Mechanical nociceptive assessment of the equine hoof following distal interphalangeal joint intra-articular anesthesia

Abstract

Background With the hypothesis that equine dorsal lamellar tissue can be desensitized by anesthesia injection into distal interphalangeal joint (DIPJ), the objective was to assess the mechanical nociceptive threshold of hoof dorsal lamellae following intra-articular (IA) administration of lidocaine into this joint. Methods The DIPJ of the forelimbs of six adult healthy horses were injected with either 5 mL of lidocaine, or 5 mL of lactated Ringer’s solution. Treatments were randomly distributed, with each forelimb undergoing a single treatment. The hooves were evaluated pre- and post-injection at pre-selected times over 4 h, using a pressure algometry model. Mechanical nociceptive thresholds (MNTs) were recorded for the sole (dorsal, palmarolateral, and palmaromedial regions), coronary band (medial, lateral, and dorsal regions), heel bulbs (medial and lateral), and dorsal lamellar region (2 cm and 4 cm distal to the coronary band). The MNT means were compared over time using the Friedman test and between treatments using the Wilcoxon signed-rank test, with values of P < 0.05 considered statistically significant. Results There were no differences between treatments for any region of the hoof during the evaluation period. However, MNT values indicating analgesia were recorded in the dorsal lamellar region in 50% of hooves following adminstration of lidocaine into the DIPJ. Conclusion The administration of 5 mL of lidocaine into the DIPJ does not significantly increase the mechanical nociceptive threshold of the equine hoof.

Pressure Algometry for the Detection of Mechanical Nociceptive Thresholds in Horses

“…Mechanoreceptors often become more responsive to nociceptive stimuli in the presence of heat and chemical mediators. Over the last decade, there have been numerous applications of using pressure algometry to measure MNTs in horses [18][19][20][21][22]. There is a critical need to establish normative values within different body regions and to develop standardized methods of testing MNTs.…”

“…Epidural morphine [32] Epidural ropivacaine [33] Low-4-point block [34] Digital flexor tendon sheath [35] Distal interphalangeal joint [22] Palmar digital nerves [36] Response to therapy Chiropractic [37] Chiropractic, low-level laser therapy [38] Chiropractic, massage, phenylbutazone [39] Static magnetic blanket [40] Pulsed electromagnetic therapy blanket [41] Extracorporeal shockwave therapy [42] Tail traction [21] Sublingual detomidine [43]…”

“…Limb-mounted devices can either use a pressure cuff or a pneumatically-driven pin to apply noxious stimuli and have the benefit of more controlled force application without the presence or cues associated with an operator in the immediate vicinity of the animal [15]. Some studies have used blindfolds in horses to limit environmental distractions and the visual perception of the applied device [22]. Limb-mounted devices seem to be the most preferred system for pharmacodynamic investigations of analgesic agents [4,45,46].…”

“…Round-tipped probes have been reported to produce lower MNTs than flat-ended probes [15]. Other shapes such as cone tips have been used in the hoof region to test nociceptive thresholds where higher pressures might be indicated in highly keratinized tissues [22,36].…”

“…In an effort to keep horses calm during the MNT testing, several researchers have acclimated horses to the testing environment or have kept them in their own natural environment to avoid conditioned fear or pain responses [27]. To limit environmental distractions and the visual perception of the algometer being applied, a blindfold has been applied to horses during MNT testing [22]. As horses are socially bound to living in herds, some researchers test MNTs in the company of another restrained horse to avoid stress and anxiety related to social isolation, which have the potential to negatively influence MNTs [15].…”