An Exploration Into Potential Contributing Factors to Upper Limb Associated Reactions in People With Acquired Brain Injury

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<h3>Research Objectives</h3> To determine which potential contributing factors are associated with upper limb associated reaction (AR) expression in individuals with acquired brain injury (ABI). <h3>Design</h3> Cross-sectional observational study. <h3>Setting</h3> A major brain injury rehabilitation centre in Australia. <h3>Participants</h3> Forty-two participants with an adult-onset, non-progressive ABI and an AR in their hemiplegic upper limb during walking were recruited. <h3>Interventions</h3> N/A <h3>Main Outcome Measures</h3> Participants underwent three-dimensional motion analysis at self-selected walking speed to generate an AR outcome measure, quantifying upper limb kinematic deviation compared to healthy controls. Clinical assessment of potential contributing factors included: upper and lower limb hypertonicity, spasticity and strength, balance, dynamic walking stability, arm and leg function, anxiety, arm pain/discomfort, and fear of falling. <h3>Results</h3> Significant, moderate-to-strong correlations (r = 0.42 - 0.74, p < 0.05) existed between upper limb ARs and both hypertonicity and spasticity of the upper limb muscles and the knee extensors. Significant, moderate correlations to ARs (r = 0.42 - 0.59, p < 0.05) existed for balance, dynamic stability, upper limb strength, and arm function. Those participants who had hypertonicity of shoulder internal rotators, elbow, forearm, and finger flexors; spasticity of the elbow and finger flexors; knee extensor spasticity; and, reduced dynamic stability had a more severe AR (p < 0.05; effect sizes ≥ 0.80). Associated reactions were however present in the absence of positive upper motor neuron syndrome features. For example, 21% of participants had an elbow joint axis AR without elbow flexor hypertonicity and 33% without elbow flexor spasticity. <h3>Conclusions</h3> Associated reactions are complex and multi-factorial. There were several significant correlations and factors that may influence AR severity. While positive upper motor neuron syndrome features should be prioritised for clinical assessment, these factors are not prerequisites for ARs. <h3>Author(s) Disclosures</h3> There are no disclosures or conflicts to declare.