The early history of the knee-jerk reflex in neurology.

Medical interest in the knee-jerk reflex began in about 1875 with simultaneous and independent publications by Wilhelm Heinrich Erb (1840-1921) and Carl Friedrich Otto Westphal (1833-1890) contending that the knee jerk was absent (and the ankle clonus was present) in all clear cases of locomotor ataxia (tabes dorsalis). Physicians in the medical communities of Europe, Great Britain, and North America responded with case and large group studies that tested this contention. These studies revealed the usefulness of the knee jerk and other myotatic reflexes, but also unexpected characteristics. The knee jerk, apparently so simple, proved to be a complex phenomenon depending the strength of the strike on the patella, induced muscle tension, and inhibition from the brain. Was it a reflex with afferent and efferent nerves and an intervening process in the spinal cord, or was it a local phenomenon confined to the muscle itself? Experimental studies directed at the reflex issue investigated latencies from patella strike to leg extension or muscle contraction and compared them with latencies from direct muscle strikes and theoretical calculations based on reflex components. Such studies were unable to resolve the reflex issue during the nineteenth century. The physicians were shown to be limited, like all scientific explorers of the unknown, by their knowledge, methodology, and technology.