Botulinum Toxin A for Elbow Flexor Spasticity: A Non-Randomized Observational Study of Muscle-Specific Injection Strategies

<b>Introduction:</b> Elbow flexor spasticity is a common and debilitating consequence of stroke, significantly impacting patients' quality of life. Botulinum toxin A (BoNT-A) injections have emerged as an effective treatment, but the optimal muscle selection strategy remains unclear. This study investigates the impact of different BoNT-A injection strategies targeting specific elbow flexor muscles in post-stroke patients. <b>Materials and Methods</b>: A non-randomized observational study was conducted on 52 participants with upper limb spasticity (pattern IV) following a stroke. Participants were divided into three groups based on the elbow flexor muscles injected with BoNT-A: biceps brachii (<i>n</i> = 15), brachialis (<i>n</i> = 9), and brachialis plus brachioradialis (<i>n</i> = 28). Assessments included spasticity angle, paresis angle, and active supination range of motion (ROM) measured using the Tardieu Scale and goniometry at baseline and at 4-week follow-up. Non-parametric statistical analyses were employed to compare outcomes between groups. Results: While all groups showed a general trend of decreased spasticity and improved motor control, analysis revealed statistically significant differences across the groups at baseline. The brachialis plus brachioradialis group demonstrated the most substantial improvement in paresis angle and active supination ROM. Notably, this group also exhibited greater capacity for the improvement of the paresis angle. The biceps brachii group showed comparable improvements in the paresis angle and the greatest effect on improving passive extension at slow velocity with increasing stroke onset but required higher pronator teres BoNT-A doses overall. <b>Discussion</b>: These findings suggest that individualized muscle selection strategies are crucial in BoNT-A treatment for elbow flexor spasticity. The superior outcomes observed in the brachialis plus brachioradialis group may be attributed to the synergistic action of these muscles in elbow flexion and forearm positioning. The higher pronator teres BoNT-A doses required in the biceps brachii group may reflect compensatory mechanisms or differences in muscle fiber recruitment patterns. <b>Conclusions</b>: Combining brachialis and brachioradialis muscles in BoNT-A injections appears to offer superior benefits for supination and motor control in post-stroke patients with elbow flexor spasticity, particularly those with significant elbow flexion and pronation.