Extended effects of a wearable sensory prosthesis on gait, balance function and falls after 26 weeks of use in persons with peripheral neuropathy and high fall risk-The walk2Wellness trial

Abstract

Background: We recently reported that individuals with impaired plantar sensation and high fall risk due to sensory peripheral neuropathy (PN) improved gait and balance function following 10 weeks of use of Walkasins^®, a wearable lower limb sensory prosthesis that provides directional specific mechanical tactile stimuli related to plantar pressure measurements during standing and walking (RxFunction Inc., Eden Prairie, MN, United States). Here, we report 26-week outcomes and compare pre- and in-study fall rates. We expected improvements in outcomes and reduced fall rates reported after 10 weeks of use to be sustained.

Materials and methods: Participants had clinically diagnosed PN with impaired plantar sensation, high fall risk (Functional Gait Assessment, FGA score < 23) and ability to sense tactile stimuli above the ankle at the location of the device. Additional outcomes included 10 m Gait Speed, Timed Up and Go (TUG), Four-Stage Balance Test, and self-reported outcomes, including Activities-Specific Balance Confidence scale and Vestibular Disorders Activities of Daily Living Scale. Participants tracked falls using a calendar.

Results: We assessed falls and self-reported outcomes from 44 individuals after 26 weeks of device use; 30 of them conducted in-person testing of clinical outcomes. Overall, improvements in clinical outcomes seen at 10 weeks of use remained sustained at 26 weeks with statistically significant increases compared to baseline seen in FGA scores (from 15.0 to 19.2), self-selected gait speed (from 0.89 to 0.97 m/s), and 4-Stage Balance Test (from 25.6 to 28.4 s), indicating a decrease in fall risk. Non-significant improvements were observed in TUG and fast gait speed. Overall, 39 falls were reported; 31 of them did not require medical treatment and four caused severe injury. Participants who reported falls over 6 months prior to the study had a 43% decrease in fall rate during the study as compared to self-report 6-month pre-study (11.8 vs. 6.7 falls/1000 patient days, respectively, p < 0.004), similar to the 46% decrease reported after 10 weeks of use.

Conclusion: A wearable sensory prosthesis can improve outcomes of gait and balance function and substantially decreases incidence of falls during long-term use. The sustained long-term benefits in clinical outcomes reported here lessen the likelihood that improvements are placebo effects.

Clinical trial registration: ClinicalTrials.gov, identifier #NCT03538756.

Keywords: balance; clinical trial; falls; gait speed; neuromodulation; peripheral neuropathy; sensory prosthesis; wearable.

FIGURE 1

(Left) The two components of the Walkasins prosthetic device, the pressure sensitive flexible foot pad that is placed in the shoe and connects to the leg unit that contains a rechargeable battery, a microprocessor, supporting electronics, and four mechanical tactile stimulators. The embedded software algorithm evaluates pressure data and activates the mechanical tactile stimulators at relevant times during standing and walking to signal balance-related information to the afferent nervous system. (Right) A Walkasins user wearing the device in the process of turning it on. The Walkasins system is worn bilaterally (unilateral components depicted).

FIGURE 2

Flowchart of the walk2Wellness trial. Data for the primary endpoint at 10 weeks, shown to the right for reference, were published earlier (Oddsson et al., 2020). Due to COVID-19 site lockdowns, in-person outcomes could be assessed from 30 of the 44 participants. Self-reported outcomes and fall events were assessed from all 44 participants who reached the 26-week follow-up visit.

FIGURE 3

Comparing FGA scores at baseline (horizontal axes) with assessments after 2 (A), 6 (B), 10 (C), and 26 (D) weeks (vertical axes) of device use. Open symbols represent pre-study non-fallers and filled ones are pre-study fallers. Dashed lines show regression line for the whole group. Forty-four participants completed in clinic outcomes testing up to 10 weeks (primary endpoint), and 30 participants completed the 26-week assessment in person. Scores above line of equality indicate improvements and below a decrement in FGA score compared to baseline scores. Notice that regression line slopes are less than 1 indicating slightly larger improvements in FGA score for those with lower baseline scores. Overall, improvements observed after 2 weeks of use appeared sustained throughout the 26 weeks of use.

FIGURE 4

Averages of clinical outcomes across the in-person assessments at baseline (0), 2, 6, 10, and 26 weeks for the 30 participants (blue lines and symbols) who were able to be tested in clinic after 26 weeks of device use for the in-clinic outcomes FGA (A), TUG (B), gait speed (C,D), and the Four-Stage Balance test (E). Gray symbols and lines represent the pre-study non-fallers (n = 12 of 30) and orange lines and symbols represent pre-study fallers (n = 18 of 30). Notice that most improvements appeared to peak after 6–10 weeks of device use, followed by a leveling off until 26 weeks.

FIGURE 5

Illustration of changes in ABC/FGA ratio (left axis, solid lines), an indication of self-perceived balance confidence in relation to externally observed gait function performance, for participants with baseline ABC scores >67% (high balance-confidence, orange triangles) and those with ABC scores ≤67% (low balance-confidence, blue circles). The associated changes over time in FGA scores for the same two groups are also shown (right axis, dashed lines). Notice that both groups had similar FGA scores at baseline, which led to a dramatic difference in the ABC/FGA ratio at baseline. Over time, the ratio for the high balance-confidence participants gradually decreased and aligned with the low balance-confidence group at ∼3.5, mainly due to an increased FGA score and a maintained ABC score. The low balance-confidence group maintained an ABC/FGA ratio ∼3.5 throughout the 26 weeks associated with a proportional increase in ABC and FGA scores. Interestingly, the high balance-confidence group showed a higher increase in FGA score than the low balance-confidence group.

FIGURE 6

Accumulated number of falls reported 6 months pre-study (blue trace and blue dotted linear regression line) and falls documented in-study (orange trace and orange dotted regression line). The 53 falls reported for the prior 6 months would correspond to 0.29 falls/day (53/180∼0.29), which represents the slope of the regression line (blue trace). For illustration purposes, the 53 pre-study falls were randomly distributed across the 6 months since their exact time occurrence was unknown. In-study falls are shown as they occurred and were reported by participants throughout the 26 weeks. Notice how the rate of in-study falls appear to begin deviating from pre-study fall rate (slope of dotted blue line) after approximately 20 days of device use.