Preventing the Burn: Is There a Role for AFOs in Mitigating the Pain of Claudication?

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By Phil Stevens, MEd, CPO, FAAOP

Peripheral arterial disease (PAD) is a substantial problem, affecting as much as 10 percent of the general population and 20 percent of people over 70 years old.1 Affecting an estimated 8.5 million adults in the United States, PAD is caused by the progressive buildup of atherosclerotic plaques that limit blood circulation to the lower extremities.2 The most common clinical manifestation of PAD is intermittent claudication, a pronounced pain in the muscles of the leg that is induced by activity and relieved by rest.1 The recommended treatment for claudication includes exercise training to improve walking. However, such community-based exercise programs are often undermined by the pain associated with claudication in the calves.2 The problem then becomes circular, as the pain of activity discourages future activity, leading to additional negative impacts on general health and well-being. Often, it is the pain associated with intermittent claudication that leads to lower-limb amputation, but not before attempts to reduce the associated pain have led to general reduced activity.

A number of publications have begun to explore the application of AFOs in this population to partially substitute for the function of the calf muscles and reduce the pain associated with intermittent claudication and improve activity levels in patients with PAD.2-4 This article reviews the findings of this small but expanding body of literature.

Walking Times

In one such study, investigators identified 12 adults with PAD in which calf pain was reported as the primary limiter to walking.2 These subjects were fitted bilaterally with Ottobock WalkOn Reaction AFOs by certified orthotists and provided with a one-week acclimation period. Following the accommodation, the subjects were assessed with and without the AFO at baseline and 12 weeks later. Key assessments included the peak walking time, or the maximal time a patient could walk on a treadmill before stopping due to secondary severe leg pain. Also recorded was the claudication onset time, or the walking time prior to the initial presentation of calf pain.2

In addition to the structured treadmill tests, a more functional performance measure was documented in the form of a six-minute walk test (6MWT). Observations included the walking distance as well as the claudication onset distance, or distance traveled before the onset of calf pain.2

Following the baseline assessments (collected on two separate days with subjects randomized to the order of the conditions), the subjects were advised to walk as much as possible with the devices. Recommendations included walking to induce moderate leg pain followed by rest until the pain subsided. Walking and resting were advised for a cumulative period of 35-50 minutes with sessions occurring three times per week for 12 weeks.2 At the conclusion of 12 weeks, follow-up assessments were collected on separate days, both with and without the AFOs during testing.

The results were fairly striking. With respect to treadmill testing, after 12 weeks of AFO use in the community, patients were able to walk an average of 35 percent longer in the no-AFO condition. When using the AFOs, even greater improvements were realized with patients walking an average 65 percent longer at the follow-up assessment. Significant improvements were also realized in the mean times to claudication onset, which increased by 60 percent in the no-AFO assessments (from three to almost five minutes) and 63 percent in the AFO assessments (from just over four minutes to seven minutes).2

Similar benefits were observed in the more pragmatic observations associated with the 6MWT. In the no-AFO condition, the 12-week program yielded an average increase of 20 percent, from 295 meters to 356 meters. Similar benefits were observed in the with-AFO condition with an improved mean baseline performance of 318 meters increasing to 354 meters. Additional benefits were observed in the distance to the onset of claudication pain. In the no-AFO trials, it increased 44 percent from an average of 126 meters to 182 meters, while in the with-AFO trials, it increased 35 percent from an average of 164 meters at baseline to 222 meters following the 12-week program.2

Collectively, this trial observed a number of trends. First, during the baseline assessments, the use of AFOs immediately increased the mean time and mean distance to the onset of claudication pain (3 minutes versus 4.3 minutes in treadmill testing and 126 meters versus 164 meters in the 6MWT).2 In addition, the increased activity levels enabled by the 12 weeks in the AFO program led to improvements in endurance and substantial delays in the onset of claudication pain even without the AFOs in baseline and follow-up testing as previously described.

Finally, the most striking improvements were found in comparing the baseline no-AFO performance values against the follow-up values observed with the AFOs, particularly with respect to delaying the onset of claudication pain. During treadmill testing the mean time to claudication increased from three minutes to seven minutes. With respect to the 6MWT, the distance travelled prior to the onset of claudication pain increased 78 percent from 125 meters to 222 meters.2

Patient Perspectives

While the data appears to suggest both immediate and sustained value of the AFOs with respect to walking endurance and delaying claudication pain, additional insights were subsequently gained through structured interviews with the participants published in a separate paper.3 Data was collected through a series of three separate small focus groups conducted by an experienced interviewer with no prior involvement in the original AFO study. Open-ended questions were used to prompt dialog within the focus groups. For example, "Discuss the impact the device has on pace, distance, and comfort of your walking," and "Compare your participation in in- and out-of the home activities since getting the device."3

Quotes taken from these interviews affirm what the previously described data suggested. With respect to the impact of the AFOs on walking ability and quality of life, one subject reported, "Before I got [the AFOs], I could walk a block before I started cramping up in the back of my legs. I put these on and after I got home, I walked about four blocks before it even started to hurt." A second participant echoed similar benefits. "I might take three little short pauses in the course of walking 25 minutes (while wearing the AFOs). Whereas before I was walking three minutes, taking two minutes to rest to let that severe cramping go away." A third participant was more direct, "[If] I was wearing my braces, I know darn well that I could go a whole lot further and a whole lot faster and not have any pain."3

