The deep tendon reflexes (DTR), particularly the tricep, patellar, and Achilles reflexes, were initially described by Wilhelm Heinrich Erb and Carl Friedrich Otto Westphal in adjacent articles simultaneously published in 1875 in the German Archives for Psychiatry and Nervous Diseases. Since then, the Achilles reflex test, also called the ankle jerk test, has remained an essential component of the lower extremity neurologic exam. It is a myotatic (deep tendon) reflex that can be elicited easily with a reflex hammer to assess the S1 nerve root of the lumbosacral plexus. As for all deep tendon reflexes, the Achilles reflex is then interpreted by grading the response using a 0 to 4 scale and comparing it to the contralateral limb and nearby reflexes.
Examining the DTRs such as the Achilles reflex provides insight into the function of the reflex arc and its' symmetry or lack thereof when compared to the contralateral side. Deep tendon reflexes remain an essential component of the neurologic exam that can guide further clinical decisions and differentiate between upper motor neuron and lower motor neuron pathology.
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