Development and Pilot Testing of a Surface Discrimination Test for People with Lower Limb Amputation

Introduction: There is a lack of understanding as to how sensory loss and sensory deficits impact those with LLA. The purpose of this research is to determine the extent to which people with LLA can discriminate between surfaces underfoot, in order to better understand the relationship between people with LLA and their perception of the ground they are walking on. We developed a test to determine which qualities of surfaces may be easier to distinguish. Methods: 10 unimpaired adults and 2 adults with LLA participated. Participants compared surfaces underfoot that consisted of ceramic, rough tile, gravel, sand, and sandpaper to span surface qualities of motility and roughness. With their vision obscured, participants were asked to take two steps onto two adjacent samples, with one sample underneath each foot. Each sample was compared against a ceramic control sample. Participants were asked to report if the samples were the “same” or “different”. Unimpaired adults completed trials with a standardized shoe and with the participant’s personal footwear. Discrimination scores were computed as the proportion of correct responses (% Correct) in total and by sample. For the unimpaired group, logistic regression analysis was used to obtain an odds ratio for correct discrimination, with pairwise comparison to detect any associations between independent variables (footwear, session number, sample, leading leg) and correct responses. Results: All participants were able to complete the testing protocol. For unimpaired participants, only sample had a statistically significant association with participant accuracy (p<0.001). Sandpaper achieved the lowest scores (%Correct=15%, 95% CI=[11; 19]). Participants were the most accurate when one of the surfaces was gravel (%Correct=95.4%, SD=1.17 CI=[92.5; 97.2]). Results for the two participants with LLA differed. Both individuals scored lower in comparison to unimpaired individuals on rough tile (z= -1.8 and -2.4, respectively). Discussion: The combination of “rough” and “motile” qualities (gravel) produced the highest response accuracy for both groups. While results for the participants with LLA were mixed, both demonstrated poorer scores with the rough tile sample. This suggests that people with LLA have a harder time detecting rough surfaces compared to motile surfaces, possibly due to an absence of cutaneous sensation from the prosthetic limb. Conclusion: Our findings suggest that discrimination ability depends on surface quality. Individuals with LLA may be able to discriminate between surfaces, despite sensory deficits, but at lower accuracies compared to unimpaired individuals.