Anatomy and Ultrasound-Guided Injection of the Deep Branch of the Lateral Palmar Nerve in the Horse: A Cadaveric Study

Proximal suspensory ligament (PSL) injuries are a common cause of lameness in horses. Localization of pain in the proximal metacarpal and carpal region remains challenging. Current diagnostic analgesic techniques are not PSL-specific. The aim of this study was to investigate the nerve supply of the PSL, with particular focus on the deep branch of the lateral palmar nerve (DBLPaN), and to develop a landmark-based, ultrasound-guided injection technique targeting this nerve. Eighteen limbs from euthanized horses were dissected to describe the anatomy of the DBLPaN and branches, measuring distances from the distal margin of the accessory carpal bone (ACB) to the nerve origin and its insertion on the suspensory ligament. These findings guided development of an ultrasound-guided injection technique, which was assessed in 20 additional limbs. Considerable anatomical variability was observed, with two to six accessory branches per DBLPaN. Mean distance from the distal ACB margin to the DBLPaN origin was 2.5 cm and to the insertion on the PSL was 5.1 cm. Injections were successful in 65%, partially successful in 25%, and unsuccessful in 10% of limbs. The current study provided new detailed information regarding the anatomy of the DBLPaN and of the PSL innervation. The DBLPaN was injected with an accuracy that would be of clinical value. These findings provide a foundation for the development of more specific diagnostic analgesic techniques and warrant further in vivo investigation.