The origins of the deep tendon reflex exam


The history of the reflex exam is very long and has taken many twists and turns. 
Galen and Aristotle wrote about involuntary movements that were not controlled by the will/soul [1].
Renee Descartes touched on the subject in the 1660's with a description of a foot withdrawing from a hot fire in which the "refleschis" or reflex was movement that engaged the nervous system by bypassing the 'soul' which resided in the pineal gland [1]. 
Much later, in the late 1800s, foundational work by Wilhelm Erb, Joseph Babinski, Carl Westphal and William Gowers developed the basis of the reflex examination as we know of it in current times. 
Erb studied the deep tendon reflex phenomenon and described, in great detail, a systematic approach to the reflex neurologic exam and is considered a co-discoverer of the muscle stretch reflex with Westphal in 1870-71. 
Carl Westphal recognized reflexes and called them "Unterschenkel Phänomen", or lower leg phenomenon in 1871.
Babinski focused on finding reliable signs that could differentiate organic from psychiatric or 'hysterical' paralysis prior to his famous report on the Babinski/plantar reflex in 1896. 
Gowers spent a significant amount of his career studying the knee jerk reflex as he realized that it was a commonly experienced phenomenon of the human body, to which was not well understood at the time. Gowers stated in one of his works in 1878, "...it is not a little curious that this knee-jerk, which has for generations amused schoolboys, should have become an important clinical symptom."
Soon after these basic observations, academic communities begin to quantify reflexes by using reflex severity scales. The first recorded scale was by Silas Weir Mitchell and Morris Lewis in 1886, where they broke down the reflex response with '-' for diminished response, 0 for absent response, and '+' for increased response. '--' and '++' were the extreme ends of this scale system. Many permutations of this original scale have been reported, including one by a prominent group of Mayo Clinic neurologists in 1956.
Throughout the second half of the 20th century, extensive advancements have been made in neurologic science pertaining to our understanding of the neurologic system and the complex nature of the deep tendon reflex physiology. What hasn't changed much since these early days, is the reflex hammer itself. Some variance in hammer shape and style have been used, including the Taylor, Queen, Babinski, and Tromer hammers to name a few. But the underlying technology of a rod and hammer head has not significantly changed, and to this day medical students and clinicians still teach the ways of the founders who initially described this all in the 1870s. 
Our team decided to create RFX Hammer for many reasons, including the need for technological advancement in the examination. We hope that our users see RFX Hammer as a natural evolution of this multi century story of reflex examinations. We reflected on what has been learned over the centuries, and built RFX hammer by going back to the first principles of the reflex examination. RFX Hammer has a classic Queen hammer style, but incorporates a force-based sensor system to provide real-time feedback to users so they can better understand their patient's physiology and pathology, while providing a way to improve consistency between exams. 
Our team is definitely not as visionary as the founders who observed this important clinical sign, but we hope to stand on the shoulders of these giants with RFX Hammer.
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Much of the historical review in this article was obtained by the excellent review article written by Christopher J. Boes in the Journal of Neurology 2014 (link: https://pubmed.ncbi.nlm.nih.gov/24695995/).

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