T. Miller1, J. Ng1, R. Chung1, M. Ying2, M.Y. Pang1
1Hong Kong Polytechnic University, Rehabilitation Sciences, Hong Kong, Hong Kong, 2Hong Kong Polytechnic University, Health Technology and Informatics, Hong Kong, Hong Kong

Background: Upper limb motor impairments and limitations in the ability to perform activities of daily living are common after stroke. Previous research using extended field-of-view ultrasound has shown the paretic biceps brachii (BB) undergoes considerable structural changes. The degree to which unilateral change in muscle structure affects post-stroke motor function is unknown.

Purpose: To compare the difference in BB muscle architecture between paretic and non-paretic sides in individuals with chronic stroke and healthy controls, and (2) to examine the association between ultrasound measures and clinical assessments of post-stroke impairment and function.

Methods: A total of 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. Bilateral muscle fascicle length (FL), cross sectional area (CSA), echo intensity (EI), and shear modulus (SM) were evaluated using diagnostic ultrasound. Using a standardized musculoskeletal preset coupled with a 4-15MHz linear array transducer, SM and EI were measured with elastography and B-mode, respectively. Muscle FL and CSA images were captured using a panoramic function during acquisition. Other outcomes included elbow flexor isometric peak torque (IPT) and Motor Activity Log (MAL) scale. A mixed design two-way repeated measures analysis of variance [within-subject factor: side, between-subject factor: group] was performed for each ultrasound parameter and IPT, followed by post-hoc analysis as necessary. A path analysis was conducted to explore the relationship between ultrasound variables, strength and usage of the paretic upper limb in daily activities (MAL).

Results: A significant side by group interaction effect was observed for FL, CSA, EI and IPT (p≤0.001), with greater percent side-to-side difference observed for the stroke group than control group (p≤0.01). The results showed both IPT and SM to be significant predictors of MAL (R2=0.172). Predictors of IPT were FL, CSA, and EI (R2=0.346), while predictors of SM were FL and EI (R2=0.128). The path analysis indicated an excellent model fit (χ2=3.648, degrees of freedom=4, probability level=0.456, comparative fit index (CFI)=1.000, root mean square error of approximation (RMSEA)=0.000), with FL (β=-0.367) being the largest direct contributor to SM, CSA (β=0.371) being the largest for IPT, and IPT (β=0.351) being the largest for MAL.

Conclusion(s): Individuals with chronic stroke showed significantly different muscle structural characteristics than controls. Reduced mass (CSA), compositional changes (EI), and shortened FL of paretic muscles demonstrated an indirect effect on paretic upper limb disuse (MAL) potentially moderated by their direct effects on muscle weakness (IPT) and stiffness (SM).

Implications: In addition to conventional strength training, exercises to increase muscle length and reduce stiffness may also be important components of post-stroke rehabilitation programs aimed at improving the usage of the paretic upper limb in daily activities.

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

Keywords: musculoskeletal ultrasound, stroke, path analysis

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

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