Implications of the neuroanatomy of the equine thoracolumbar vertebral column with regional anaesthesia and complications following desmotomy of the interspinous ligament.
Authors: Derham Ann M, Schumacher Jim, O' Leary John M, Kelly Ger, Hahn Caroline N
Journal: Equine veterinary journal
Summary
# Editorial Summary: Neuroanatomy and Complications in Equine Thoracolumbar Surgery Overriding dorsal spinous processes remain a frequent diagnosis in poor-performing horses, with surgical correction traditionally reporting excellent cosmetic outcomes; however, a recently documented complication of contralateral epaxial muscle atrophy following interspinous ligament desmotomy suggests that surgical technique may inadvertently damage the nerve supply to the longissimus dorsi muscle, particularly when instruments are placed too far lateral to the midline. Through a comprehensive literature review, Derham and colleagues identified a critical gap in equine neuroanatomical knowledge, proposing that intermediate branches of the dorsal spinal nerves are vulnerable during desmotomy—a risk largely unrecognised because detailed equine-specific neural anatomy remains sparse compared with human and companion animal literature. This anatomical deficit extends beyond surgical applications: the highly variable techniques used for diagnostic local anaesthesia of the equine back lack a sound neuroanatomical foundation, potentially explaining why pain-blocking procedures inconsistently improve performance or gait abnormalities attributed to back pain. For practitioners, these findings underscore the importance of precise midline technique during interspinous ligament procedures and suggest that inconsistent responses to diagnostic local anaesthesia may reflect anatomical variation rather than diagnostic failure, highlighting an urgent need for detailed equine thoracolumbar neuroanatomical research to guide both surgical and diagnostic protocols.
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Practical Takeaways
- •Surgeons performing interspinous ligament desmotomy must be cautious to keep instruments strictly on midline to avoid transecting dorsal spinal nerve branches, which causes permanent muscle atrophy on the opposite side
- •Local anaesthesia for back pain diagnosis is unreliable in horses due to poor anatomical knowledge; inconsistent responses between horses may reflect anatomical variation or nerve distribution differences rather than diagnostic failure
- •When horses with suspected back pain show poor response to regional anaesthesia or develop post-operative muscle wasting, consider nerve injury as a possible cause and seek detailed anatomical imaging or specialist consultation
Key Findings
- •Neurogenic atrophy of contralateral epaxial muscle is a previously unreported complication following interspinous ligament desmotomy, potentially caused by transection of intermediate branches of the dorsal spinal nerve supplying m. longissimus
- •Literature on equine thoracolumbar neuroanatomy is severely lacking compared to humans and companion animals, with most knowledge extrapolated from other species
- •Wide variation in local anaesthesia techniques for equine back pain localization exists, which may explain inconsistent therapeutic responses between individual horses
- •Current understanding of neural anatomy in the equine back is insufficient to support safe surgical techniques and effective diagnostic local anaesthesia protocols