Charles Gilbert Chaddock introduced the External Malleolar sign as an alternative to Babinski reflex in 1911. This was later referred to as Chaddock reflex. Kisaku Yoshimura described a very similar sign in 1906 in the Japanese medical literature as a variation on the Babinski sign. Both the Chaddock reflex and the Babinski reflex test the integrity of the corticospinal tract (CST). Both reflexes are easy to elicit and do not require significant cooperation from the patient, and therefore can be performed in patients who cannot fully cooperate with the neurological exam. The Babinski reflex is more commonly utilized as part of the routine neurological exam. However, alternatives such as Chaddock sign can be employed when the patient exhibits a significant withdrawal response to plantar stimulation when performing the Babinski reflex.
The CST originates from the cerebral cortex in layer V cells (Betz cells). Sixty percent of fibers are from the primary motor area, premotor area, and supplementary motor area. Other fibers originate primary sensory area, parietal cortex, and parietal operculum. The CST descends through the internal capsule and brainstem (forming the pyramids in the medulla). At the medullary spinal junction, 75% to 90% of fibers decussate and forms the lateral CST (contralateral), and the remainder form the anterior/ventral CST (ipsilateral). The lateral CST synapses directly with IX neurons (anterior horn cells) or on interneurons in Layers V to VIII. The CST is the upper motor neuron (UMN), and the alpha motor neuron is the lower motor neuron (LMN). Together, the UMN and LMN control motor function.
When the lateral aspect of the foot is stroked with a dull instrument, this triggers afferents which mediate nociception stimulation of the S1 dermatome. The sensory input travels up the tibial and sciatic nerve to the S1 nerve root and triggers an efferent response at that spinal level causing downward contraction of the toes. The CST normally prevents the spread of this reflex to other nerve roots. When there is a pathological process that leads to dysfunction of the CST, there is spread of this sensory stimulation to adjacent nerve roots L5, L4, L3, L2, which leads progressively to increase in flexion (shortening) of LE. One observes deviation (dorsiflexion) of the big toe upward and fanning of the other toes. This is a positive Chaddock reflex.
The Babinski reflex is part of the routine neurological examination to evaluate the integrality of the CST. However, in the setting where the patient has significant withdrawal to plantar stimulation, or if there is a lesion (such as an infection) on the lateral plantar aspect of the foot, then the Chaddock reflex offers a reasonable alternative. In the setting of stroke and spinal cord injury, the presence of this reflex may be an early indication of these emergent conditions.
Generally, a dull instrument is used to perform the Chaddock reflex. A sharp instrument should be avoided to prevent pain or injury to the skin. Traditionally, the end of a reflex hammer, a tongue depressor, or edge of a key are utilized to elicit this reflex.
The patient should be relaxed and comfortable when the examiner performs the Chaddock reflex. The patient should be advised that the sensation may be slightly uncomfortable. Patients may experience a tickling sensation, but this is less likely than with Babinski reflex which requires plantar stimulation. The examiner should ensure that the dorsolateral aspect of the foot is free of any lesions before proceeding.
Chaddock's reflex is elicited by stimulating the dorsolateral aspect of the foot from the posterior portion of the skin just beneath the external malleolus anteriorly and along the external edge of the foot. Both the Chaddock's and Babinski's reflex lead to flexion of the big toe and fanning of the other toes when there is dysfunction of the CST.
Both the Babinski and Chaddock reflex test the integrity of the CST. When a lesion occurs anywhere along this CST, the examiner may obtain a positive reflex. The examiner watches for dorsiflexion (upward movement) of the big toe and fanning of the other toes. This is referred to as a "positive reflex," or one may state that the "reflex is present." When there is a downward deviation of the toes, this means the reflex is absent. The absence of the reflex suggests that the CST may be intact. If there is no response, this is considered a neutral response and has no clinical significance.
Infants have an incompletely myelinated CST, so a positive Babinski or Chaddock reflex in the absence of other neurological deficits is considered benign up to 2 years of age.
In comatose patients, one may see a triple flexion response. In this case, one observes dorsiflexion of the big toe, fanning of the other toes, dorsiflexion of the foot, as well as knee and hip flexion. This represents profound dysfunction of the CST, with the spread of the reflex to the L3 and L2 myotomes. Care must be made to distinguish this from a withdrawal response. The triple flexion response is very stereotyped whereas the withdrawal response varies with each stimulation.
The advantage of Chaddock reflex over the Babinski reflex is that it may minimize withdrawal due to plantar stimulation. Because the CST has a long course, the presence or absence of these reflexes are useful in determining the health of the central nervous system.
Alternative methods for eliciting this response have been developed. In each case, the examiner watches for upward deviation of the big toe and fanning of the other toes. Below are some of the alternative methods: