Comparison of lameness scores after a low 4‐point nerve block to lameness scores after additional desensitisation of the dorsal metatarsal nerves in horses with experimentally induced pain in the metatarsophalangeal joint

Anatomical position of the palmar/plantar nerves at the metacarpal/metatarsal distal level in horses: An in vivo study by means of ultrasonography

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.

Diffusion of dye after perineural injection of the palmar/plantar nerves in two different sites in horses: an ex-vivo study

This study aimed to evaluate the distribution of dye at two perineural injection sites of the palmar/plantar nerves and describe their anatomical variations of positioning at the level of the distal metacarpus/metatarsus in horses. Two ml of 1% methylene blue solution was injected in 24 limbs (12 forelimbs and 12 hindlimbs) of horse cadavers at two different points: Group 1: between the branch of the suspensory ligament and deep digital flexor tendon, and Group 2: between the deep and superficial digital flexor tendons. This was followed by dissection and evaluation of the solution diffusion. A photographic record and description of the anatomical position of the palmar/plantar nerve were performed. A comparison of diffusion directions in each portion (medial or lateral) between groups showed no statistical difference (P > 0.05), except in the dorsal direction on the medial portion of hindlimbs, which was higher in Group 2 (P = 0.025). The digital flexor tendon sheath was inadvertently injected four times into the forelimbs of Group 2. Both injection sites offered good dye contact with the palmar/plantar nerves, with the position between the deep digital flexor tendon and suspensory ligament branch having a higher contact area, regardless of the limb portion. The anatomical position of the palmar/plantar nerve in the cadaver specimens was similar between the same limb portions.