Even though analgesia of the DIP joint results in analgesia of the navicular bursa,9
analgesia of the navicular bursa does not result in analgesia of the DIP joint.14,15
Analgesia of the navicular bursa may help to differentiate pain associated with
disease of the DIP joint from pain associated with disease of the navicular bone and
associated structures. Pain arising from the DIP joint can likely be excluded as a
cause of lameness when lameness is attenuated within 10 minutes by analgesia of
the navicular bursa.15
One possible explanation for the observation that analgesia of the DIP joint causes
analgesia of the navicular bursa but analgesia of the navicular bursa does not cause
analgesia of the DIP joint is that the site of direct contact between the palmar pouch
of the DIP joint and the palmar digital nerves is located proximal to the origin of the
deep branches that innervate the DIP joint and the navicular bursa, whereas the site
of direct contact between the navicular bursa and the palmar digital nerves is located
distal to these branches.
In addition to experimental findings concerning the effect of analgesia of the
navicular bursa, clinical observations indicate that a positive response to intraarticular analgesia of the DIP joint and a negative response to intra-bursal analgesia
of the navicular bursa indicate pain within the DIP joint as the cause of lameness.16
This clinical observation is valid if solar toe pain can be eliminated with hoof testers
as a cause of lameness.
The effect of time on interpretation of analgesia of the DIP joint or navicular
bursa
Some clinicians have assumed that improvement in lameness observed within 10
minutes after injecting the DIP joint with local anaesthetic solution indicates that
lameness is caused by pain in the DIP joint alone and that improvement observed
more than 10 minutes after injection is caused by diffusion of local anaesthetic
solution into the navicular bursa or around the nerves providing sensory innervation
to the navicular bone and its associated structures.14,17 This assumption appears to
be invalid because a positive response to intra-articular analgesia of the DIP joint
has been observed to occur within 5 to 8 minutes of injection in a majority of horses
with navicular disease or experimentally-induced navicular bursal pain.9,16
Intra- articular and perineural analgesia of the proximal interphalangeal (PIP)
(pastern) joint
Approaches to the PIP joint have been reviewed18 and include dorsal, dorsolateral,
palmaroproximal, and palmarolateral approaches. Synovial fluid is frequently
observed with the palmaroproximal and palmarolateral approaches but is observed
rarely using the other approaches. Three of these approaches for arthrocentesis of
the PIP joint were evaluated for accuracy by Poore, et al.19 who found that students
inexperienced in arthrocentesis of the PIP joint were usually unsuccessful when
performing these approaches.
A positive response to intra-articular analgesia of the pastern joint localises pain
causing lameness to that joint. Some horse lame because of in the pastern joint,
however, do not respond positively to intra-articular analgesia of the pastern joint
when joint disease involves subchondral bone.20 Because subchondral bone is
innervated by nerves that enter the bone marrow via the nutrient foramen,
anaesthesia of nerves proximal to branches that enter the nutrient foramen may be
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
46