Bone and muscle properties in individuals with chronic stroke

Abstract

Background: Bone health is often compromised after stroke with greater incidence of fracture on the paretic side. Unilateral alterations to paretic muscle are also a common sequela after stroke. Although the relationship between bone integrity and muscle strength post-stroke is well-established, the association between specific muscle material changes and the mechanical strength of bone is unknown. Moreover, alterations in bone tissue properties and their clinical correlates require further study. Objectives: The main objectives of this thesis project were (1) to investigate the impact of stroke on the bone properties of the distal radius and tibia using High Resolution - peripheral Quantitative Computed Tomography (HR-pQCT), and muscle properties of the biceps brachii and the medial gastrocnemius, and (2) to identify the correlates of mechanical bone strength and muscle tissue alterations in people with chronic stroke. Methods: This was a cross-sectional project involving 64 participants with chronic stroke (age: 60.8±7.7 years, stroke duration: 5.7±3.9 years) and 64 age- and sex-matched controls. Bilateral bone parameters of the distal radius and tibia were measured using HR-pQCT. Muscle architecture, stiffness and composition as well as brachial and popliteal artery vascular outcomes were evaluated using B-mode, elastography, pulse wave and color Doppler ultrasound. Other relevant clinical and functional outcomes were also assessed. A mixed design two-way repeated measures analysis of variance (ANOVA) was used to compare within and between group differences for all bilaterally assessed variables of the upper and lower limbs (p≤0.05). Post hoc analyses involved paired t-test for within-group differences and independent t-tests for between-group differences (p≤0.017). Pearson's correlations were used to determine associations between the side-to-side difference (%SSD) in all bilaterally assessed variables (p≤0.05). Lastly, multiple regression was used to determine significant predictors of percent side-to-side difference (%SSD) in estimated failure load of the distal radius and tibia for the stroke group. Results: There was a significant side by group interaction effect for estimated failure load and all volumetric density, trabecular, and cortical bone parameters (p≤0.012) of the distal radius, with the exception of intra-cortical porosity (p=0.179). Post hoc analyses showed percent side-to-side differences in these outcomes occurred only in the stroke group. Muscle echo intensity (p=0.030), Motor Activity Log (MAL) (p=0.004), and Fugl-Meyer Motor Assessment (FMA) scores (p<0.001) were significant determinants of the percent side-to-side difference in estimated failure load of the distal radius. For the distal tibia, a significant side by group interaction effect was observed for estimated failure load (p≤0.001), cortical area and thickness (p≤0.001), and all volumetric density 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 analyses showed that the 10-meter walk test (p=0.043) and the ankle clonus score of the Composite Spasticity Scale (p=0.032) scores were significant predictors of %SSD in estimated failure load (R2=0.213). Conclusion: This study showed that bone microstructure in the paretic upper limb and bone density and cortical macrostructure in the lower limb are significantly altered on the paretic side post-stroke. Muscle morphology, disuse, motor impairment, walking speed and spasticity are important correlates of distal radius and tibia bone strength and should be the potential targets for intervention to either maintain or improve bone health after stroke.