Several participants spoke to the impact of the increased activity enabled by the AFOs on walking ability without the AFOs. "I know I walk a lot further, even without them now. And I have to attribute it to that [AFO]." A second participant added, "I've done 20-25 minutes without stopping and it's not the cramping that stops me. It's the sore knees because my arthritis is getting worse in my knees." A third participant said, "[My] exercise is more than it used to be. Probably more than ever before."3

Additional statements suggest the profound impact increases in activity can have in this population. One subject asserted, "They [the AFOs] have definitely contributed to how happy I feel. Being in better shape…so my overall health is better, and attitude is better because my health is better." A second subject elaborated, "I was willing to try these [AFOs], and before I was kind of depressed. I was depressed because I didn't know if I was going to make it. I didn't know how far I could walk…and now it's given me hope…. Any time I feel like I am going to struggle—guess what, the device comes out. If the pain starts coming back or I need to use them or something, I know that they are there." A third participant spoke to the relationship between the AFOs and his hobby of dancing. "Now I can go to the dances down at the Elk's and maybe do one dance or maybe two and can do the whole dance. When I don't have those [AFOs] on, I can maybe do half the dance and I have to go sit down or else I'm going to fall in the middle of the floor."3

Collectively, this work confirmed that patients largely experience a relief of claudication symptoms that allow them to increase their walking distances, durations, and speed. This decrease in the frequency and severity of claudication pain also reduced the general needs for intermittent rest, or the duration of those rests before resuming walking activity.3 Some patients elected to stop using the AFOs at the conclusion of the 12-week clinical trial, but reported sustained benefits to walking and quality of life from the increased activity experienced during the trial. These patients described a persistence in the improved walking capacity and pain-free walking distance even after AFO use had concluded. The community-based walking program enabled by the AFOs led to reports of increased confidence, happiness, and quality of life.3

Underlying Mechanisms

Research from a separate institution has explored the underlying mechanisms that appear to be delaying claudication pain and increasing exercise capacity.4 These authors describe the role of atherosclerotic plaques associated with PAD in limiting the blood flow to the lower extremities. The limited blood flow leads to the walking-induced leg pain that is the most common manifestation of PAD. The underlying cause of this claudication pain appears to be the reduced muscle oxygenation values in the calf muscles of patients with PAD compared to healthy controls, values that are both lower at resting baselines and decline more quickly with activity. By absorbing and returning mechanical forces during gait, AFOs appear to decrease the demands upon the calf muscles thereby improving the muscle oxygenation levels in this population.4

To test this premise, subjects with PAD were recruited to undergo similar to the aforementioned treadmill testing with the addition of a muscle oxygen monitor attached to their gastrocnemius muscles. The subjects then indicated the onset of claudication and the point at which claudication pain precluded further walking. Treadmill testing was conducted with and without the use of AFOs. The authors reported an increase of approximately 30 percent in muscle oxygen saturation levels with the use of the AFOs, providing a mechanism for increased walking distances and delayed claudication pain.4

Summary

Patients with PAD are caught in a cyclical circuit of increasing inactivity. While they would benefit from increased walking and activity levels, the pain associated with claudication precludes their ability to engage in meaningful exercise and activity. The mechanism for this pain appears to be the reduced oxygenation in the muscles of the calf frequently observed in this population that declines even further with activity. By supplementing the concentric and eccentric forces acting upon the calf muscles, it appears that AFOs may reduce the oxygen requirements to those muscle groups, delaying the onset of both initial claudication and full claudication that precludes further walking.

The pilot data published to date suggests that once claudication pain is reduced and delayed, patients are able to increase their physical activity levels and endurance, with supplemental benefits to their overall health and well-being. While additional research is needed to understand the AFO designs that might optimize walking endurance and pain mitigation in this population, available data suggests that they may benefit from orthotic management.

 

Phil Stevens, MEd, CPO, FAAOP, is a director with Hanger Clinic's Department of Clinical and Scientific Affairs. He can be contacted at philmstevens@hotmail.com.

References

1. Hernandez, H., S. A. Myers, and M. Schieber, et al. 2019. Quantification of daily physical activity and sedentary behavior of claudicating patients. Annals of Vascular Surgery 1(55):112-21.

2. Mays, R. J., A. A. Mays, and R. L. Mizner. 2019. Efficacy of ankle-foot orthoses on walking ability in peripheral artery disease. Vascular Medicine 24(4):324-31.

3. Choma, E. A., R. J. Mays, R. L. Mizner, and A. M. Santasier. 2020. Patient perspectives of ankle-foot orthoses for walking ability in peripheral artery disease: A qualitative study. Journal of Vascular Nursing 38(3):100-7.

4. Arellano, A., H. Rahman, I. Pipinos, J. Johanning, and S. Myers. 2019. Muscle oxygenation in patients with peripheral artery disease during walking with and without an ankle foot orthosis. University of Nebraska Omaha Student Research and Creative Activity Fair. Accessed at https://digitalcommons.unomaha.edu/srcaf/2019/Schedule/81/ on 9/12/2020.