Reliability and Validity of Continuous Inter-limb Stability

There is currently no valid or reliable biomechanical variable available to objectively measure the continuous stability of Veterans with lower limb loss. However, continuous inter-limb stability represents a potential target to improve whole-body dynamics, as it is an important measure of functional mobility in individuals with lower limb loss. Determining the reliability and validity of this measure is critical for limb loss care teams since these features are fundamental to interpretability and assessment of this parameter. Unlike traditional clinical assessments of stability that focus on the time of task execution, Relative Phase (RP) analysis, which is a novel methodology that can be used to evaluate continuous stability, uses both space and time within one outcome variable. While previous literature supports the use of continuous stability for mobility challenged populations, such as individuals with limb loss, it has yet to be shown reliable and valid for such populations. Therefore, the first aim of this study is to identify the reliability and validity of continuous inter-limb stability in individuals with transtibial limb loss (TLL) using RP analysis. For this parameter to be used clinically, it is vital to provide rehabilitation specialists the ability to assess continuous stability within the clinical setting. To date, this factor of functional mobility has only been evaluated using 3-dimensional (3-D) motion capture, which is costly and inaccessible to most rehabilitation clinics. Therefore, the second aim of this study is to identify the strength of the association between wearable technology (using inertial measurement units) and 3-D motion capture system for evaluation of continuous interlimb stability of individuals with TLL. The central hypothesis is that continuous stability evaluated using RP analysis will be a reliable and valid measure of functional mobility for Veterans with TLL and that data captured via wearable technology will be strongly associated with 3-D analysis. Twenty Veterans with TLL will be recruited and enrolled via the Prosthetic or Physical Medicine Departments at Veterans Affairs New York Harbor Healthcare System, where all data collection will occur. To measure test re-test reliability, participants will undergo 3 sessions of 3-D gait analysis while walking at a moderate speed (1.3m/s) until 15 walking cycles are captured, with 1 day between sessions. RP analysis will be used to identify the continuous inter-limb stability of gait patterns. Participants will be fit with wearable technology and data will be collected concurrently. To measure convergent validity, participants will perform functional outcome measures including the Timed Up and Go test, 6 Minute Walk Test, Hill and Stair Assessment Indexes, and Amputee Mobility Predictor. Data from 40 participants are required to appropriately power the analysis of convergent validity. To achieve this power, data from 20 participants collected during a previously funded Department of Defense study will be leveraged and added to the data of the 20 participants collected during the proposed study. This is possible due to identical data collection techniques in both studies. To assess the level of agreement between the data obtained from the 3 sessions, Intraclass Correlation Coefficients will be calculated for each variable, in addition to Cohen's kappa statistics and Pearson correlation coefficients. To assess convergent validity, Pearson and Spearman rank correlation coefficients will quantify the strength and direction of the relationships between the outcome measures and continuous stability. Substantiating the use of continuous stability in Veterans with TLL will afford healthcare providers information necessary to accurately detect and appropriately address stability deficiencies, which is critical since superior stability is linked to increased physical activity leading to an enhanced overall quality of life of Veterans with limb loss. Verifying the reliability and validity of this parameter will lead to its confident application for future studies focused on effectiveness, optimization, and rehabilitation.