Immunocytochemical and dye distribution studies of nerves potentially desensitized by injections into the distal interphalangeal joint or the navicular bursa of horses.

The research investigated the intercommunication and nerve distribution between the distal interphalangeal (DIP) joint and the navicular bursa in horses, assessing the possibility of their desensitization through the injection of anesthetics.

Methodology

• In the procedure, 152 horse digit samples were procured post-mortem to carry out the experiment.
• Three different solutions were prepared – Evans blue dye in saline, Luxol fast blue dye with mepivicaine, and commercial latex. These were injected into the DIP joint or the navicular bursa of the collected samples.
• Following the injection, the samples were frozen and sectioned using a band saw for examination of the dye or latex distribution.

Results

• Out of 122 injections into the DIP joint, only a couple showed a communication between DIP and the navicular bursa or digital flexor tendon sheath, demonstrating a low probability of intercommunication.
• Examinations of 16 injections into the navicular bursa revealed that a majority (14) did not have a direct link with the DIP joint.
• Injections into the DIP joint resulted in the dye spreading and staining other structures such as the collateral sesamoidean ligaments, the distal sesamoidean impar ligament, the medullary cavity of the navicular bone, and faintly, the navicular bursa.
• The dye injected into the navicular bursa predominantly stained the internal lining of the bursa without any significant diffusion.

Immunocytochemical Analysis

• Immunocytochemical staining showed nerves reactive to substance P and calcitonin gene-related peptide, neurotransmitters that signal pain, in the areas that were stained by the injection in the DIP joint.

The research suggests a potential for reducing pain in the DIP joint and navicular bursa of horses. If these areas are targeted with anesthetics, it is likely to indirectly desensitize nerves contained within these structures, thus providing relief.