Innervation and nerve injections of the lumbar spine of the horse: a cadaveric study

Abstract

The distal limb innervation of the horse has been studied extensively to allow use of local anaesthetic techniques to detect the origin of pain in lameness. However, the innervation of the lumbar spine has so far been poorly described and a more precise description may assist clinicians to localise back pain in the horse. To gain better knowledge of the innervation of the lumbar spine and identify salient anatomical features that might be used for diagnostic and therapeutic ultrasound guided injections. The spines of 8 mature horses were dissected. Branches of the dorsal rami were followed and their anatomical relationship, with articular facets, interspinous structures and muscles, noted. The spines of 3 other horses were sectioned transversely and dissected to identify ultrasonographic landmarks of the nerves. Six other spines were used to assess the accuracy of ultrasound guided injections of the nerves with blue dye. Gross dissections confirmed the dual segmental innervation of the articular facets. Each lumbar articular facet of 2 lumbar vertebrae was innervated by the medial branch of the dorsal ramus exiting from the intervertebral foramen between those vertebrae, but also by the branch originating of the dorsal ramus cranial to it. The medial branch divided into 2 nerves before exiting the intertransverse space and has salient anatomical landmarks which could be identified ultrasonographically. The ultrasound guided injection technique appeared to be of an accuracy that would be clinically useful. The results identified that the salient anatomical features of the medial branch of the dorsal ramus, as described in the present study, can be used as landmarks for reliable ultrasound-guided injection. This study has a clear clinical relevance for development of diagnostic and therapeutic injection techniques of the lumbar spine in the horse.