Effect of palmar digital perineural analgesia (as a model for “nerving”) on forelimb loading over varied surfaces at the walk and trot – a pilot study.

Overview

• This pilot study investigated how temporarily blocking sensation in the heel of horses’ front hooves affects their hoof loading patterns when walking and trotting on different ground surfaces.
• The goal was to understand changes in how the horses bear weight on their forelimbs, which has implications for treatments like nerve removal used in horses with navicular syndrome.

Background

• Navicular syndrome is a condition causing pain in the palmar (heel) region of a horse’s hoof and commonly leads to lameness.
• Palmar digital neurectomy (referred to as “nerving”) is a surgical procedure that removes sensation in the heel to provide relief but results in permanent loss of feeling.
• Palmar digital perineural analgesia involves temporarily blocking the nerves to the heel, allowing researchers to study effects of sensation loss without permanent surgery.
• Understanding how loss of sensation affects hoof loading can inform treatment decisions and rehabilitation for horses with navicular syndrome.

Objectives

• To examine how temporary loss of heel sensation affects the area of the hoof in contact with the ground (hoof area) and the force distribution during movement.
• To compare these effects while horses walked and trotted on both hard and soft surfaces.

Methods

• Three horses with minimal or no lameness (AAEP lameness scale scores 0 or 1) were selected.
• Tekscan hoof sensors embedded in glue-on shoes were fitted on the front hooves to measure hoof contact area and force.
• Each horse performed walking and trotting tests in-hand on hard and soft ground surfaces.
• Tests were conducted before (pre-blocking) and after (post-blocking) applying palmar digital nerve blocks to temporarily eliminate heel sensation.
• The study design was randomized to reduce bias from order effects.

Results

• A significant interaction between surface type and nerve-blocking status was found for both hoof area and force (P < 0.0001), indicating that the effect of blocking depended on the ground surface.
• Post-blocking, horses exhibited a greater loaded hoof area when moving over hard ground compared to pre-blocking (P = 0.008).
• Similarly, the total force exerted during movement on hard ground increased after blocking (P = 0.008).
• The heel region showed increased loading in both area and force after blocking compared to the toe region (area P < 0.0001; force P < 0.001), suggesting adjusted weight distribution.

Conclusions

• Temporary nerve blocking alters the way horses load their forelimbs, particularly increasing hoof contact area and force on hard surfaces.
• The type of ground surface plays a crucial role in these changes, which is important when considering clinical assessments or rehabilitation protocols for horses with nerve desensitization.
• These findings may inform treatment strategies for horses undergoing palmar digital neurectomy for navicular syndrome by highlighting potential changes in load bearing and the importance of surface conditions.
• Further research is necessary to assess long-term effects of permanent nerve removal (“nerving”) on forelimb loading and overall locomotion.