Botulinum toxin injection for hemiplegic shoulder pain: Do we know enough yet?

Abstract

In patients with spastic hemiplegia, botulinum toxin A (BoNTA) injection into the subscapularis (SB) has been shown to decrease shoulder pain and increase range of motion (Unlu et al., 2010; Yelnik et al., 2007). The intramuscular innervation pattern of SB has not been well studied, but could provide insight into neuromuscular partitioning, enabling the development of an optimal injection approach that enhances the efficacy of BoNTA. The purpose of this study is to document the extra‐ and intramuscular innervation patterns of SB throughout the muscle volume to identify neuromuscular partitions. Forty‐five formalin embalmed cadaveric specimens were used in this study. Extraand intramuscular innervation patterns of SB were documented using digitization and 3D modelling (n=7), and dissection and photography (n=38). Innervation patterns throughout the muscle volume were analyzed. The number of extramuscular branches (2–5) were correlated with the four identified intramuscular innervation patterns, partitioning the muscle into two parts (superior and inferior; n=11) or three parts (superior, middle and inferior; n=34). Due to the presence of neuromuscular partitions, injection in multiple locations may be required to achieve maximal effect. Future studies are needed to determine whether the number of partitions injected correlates with clinical outcomes.