Reproducibility and discriminant validity of two clinically feasible measurement methods to obtain coronal plane gait kinematics in participants with a lower extremity amputation

INTRODUCTION: Measuring coronal plane gait kinematics of the pelvis and trunk during rehabilitation of participants with a lower extremity amputation is important to detect asymmetries in gait which are hypothesised as associated with secondary complaints. The aim of this study was to test the reproducibility and discriminant validity of a three-dimensional (3-D; inertial measurement units) and a two-dimensional (2-D; video-based) system. METHODS: We tested the test-retest and inter-rater reproducibility of both systems and the 2-D system, respectively, in participants with a lower extremity amputation (group 1) and healthy subjects (group 2). The discriminant validity was determined with a within-group comparison for the 3-D system and with a between-group comparison for both systems. RESULTS: Both system showed to be test-retest reliable, both in group 1 (2-D system: ICC3.1(agreement) 0.52–0.83; 3-D system: ICC3.1(agreement) 0.81–0.95) and in group 2 (3-D system: ICC3.1(agreement) 0.33–0.92; 2-D system: ICC3.1(agreement) 0.54–0.95). The 2-D system was also inter-rater reliable (group 1: ICC2.1(agreement) 0.80–0.92; group 2: ICC2.1(agreement) 0.39–0.90). The within-group comparison of the 3-D system revealed a statistically significant asymmetry of 0.4°-0.5° in group 1 and no statistically significant asymmetry in group 2. The between-group comparison revealed that the maximum amplitude towards the residual limb (MARL) in the low back (3-D system) and the (residual) limb—trunk angle (2-D system) were significantly larger with a mean difference of 1.2° and 6.4°, respectively, than the maximum amplitude of healthy subjects. However, these average differences were smaller than the smallest detectable change (SDC) of group 1 for both the MARL (SDC(agreement): 1.5°) and the residual limb—trunk angle (SDC(agreement): 6.7°-7.6°). CONCLUSION: The 3-D and 2-D systems tested in this study were not sensitive enough to detect real differences within and between participants with a lower extremity amputation and healthy subjects although promising reproducibility parameters for some of the outcome measures.