Function of the ramus communicans of the medial and lateral palmar nerves of the horse.

This study investigates the role of the ramus communicans, a nerve branch connecting the medial and lateral palmar nerves in horses. The research shows that blocking only one of these nerves does not completely resolve lameness, and therefore both should be anesthetised to achieve optimal results.

Research Objective

• The primary aim of this research was to understand the workings of the ramus communicans, a neural connection between the medial and lateral palmar nerves in horses. Specifically, they wanted to determine the direction of sensory impulses through this neural branch.

Methods

• The researchers induced pain in 6 horses’ thoracic foot by applying a set-screw pressure to either the medial or lateral aspect of the sole.
• Following this, they administered local anaesthetic to the palmar nerve on the side of the foot where pain had been induced. This was done proximal to the ramus communicans.
• The impact of the anaesthesia injections on lameness was measured both by using an inertial sensor-based motion analysis system (Lameness Locator) and a subjective scored grading system.
• After these initial steps, the researchers injected anaesthetic adjacent to the ramus communicans to see its effect on the residual lameness.

Results

• The results indicated that anaesthetising the palmar nerve proximal to the ramus communicans did not entirely resolve lameness when pain originated from either side of the foot. However, administering anaesthetic to the ramus communicans greatly reduced or even resolved the lameness.

Conclusion

• This study suggests that sensory fibres pass in both directions through the ramus communicans, which connects the medial and lateral palmar nerves in horses. Consequently, when administering a low palmar nerve block, both palmar nerves should be anaesthetised distally to the ramus communicans. This will prevent leaving non-desensitised sensory nerve fibres, and thus, potentially more effective pain management.
• Alternatively, the study suggests that one can deposit local anaesthetic adjacent to the ramus communicans when anaesthetising the palmar nerves for a more complete pain management strategy.