Haywan Chiu, DPM, is a practicing podiatrist in Albuquerque, New Mexico. He has a special interest in the diabetic foot. Haywan runs Diabetic Foot Guardian, an easily digestible resource for patients regarding feet and diabetes.
Callus Debridement Can Be Diagnostic
Calluses form when shear forces and pressure induce the epidermis to reinforce itself. In patients with diminished pain sensation such as in diabetic neuropathy, continued friction from shear forces and pressure evolves the callus into a blister, then a blood blister (figure 1). When I see a bloody foot callus, I know that at some point, there was a break in the dermis. I don’t know if it has healed on its own or if it has expanded into a full blown ulcer because I can’t see past the callus. In fact, some calluses can be so thick I can’t even see the blood underneath! The only way to find out what’s hiding is to debride the callus.
Calluses and Osteomyelitis
It may seem like these two have nothing in common, but in the foot, they are connected like the earlobe is to the eardrum. In feet, the distance between skin and bone is very short; thus, the overwhelming majority of foot osteomyelitis is by contiguous spread. Foot osteomyelitis is often successfully treated with a combination of antibiotics and surgery. However, the wound, whether closed by primary or secondary intention, usually leaves a scar covered by a callus (figures 2-3). This callus can be bloody from drainage of the old wound. In the final clinic follow-up visit, a final callus debridement is performed to confirm that the wound is indeed closed. This clinical scenario can become more challenging if the patient develops sepsis from another source.
After contiguous spread osteomyelitis has been treated, follow-up x-rays and MRI may still show signs of chronic osteomyelitis. If the wound is closed, we can presume that the bone infection is either completely gone, or the body will take care of the rest. If the patient develops sepsis, you now have a sick patient with a bloody foot callus, with recent imaging reports stating there is a concern for osteomyelitis in the foot. It’s tempting to tunnel-vision the infection workup towards the foot as the most likely culprit. A quick way to rule out the foot as the infection source is to debride the callus. If there is no wound underneath and the foot does not look red or swollen, then it is not your source of infection.
Tools of the Trade
You can use #10 or #15 blades and/or disposable dermal curettes. Small (3 mm) dermal curettes remove the least amount of tissue per scrape, so it is easier to control and may be a good tool to use if you’re uncomfortable (figure 4). However, the workhorse of callus debridement is the blade. There are situations where I use both instruments for a single lesion. You will get a feel for what works for you with experience.
Technique, Tips, and Tricks
I got started by debriding an orange at home in my early training. Consider asking a foot specialist for supervision. Think of the callus as a small bump, and take slices or scrapes parallel to the skin until you get down to the level of normal skin. At first, you want to take as thin a slice as possible. After every 2-3 slices, feel the callus with your thumb to get an idea of how much callus tissue remains. It is easier build a mental image of the callus by feel rather than by look, because hyperkeratotic epidermis can vary in transparency.
As a safety precaution, understand that dull blades are much more dangerous than sharp blades. As the blade dulls, it becomes harder to control and you need to use more force to get through the tissue, thus increasing your chances of slipping and cutting yourself. Use as many fresh blades as you need to get the job done safely.
Iatrogenic injury is inevitable
Lastly, it can be intimidating when you’re close to dermis for fear of cutting the patient. You will occasionally cut too deep. As long as you take careful thin slices using only sharp blades, any iatrogenic injury will be very minor and will heal on its own. Remember, you’re trying to rule out an ulcer. If you miss the ulcer because you didn’t go deep enough, that is a much bigger problem than a small clean knick that will heal on its own.