Which removable offloading device is better to heal diabetic foot ulcers?

Non-removable knee-high offloading devices are the globally-recognised gold standard treatment to most effectively heal plantar diabetic foot ulcers. This is because they have been found to be the most effective in reducing plantar pressure and daily activity on the ulcer area, and adherence is enforced.

However, these devices are contraindicated in some patients and some others just refuse to wear them. That means that removable offloading devices are often still required in daily clinical practice. But up until now which removable offloading device to choose for best ulcer healing had not been investigated.

Now a new study from DFA’s friend and global diabetic foot offloading guru Dr Sicco Bus published in the International Wound Journal suggests that three very different removable devices are equally as effective on ulcer healing. But is that the full story?

This randomized controlled trial investigated the outcomes of three removable offloading devices. The authors recruited 60 patients with non-infected plantar diabetic foot ulcers from Dutch and German multidisciplinary diabetic foot clinics. They randomized these patients to wear one of three removable offloading devices while continuing to receive good quality care for 20 weeks or until their ulcer healed.

The devices were a:

1. Customized removable knee-high cast: Bivalved total contact cast (‘knee-high cast’),;
2. Customized removable ankle-high cast: Contact cast built up to the ankle (‘cast shoe’);
3. Prefabricated removable ankle-high shoe: Forefoot offloading post-operative boot (‘prefabricated shoe’)

After 2 weeks of wearing these devices they then very cleverly measured the plantar pressure, average daily steps and non-adherence rates in these patients. They did this to represent a measure of the typical plantar pressures, daily activity and adherence for each device. What they found was fascinating.

In short, they found no statistical differences in healing rates at 12 weeks or 20 weeks between the three devices. This suggests it doesn’t matter which of these removable offloading devices a patient wears, as they all healed around 60% of ulcers at 12 weeks and 80% at 20 weeks. However, what was really interesting was the variability the found between the effects of the three devices on plantar pressure, daily steps and adherence. These factors seemed to balance each other to give a similar overall ‘cumulative plantar stress’ level when wearing each device, and similar healing rates.

First, the knee-high cast group had the lowest average peak plantar pressures (81kPa) compared to the cast shoe (176kPa) and prefabricated shoe (107kPa); all groups reported >200kPa in their regular shoes. Second, the prefabricated shoe group recorded the highest daily steps (~8,900) compared to the knee-high cast (~8,300) and cast shoe groups (~7,000). Third, the knee-high cast group had the highest non-adherence to wearing the device (17%) compared to the cast (5%) and prefabricated shoe (5%). Fourth, patients wearing the knee-high cast had the highest rate of drop out for refusing to wear the device (25%) compared to the cast (5%) and prefabricated shoe (5%). And last, the cast shoe group had the highest number of serious adverse events (20%) compared to the knee-high cast (15%) and prefabricated shoe group (10%).  However, only the plantar pressures were statistically different between the three groups for those factors, even though they were all descriptively different.

Put simply, this seems to mean that the group wearing the knee-high cast had the lowest plantar pressures, mid-level daily activity, but highest non-adherence compared to the other devices.  The cast shoe had the highest pressure pressures, lowest daily activity and low non-adherence. And the prefabricated shoe had mid-level plantar pressures, highest daily activity and low non-adherence. These factors combined, seem to balance out to provide an equivalent overall ‘cumulative plantar stress’ level on the ulcer area no matter which device was worn. This cumulative plantar stress is a relatively new concept in diabetic foot ulcer care which we dare say you will hear much more of over the next decade.

For clinical practice, this means that instead of worrying only about reducing pressure (plantar pressure), we also need to worry about how often this pressure occurs (daily steps) and of course this is all impacted by how often the patient wears their device (adherence). These results suggest that if the patient cannot wear a non-removable offloading device, then it’s not simply a case of choosing any other device, but it’s important to marry up the effects the device you chose will have on reducing your patient’s plantar pressure, daily activity and adherence to wearing that device.

While this study had many strengths – i) randomizing patients with very similar demographic and ulcer characteristics; ii) measuring a range of different plantar pressure, activity, adherence and adverse event factors; iii) following patients for 20 weeks – it did have a number of limitations.  These included: i) they took 10 years to complete the study because they recruited patients in two time periods so standard treatment may have changed over that time, however they found no differences for this between the two time periods; ii) all groups were well matched except the knee-high cast group had more deep ulcers than other groups; iii) non-adherence was self-reported which has questionable reliability; iv) they only measured the plantar pressure, activity and adherence for every second patient in each group and only after 2 weeks wearing the device. We know from another of DFA’s friends Prof Bijan Najafi that activity changes over time in those wearing removable devices to heal foot ulcers.

In conclusion, the authors “cautiously suggest that when a non-removable offloading device is contraindicated … each of these three (removable) offloading devices may be … used”. However, perhaps most importantly they “stress the importance of a continuously reduced cumulative stress level on the foot through effective offloading, high adherence and lower ambulatory activity level in healing neuropathic plantar forefoot ulcers”.

But after all that it’s very important to remember … that non-removable knee-high devices are still the international gold standard offloading device because …. they reduce the most plantar pressure, daily activity and enforce adherence, and therefore reduce the most overall cumulative plantar stress.