The neurovascular bundle of the equine distal cannon can dynamically vary with limb position, and this can affect the performance of low 4- or 6-point block. This study aims to identify and describe the anatomical position and variations of the lateral and medial palmar/plantar nerve at the metacarpal/metatarsal distal level in horses by ultrasonography. Eight mares underwent ultrasound examination on the lateral and medial palmar/plantar sides of the metacarpus/metatarsus. Images were obtained for measurements of the cross-sectional area of the nerve, distances between the nerve and the skin surface, branch of the suspensory ligament (SL), deep digital flexor tendon (DDFT) and superficial digital flexor tendon (SDFT) with limbs supported and elevated. The distance to the skin for forelimbs was higher on the lateral side when the limb was elevated (p < 0.001). The comparisons between supported and elevated limbs on the same side showed longer distances to the skin with the limb supported on the medial side (p < 0.001). Hindlimbs showed longer distances to the skin with the limb supported on the medial face (p = 0.027). The anatomical position of palmar/plantar nerves was similar between the lateral and medial sides of the limb, generally being in contact with the dorsal edge of DDFT. The strategy of elevating the limb during the injection of the low 4- or 6-point block can lead to a higher risk of puncture of the digital sheath.
Keywords: Perineural block; diagnosis; lameness; ultrasonography.
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