On June 13th, 2017 we learned about

The debates and designs that resulted in the humble rubber reflex hammer

Today, while waiting in the doctor’s office for a checkup, my second grader proudly announced that she recognized the reflex hammer sitting on the counter, and that she’d figured out how to replicate its function with both her hand and lunchbox. When the doctor actually tested my daughter’s patellar ligament, there was a little disappointment that the iconic rubber hammer wasn’t used, as the doctor struck her knee with the rubber edge of her stethoscope instead. The stethoscope was effective at triggering the reflex, maybe even better than a well aimed lunchbox, so how did these hammers end up in doctors’ toolkits in the first place?

Medical grade rubber hammers were originally designed to look for fluid built up in people’s chest cavities. After seeing innkeepers thump the side of wine casks to hear how full they were, Dr. Leopold Auenbrugger suggested hitting chests with a percussion hammer to see how hollow they sounded. The idea caught on, but the design was criticized and reworked from all corners. Potential replacements looked like everything from a battle axe to a magic wand. Rubber wasn’t locked down as a material either, as doctors considered whacking their patients with ebony, whale bone, brass, lead and velvety yarn.

Knocking knees for nerves

It wasn’t until 1875 that Drs. Heinrich Erb and Carl Friedrich Otto Westphal noticed what’s been fascinating my daughter— tapping a tendon or ligament can cause the associated muscles to automatically flex and relax. The patella ligament under your knee, for instance, sends a signal through your spine to your alpha motor neuron, which then activates your quadriceps in your thigh. This response is normally used by the body to automatically maintain posture and balance without worrying about it, but for doctors it’s a handy way to diagnose an array of possible maladies. When a knee is jerked more or less than expected, it can help reveal where in the body other symptoms might be stemming from.

The iconic triangular, rubber hammer you’re likely to see at the doctor’s office was developed by Dr. John Madison Taylor in 1888. The design hasn’t changed a lot since then, but it’s not the final iteration of reflex hammers at doctors’ disposal. If the nervous response of other parts of the body are to be tested, a variety of more specialized hammers are available, such as the Krauss hammer that was designed by Dr. William Christopher Krauss. Some have large round heads for knees, small balls for biceps, and thinner structures for stimulating the skin. Of course, if all else fails, a good thump from a thumb might still do the trick as well.

Source: Digital Schmigital: After 130 Years, Reflex Hammer Still Going Strong by Bret Stetka, KQED Future of You

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