Practice Perfect 807
Tenderizing the Foot - A Look Back

I often receive questions from students about what papers they should read. That’s obviously a tough question, leading to a very long bibliography of papers (there’s a ton to know!). But sometimes it’s informative to review milestone papers to improve our understanding of a topic. Let’s do that today with a quick synopsis and analysis of the paper, Tenderizing the Foot by the late Paul Brand, MD, a luminary in the field of diabetic foot disease1.

This paper from “way back” in 2003 covers concepts that today may seem elementary and well-known but are poorly appreciated by the average provider. For example, Brand begins the paper with a discussion of the physiology involved, specifically the relationship between two types of skin receptors, high threshold mecho-receptors (HTMs) and polymodal nociceptors (PMNs). HTMs respond to high levels of force, while PMNs respond to lower force but need chemical activation to send a pain signal. Brand’s “tenderization” referred to in the paper’s title is activation of the HTMs, lowering the pain threshold with continued walking and thus perceived pain carried by the PMNs. We do not feel pain with every step because the PMNs are not activated. However, when this system stops working, as with diabetic peripheral neuropathy, the PMNs are not activated, and those patients do not feel pain, allowing damage to the skin and subsequent ulceration. 

Dr Brand then goes on to discuss experiments he conducted to characterize the process of tenderizing the foot with the intent to look for clinical stigmata of this sensitization process. He describes having a test subject run barefoot around their hospital for eight miles and then using a sensor to examine changes in surface temperatures, using this as an “index of the tenderizing” process. Can you imagine running barefoot for eight miles and then having someone scan the temperature of your foot? Incredible! I simply love the description of the way the temperature distributions on the bottom of the runner’s feet change as the miles go on. Brand describes what increased lateralized temperatures as the runner increasingly lateralizes pressures from the great toe and first metatarsal head toward the lateral border of the foot. The temperature changes clearly tracked along areas of increased pressure which changed due to the body’s perception of pain, resulting from the HTM sensitization.

He then did a similar experiment using rat footpads, anesthetizing the rats, and having them receive repetitive pressures from a special machine each day for seven days. He sacrificed one rat a day and performed photomicrographs of the footpads to look for histologic changes over time. This experiment showed the entire process of tenderizing the foot, ending with ulceration. 

But not to be outdone by the rats, Dr Brand performed the same experiment on himself! This is truly one of my favorite things of all time. Using a finger instead of his foot, he subjected himself to the same machine used on the rats. As the number of repetitions built, he noticed increasing pain. His description of how he felt is truly priceless: “I would have started ‘limping’ by offering another finger to the machine before my day’s quota was complete, but instead I simply withdrew with dignity.” The next day he repeated the experiment on the same finger, stating, “…in less than 1,000 beats my devotion to science was severely tested.” That’s priceless! Can you imagine seeing comments like that in the Journal of Foot and Ankle Surgery? I wish I could have known Dr Brand!
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His conclusion is to recommend personal temperature monitoring and counseling patients when they see the temperature rise – the index of tenderizing the foot – and then act as if they are injured, decreasing walking activities and offloading the part of concern. He then advocates for a method to monitor temperatures in a more dynamic way. This elegant study is both a beautiful piece of medical history and a convincing argument for better understanding how the foot can be tenderized, leading to ulceration in the insensate population leading to practical applications for ulcer prevention. To this day, I find it odd that although others took up this idea and advocated for personal skin temperature monitoring, this concept does not seem to have taken off. I’m sure that with a greater appreciation for the wonderful work Dr Brand did we would see this method in much more common use – much to our patients’ benefit. 

Best wishes.

Jarrod Shapiro, DPM
PRESENT Practice Perfect Editor
[email protected]

  1. Brand PW. Tenderizing the foot. Foot Ankle Int. 2003 Jun;24(6):457-461.
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