Blocking the hoof joint and it’s effect on the rest of the foot

Important research on the effects of commonly used blocks in the localization of lameness in the horse. For decades we have made interpretations based on simple anatomy but knowing that the anesthetic can seep into surrounding structures confounding our interpretations. Here we look at blocking the distal interphalangeal joint and its effect on the rest of the hoof. Surprisingly little effect occurs on the superficial structures of the hoof following DIP analgesia. In other words, if the lameness is relieved with DIP analgesia, the problem is likely to be in the DIP joint and its related structures.
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Mechanical nociceptive assessment of the equine hoof following distal interphalangeal joint intra-articular anesthesia
PeerJ. 2020 Aug 11;8:e9469. doi: 10.7717/peerj.9469. eCollection 2020.
Authors
Bruno D Malacarne 1 , Leticia O Cota 1 , Antônio C P Neto 1 , Cahuê F R Paz 2 , Lucas A Dias 1 , Mayara G Corrêa 1 , Armando M Carvalho 1 , Rafael R Faleiros 1 3 , Andressa B S Xavier 1
Affiliations
1 Equinova Research Group -Department of Veterinary Clinics and Surgery, School of Veterinary, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
2 Centro Universitário INTA-Uninta, Sobral, Ceará, Brazil.
3 Conselho Nacional de Desenvolvimento Cientìfico e Tecnològico -CNPq, Brasília, Brazil.

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.