Any time a practitioner applies an orthotic device, such as an ankle foot orthosis (AFO) to offload a diabetic foot ulcer, he or she also has to make sure pressure is not redistributed to the point that a new ulcer is created elsewhere on the foot. Devices have to be constructed with the correct materials and properly fitted to the foot, which leaves a lot of leeway for practitioners.
“When you’re offloading an insensate foot you always have to remember not to overload the surrounding tissue,” said Dennis Janisse, CPed, president and CEO of National Pedorthic Services in Milwaukee, WI. “A lot of these patients can’t tell you if you’re putting too much pressure in a certain area. You can very easily cause another ulcer on the foot by putting too much pressure somewhere else to offload that area you’re targeting.”
Traditionally, offloading strategies have been determined by a practitioner’s experience and intuition, said David Sinacore, PT, PhD, associate professor of physical therapy and medicine at Washington University at St. Louis, MO. Now in-shoe pressure measurement devices can confirm offloading in the targeted area and also document areas where load is increasing as a result of the redistribution.
As in real estate, the primary issue is location, location, location. For midfoot or hindfoot ulcers Sinacore uses bracing above the ankle. If an ulcer is in the forefoot, offloading might be accomplished with the proper shoe and an in-shoe device, or, for severe cases, with removable cast walker.
“We don’t want anything rigid inside the shoe, so we make the sole rigid. That’s the key to offloading,” he said. “We make the shoe more rigid so that the foot doesn’t add to push off.”
In addition, the particular demands of a patient can influence how to offload, said David Armstrong, DPM, MD, PhD, professor of surgery and director of the Southern Arizona Limb Salvage Alliance at the University of Arizona in Tucson.
“If a highly active patient has a wound, the situation might demand a robust offloading modality such as an AFO. However, someone who is less active may require something like healing sandals,” he said.
How does a practitioner know the offloading is effective?
“Unless you’re actually measuring it, you don’t,” Armstrong said. “That probably calls for us to do a better job of affordably measuring offload in a larger number of patients. Measuring what we manage is really important.”
Pressure measurement systems may not be practical for some practitioners, but there are also lower-tech ways to assess offloading.
Janisse suggested paying close attention to changes in the softer orthotic materials to help determine the effect of offloading measures.
“After a week, if the area of offloading has bottomed out and the area around it is still an eighth of an inch, that would indicate that you could probably increase your offload because you haven’t adequately relieved the area you thought you were offloading,” he explained.
To guard against accidental overloading of nontarget areas, Sinacore asks patients to examine their feet regularly for skin redness and to acclimate gradually to orthotic devices by wearing them an hour a day, then for longer each day until they reach eight hours of wear a day.
Pressure measurement devices also can’t measure the effect of shear, another contributing factor in diabetic foot ulceration that practitioners should try to address when prescribing offloading devices.
“For all practical purposes, when we’re talking about offloading, we’re talking about relieving pressure,” said Janisse. “Pressure is easier for us to understand. We can see impressions and depressions. We need to understand friction and shear.”
Socks can help decrease friction and shear, he added.
Janisse prefers offloading an orthotic device from the bottom to padding or making other adjustments to the aspect of the orthosis that is closest to the foot.
“The relief you’re building on the bottom of the orthosis is much more gradual,” he said.
“You don’t want to have real severe edges right next to the foot.”
Sponsored by an educational grant from Toad Corporation