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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.[1] 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.[2][3] 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.[2][4][5]

The Achilles tendon reflex is a simple maneuver that is part of any lower extremity neurologic exam. It can be performed relatively easily both in the clinic and inpatient environment. However, differences in technique and experience can lead to varying intra-patient results. Various case-control studies have been published that compare the traditional Achilles tendon tap to the plantar tap and the reproducibility across different experience levels (Level 3).[12][23][13] When comparing the two Achilles reflex methods, it was shown that the traditional Achilles tendon tap had less inter-observer and intra-observer reliability.[12][23][13] The plantar tap method had greater reproducibility. When comparing senior-level physicians to junior level, the plantar tap had significant inter-observer reliability (p < 0.001).[23] The intra-observer reliability was not significant in the senior level practitioners but did show a significant difference for the junior level physicians (p < 0.05).[23] Additionally, 84% of ankle jerks would have initially been called absent if final-year medical students would not perform a plantar tap method for confirmation.[12] The ubiquitous nature of the Achilles reflex test and its use by senior physicians, junior physicians, medical students, nurses, and physician assistants, necessitate a reliable confirmatory alternative. Considering the interdisciplinary structure of patient care teams with varying levels of experience, it is prudent to consider using the plantar tap method. Particularly for patient populations that you may suspect a diminished or altered reflex response, such as the elderly, diabetic, and hypothyroid patients.