Can a Smartphone be used for Balance Assessment during Walking in Lower Limb Amputees?

Background: Nowadays, smartphones are equipped with an accelerometer module that can measure and record the body linear accelerations during walking. The aims of this study were: 1) reliability assessment of smartphone accelerometer for trunk accelerometry; 2) comparison of stability indices base on trunk accelerometry between the amputee and able-bodied subjects; and 3) comparison between energy storage and release (ESR) and multi-axis prosthetic feet users. Methods: Eleven below-knee amputees (5 multi-axis and 6 ESR prosthetic feet) and 11 able-bodied subjects enrolled in this comparative study. The dynamic stability was assessed using a smartphone attached to their back through an elastic belt during walking in a 6-m walkway. Also, normalized root mean squares (nRMS) of mediolateral (ML) and anteroposterior (AP) directions were calculated as stability indices. The intraclass correlation coefficient (ICC), standard error of measurement (SEM), SEM%, and Bland-Altman plots were used for reliability analysis. The Independent T-test was also used to compare the healthy and amputee subjects as well as ESR and multiaxis prosthetic feet users. The critical alpha was set at 0.05. Results: The results showed that the accelerometer has the ICC values more than 0.97 and 0.89 for test-retest and inter-session, respectively. Amputees had significantly higher trunk accelerations in ML direction compared to ablebodied subjects (P=0.023) but not in AP direction (P=0.496). Although the results were not significant between ESR and multi-axis prosthetic feet (AP P=0.16, ML P=0.44), the AP stability index was higher in ESR users (AP Multiaxis= 117.45, ESR=127.38). Conclusion: The smartphone can be used as a reliable measurement tool in clinical environments to assess the stability indices based on trunk accelerometry in transtibial amputees. More studies should be conducted to obtain more reliable results.