GAIT SPEED AND SPASTICITY AS PREDICTORS OF ESTIMATED FAILURE LOAD IN THE DISTAL TIBIA OF INDIVIDUALS WITH CHRONIC STROKE

T. Miller¹, C.S. Tsang¹, V.W. Hung², L. Qin², M. Ying³, M.Y. Pang¹

Background: Lower extremity bone health is often compromised after stroke. Altered macro- and microstructural properties of bone tissue may have important neuromuscular and functional correlates.

Purpose: (1) To explore the influence of stroke on distal tibia bone properties and,
(2) to identify the clinical correlates of estimated failure load of the distal tibia in people with chronic stroke.

Methods: 64 individuals with chronic stroke (age: 60.8±7.7 years, stroke duration: 5.7±3.9 years) and 64 age- and sex-matched controls participated in this cross sectional study. Bone parameters of the distal tibia were measured bilaterally using High Resolution – peripheral Quantitative Computed Tomography (HR-pQCT). Muscle architecture, stiffness and echo intensity of the medial gastrocnemius muscle and blood flow of the tibial artery were assessed with ultrasound. Clinically relevant measures were assessed using the 10 Meter Walk Test (10MWT), Fugl-Meyer Motor Assessment (FMA), Brief BESTest and Composite Spasticity Scale (CSS). General level of physical activity was assessed with the Physical Activity Scale for the Elderly (PASE). Statistical analyses involved the use of mixed design two-way repeated measures analysis of variance (ANOVA) to compare within and between group differences for all bilaterally assessed HR-pQCT, ultrasound and impairment/functional variables [within-subject factor: side (paretic (for stroke group) or non-dominant (for control group) vs non-paretic (for stroke group) or dominant (for control group)), between-subject factor: group (stroke vs control)]. Post hoc analyses involved paired t-test for within-group differences and independent t-tests for between-group differences. Pearson’s correlations were used to determine the association between side-to-side difference (%SSD) in estimated failure load of the tibia and potential predictor variables. Hierarchical multiple regression was then used to determine the significant predictors of %SSD in estimated failure load of the tibia in the chronic stroke group.

Results: A significant side-group interaction effect was observed for the estimated failure load (p≤0.001), cortical area and thickness (p≤0.001), and all densitometric parameters (p≤0.009). Post hoc analyses revealed significant side-to-side differences in these parameters for the stroke group but not for controls. Multivariate regression analysis showed that the 10MWT (p=0.043) and the ankle clonus score of the CSS (p=0.032) scores were significant predictors of %SSD in estimated failure load (R²=0.213), after accounting for the effects of age, sex, duration from stroke onset, and physical activity level.

Conclusion(s): This study used HR-pQCT to assess lower limb bone properties in individuals with chronic stroke. The paretic distal tibia showed compromised bone density and cortical macrostructure, contributing to a comparatively lower estimated failure load than that of the non-paretic tibia. Gait speed and spasticity appear to be strong correlates of bone strength in the distal tibia.

Implications: Future intervention strategies with the aim of preserving or improving bone strength should incorporate elements which target walking function and spasticity.

Funding, acknowledgements: Funding provided by Hong Kong Polytechnic University (Grants RL27 and RUNV) and the Research Grants Council (General Research Fund: 151031/18M)

Keywords: distal tibia, estimated failure load, stroke

Topic: Neurology: stroke

Did this work require ethics approval? Yes

Institution: Hong Kong Polytechnic University

Committee: Human Subjects Ethics Sub-Committee of the Hong Kong Polytechnic University

Ethics number: HSEARS20171212003 and CREC: 2017-711