The effects of local anaesthetic solution in the navicular bursa of horses with lameness caused by distal interphalangeal joint pain.

Abstract

Analgesia of the palmar digital (PD) nerves has been demonstrated to cause analgesia of the distal interphalangeal (DIP) joint as well as the sole. Because the PD nerves lie in close proximity to the navicular bursa, we suspected that that analgesia of the navicular bursa would anaesthetise the PD nerves, which would result in analgesia of the DIP joint. To determine the response of horses with pain in the DIP joint to instillation of local anaesthetic solution into the navicular bursa. Lameness was induced in 6 horses by creating painful synovitis in the DIP joint of one forefoot by administering endotoxin into the joint. Horses were videorecorded while trotting, before and after induction of lameness, at three 10 min intervals after instilling 3.5 ml local anaesthetic solution into the navicular bursa and, finally, after instilling 6 ml solution into the DIP joint. Lameness scores were assigned by grading the videorecorded gaits subjectively. At the 10 and -20 min observations, median lameness scores were not significantly different from those before administration of local anaesthetic solution into the navicular bursa (P > or = 0.05), although lameness scores of 3 of 6 horses improved during this period, and the 20 min observation scores tended toward significance (P = 0.07). At the 30 min observation, and after analgesia of the DIP joint, median lameness scores were significantly improved (P < or = 0.05). These results indicate that pain arising from the DIP joint can probably be excluded as a cause of lameness, when lameness is attenuated within 10 mins by analgesia of the navicular bursa. Pain arising from the DIP joint cannot be excluded as a cause of lameness when lameness is attenuated after 20 mins after analgesia of the navicular bursa.