The diagnostic nerve block of the sesamoidean nerve: desensitized structures and possible clinical applications.

The sesamoidean nerve branches from the palmar nerve and runs towards the proximal sesamoid bone. To study the structures innervated by this nerve, a technique for blocking it was developed. The effect of this nerve block was determined in ponies with an induced lameness located in the lateral proximal sesamoid bone (5 ponies) or in the distal part of the lateral branch of the suspensory ligament (5 ponies), and in 10 horses with clinical sesamoidosis. A lameness provoked by the implantation of an expansion plug in the proximal sesamoid bone could, to a large extent, be anaesthetized by a sesamoidean nerve block. However, lameness due to a local tendonitis in the lateral branch of the suspensory ligament, was only partially eliminated by a sesamoidean nerve block. In horses with sesamoidosis the lameness improved, on average, by about 30%. It is concluded that the sesamoidean nerve contains sensory fibres that innervate the proximal sesamoid bone. The sesamoidean nerve block is highly specific for pain originating from the proximal sesamoid bone including the adjacent distal part of the extensor branch of the suspensory ligament. In horses suffering from sesamoidosis the main source of pain appears not to be located in the proximal sesamoid bone. The specificity of the sesamoidean nerve block makes it a useful technique for differentiating the site of a lameness located in the fetlock area.