Test-retest reliability and minimal detectable change of ankle kinematics and spatiotemporal parameters in MS population

Background: Many people with multiple sclerosis (pwMS) experience walking impairments often including foot drop, evident as either reduced dorsiflexion at initial contact and/or at the swing phase of the gait cycle. To measure even subtle differences in ankle kinematics, 3D gait analysis is considered a 'gold' standard. However, the psychometric properties of ankle kinematics in the MS population have not yet been examined.

Objective: The aim of the study was to examine test-retest relative and absolute reliability of sagittal ankle kinematics and spatiotemporal parameters in two groups of pwMS with different levels of walking impairment.

Methods: Two groups of pwMS underwent 3D gait analysis on two occasions 7-14 days apart. Group A consisted of 21 (14 female) people with Expanded Disability Status Scale (EDSS) 1-3.5 and group B consisted of 28 participants (14 female) with EDSS 4-6. The Intraclass Correlation Coefficient (ICC_2,2), standard error of measurement (SEM) and minimal detectable change (MDC_95%) were calculated for peak dorsiflexion (DF) in swing, ankle angle at initial contact (IC), gait profile score (GPS), walking speed, cadence and step length.

Results: Both groups presented 'excellent' ICC values (>0.75) for DF in swing, IC and step length of most and least affected limbs, walking speed and cadence, with GPS for both limbs exhibiting 'fair' to 'good' ICCs (0.489-0.698). The MDC_95% values for all ankle kinematic parameters in group A were lower (1.9°-4.2°) than those in group B (2.2°-7.7°).

Conclusion: The present results suggest that ankle kinematic and spatiotemporal parameters derived from 3D gait analysis are reliable outcome measures to be used in the MS population. Further, this study provides indices of reliability that can be applied to both clinical decision making and in the design of studies aimed at treating foot drop in people with MS.