A simplified ultrasonography-guided approach for neurotoxin injection into the obliquus capitis inferior muscle in spasmodic torticollis

The obliquus capitis inferior (OCI) muscle may be crucially involved in generating the tremulous component of spasmodic torticollis. This study was undertaken to evaluate the efficacy of a simplified ultrasonography-guided approach of botulinum neurotoxin injection into the OCI in the management of spasmodic torticollis. Here, a novel off-plane technique of ultrasonography-guided botulinum neurotoxin injection into the OCI is demonstrated on video. We investigated its effect in five patients with tremulous torticollis with only partial response to conventional injection technique not injecting OCI. On ultrasonography the OCI and its neighboring structures (greater occipital nerve, vertebrae C1 and C2) were clearly displayed. Unlike the previously proposed approach with axial OCI imaging and in-plane medio-lateral needle insertion, we applied here an off-plane needle insertion technique. With this, the ultrasonography guidance of needle insertion was easier using the sagittal imaging plane rather than the axial plane. Compared to botulinum neurotoxin injection into more superficial neck muscles only, additional ultrasonography-guided botulinum neurotoxin injection into the OCI led to a higher benefit (self-rated improvement of cervical dystonia, p = 0.026, Mann-Whitney test), especially of the tremulous component (p = 0.007), even though the total botulinum neurotoxin dose was not changed. We conclude that selected patients with tremulous torticollis may benefit from botulinum neurotoxin injection into the OCI.