Does botulinum toxin injection site determine outcome in post-stroke plantarflexion spasticity? Comparison study of two injection sites in the gastrocnemius muscle: a randomized double-blind controlled trial

Objective: To determine if botulinum toxin type A injection at the proximal 2/10 and 3/10 of calf length, where the intramuscular nerve endings of the gastrocnemius muscle are densely distributed, is more efficacious in controlling plantarflexion spasticity than injection at distant sites within the same muscle. Design: A double-blind randomized controlled trial. Settting: Two rehabilitation centres. Subjects: Forty stroke patients were randomly allocated to two groups. Group A received injection at the proximal 2/10 and 3/10 of calf length, group B at and below the midbelly of the muscle. Both groups received 200 IU of botulinum toxin A and were followed up to eight weeks. Main measures: Primary variables were the surface electromyography values recorded during plantarflexion; secondary variables were the Modified Ashworth Scale, Modified Tardieu Scale, clonus scale, 10-metre walking test, ABILOCO and Functional Ambulation Categories. Results: At baseline, the median Modified Ashworth Scale was 2.0 (range, 1+ -3.0), and there were no significant differences between the two groups in all the parameters, including spasticity. Compared to baseline, no significant differences between the two groups were detected in all the surface electromyography and clinical parameters at week 8 (P > 0.05). Both groups showed significant improvement of spasticity with a median Modified Ashworth Scale of 1+ (range, 0.0-2.0) at eight weeks. Conclusions: Botulinum toxin A injection was associated with a significant improvement from baseline to week 8 in both treatment groups, however, no significant difference between the 2 groups was observed, based on the electrophysiological and clinical parameters employed in this study.