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

Abstract

Navicular syndrome is one of the most common causes of lameness in horses characterized by inflammation and degeneration of the navicular bone with or without soft tissue involvement. Palmar digital neurectomy or “nerving” removes the sensation to the heel region of the hoof and allows horses with navicular syndrome to still compete without pain. This method does not heal the disease but may mask symptoms. Analgesia or “blocking” of the palmar digital nerves results in temporary loss of sensation. The purpose of this pilot study was to examine the effect of loss of sensation in the heel (as a result of blocking) on the forelimb area and force while tracking on soft and hard ground at the walk and trot. It was hypothesized that soft ground would result in greater normal force and pressure distribution of the hoof and analgesia of the palmar digital nerves would result in greater loading on all surfaces at the walk and trot. Three mature stock-type horses determined to be without lameness were fitted to Tekscan Hoof Sensors via glue-on shoes on the front hooves. Each horse was randomly assigned the order for each test which included walking and trotting on a hard (rubber alleyway) and soft surface (arena clay). Horses completed the same exercise sessions pre- and post-nerve blocking examining hoof normal force, loaded area, and stride duration. After the pre-blocking runs, horses completed the same tests but underwent palmar digital analgesia or “blocking” by a veterinarian. Analysis was performed in SAS 9.4 with a GLIMMIX procedure: fixed effects of gait, run, ground, step, block, and leg, with interactions. Interaction of ground and blocking status was significant for area (P < 0.0001), with post-blocking having greater loaded area than pre-blocking while tracking on hard ground (P = 0.008), but no difference between pre- and post-blocking on soft ground (P = 0.94). The same interaction was found significant for force (ground × block P < 0.0001), with force while tracking over hard ground being greater post-blocking than pre-blocking (P = 0.008), but not different while tracking over soft ground (P = 0.20). Interaction of gait and blocking status was not significant for area (P = 0.41) or force (P = 0.10). Stride duration was greater pre-blocking than post-blocking (P = 0.0017). Findings from this pilot study show that temporary blocking impacts forelimb loading characteristics and that ground may be an important factor in tracking for horses with removed sensation to the forelimb heel and provides support for further exploration into the long-term effects of nerving.