Sensory innervation of the navicular bone and bursa in the foal.

The research is a study of how the navicular bone, its ligaments, and the navicular bursa in newborn horses are innervated by nerves that are sensitive to substance P and calcitonin gene-related peptide, in relation to potential anesthesia injections.

Study Overview

• The study examined the sensory innervation – the supply of nerves – in the navicular bone (the distal sesamoid bone in the horse’s hoof), its suspensory ligaments (collateral sesamoidean ligament or CSL, and distal sesamoidean impar ligament or DS-impar) and the navicular bursa (a small fluid-filled sac between the tendon and the bone) of neonatal foals.
• The research was conducted using immunocytochemistry, a laboratory technique that visually detects a particular substance within a cell using a specific antibody that binds to it.
• Anti-sera against substance P (SP) and human calcitonin gene-related peptide (CGRP) were used during the experiment. These are peptides released in response to nerve stimulation and are involved in transmitting pain signals.

Findings

• Innervations were discovered in both the navicular bone and bursa. They were located within the CSL and appeared to reach the surface lining of the navicular bursa.
• The nerves seemed to enter these structures from the outer regions of the foal’s foot.
• Substance P and the human Calcitonin gene-related peptide were also found in the deep digital flexor tendon (DDf) along the back edge of the navicular bursa and in the DS-impar ligament.
• The research showed higher nerve fibre concentration in the upper part of the CSL along the distal interphalangeal joint than was observed on the rear side of the CSL along the navicular bursa.

Anatomical Distributions

• In the navicular bone, the identified peptides were observed to supply the cartilage canals, a crucial system for cartilage nutrition and the potential transmission of systemic diseases.
• As per the relative densities of detected peptide-like nerve fibres, the CSL dorsally and the DS-impar ligament displayed the highest amounts, followed by the navicular bone, the backside of the CSL, and then the deep digital flexor tendon neighbouring the navicular bursa.

Implications

• The results are crucial because they provide insights into the innervation of structures within the foal’s foot. This knowledge may lead to a better understanding of the potential pain pathways in foot diseases such as navicular syndrome.
• In addition, the study results might affect how local anaesthetic injections into the navicular bursa are administered, as they reveal the possible diffusion and effect pathways of the drugs.