or reappearance is an important clinical marker of central nervous system dysfunction and requires thorough neurological assessment.

References

1. Volpe JJ. Neurology of the Newborn. 6th ed. Philadelphia, PA: Elsevier; 2018.

2. Rennie JM, Kendall G. Avery’s Neonatology: Pathophysiology and Management of the Newborn. 8th ed. Philadelphia, PA: Wolters Kluwer; 2022.

3. Amiel-Tison C, Gosselin J. Neurological development from birth to six years. Pediatr Neurol. 2001;24(2):77–85.

4. Bates B. Bates’ Guide to Physical Examination and History Taking. 13th ed. Philadelphia, PA: Wolters Kluwer; 2020.