A COMPARISON OF RESPONSES TO ANALGESIA OF THE NAVICULAR BURSA AND INTRAARTICULAR ANALGESIA OF THE DISTAL INTERPHALANGEAL JOINT IN 59 HORSES

Analgesia of the distal interphalangeal (DIP) joint and of the navicular bursa was performed independently in the lame or lamer forelimb of 59 horses, in which lameness was significantly improved by perineural analgesia of either the palmar digital or palmar (abaxial sesamoid) nerves. In 3 horses no improvement was detected. Lameness was improved by analgesia of the DIP joint but there was no response to analgesia of the navicular bursa in 3 horses. In 12 horses, lameness was improved by analgesia of the navicular bursa but intra-articular analgesia resulted in no change. Forty-one horses responded both to analgesia of the navicular bursa and intra-articular analgesia of the DIP joint. Synovial fluid was retrieved from all DIP joints but from only one navicular bursa. It is suggested that a positive response to analgesia of the DIP joint does not necessarily imply that pain arises from the joint per se, but a positive response to intra-bursal analgesia probably reflects pathology of the bursa per se, the navicular bone and/or supporting ligaments and/or the DDFT. Radiographic abnormalities of the navicular bone in the lame or lamer limb were detected in 35 horses, all of which showed some response to analgesia of the navicular bursa. In 25 of these horses (71%) changes were only identifiable in the palmaroproximal-palmarodistal oblique views. There was a higher incidence of radiographic abnormalities of the navicular bone in horses in which the response to intra-articular analgesia of the DIP joint was similar (70%) to, or greater (71%) than analgesia of the navicular bursa, compared with the groups in which there was no response (58%) or a lesser response (62%) to intra-articular analgesia. The front feet of 6 horses were examined post mortem. All horses had pathological abnormalities of the flexor surface of the navicular bone of the tame or lamer limb and in 5 there was associated fibre damage of the opposing deep digital flexor tendon. No abnormalities of the DIP joint were identified. We suggest that, when possible, if foot pain is suspected, the following analgesic techniques should be performed in sequence, but on different occasions: (1) perineural analgesia of the palmar digital (and when necessary palmar [abaxial sesamoid]) nerves; (2) analgesia of the DIP joint; and (3) analgesia of the navicular bursa.