necessary to resolve subchondral bone pain and lameness. Because the pastern
joint is innervated by branches of the palmar digital nerves and their dorsal
branches, 4 an ASNB or BSNB nerve block resolves lameness caused by pain in the
pastern joint. Perineural anaesthesia of the palmar digital nerves and their dorsal
branches at this location should also anaesthetize these nerves proximal to the origin
of the branches that enter the nutrient foramen of the proximal phalanx and resolve
lameness caused by subchondral bone pain. Marked improvement in lameness of a
horse with disease of the proximal interphalangeal joint was observed when
mepivacaine was infused through holes drilled into the medullary cavity of both the
first and second phalanges of the affected digit (Caldwell and Schumacher,
unpublished dataa).
Intra-articular analgesia of the metacarpo/metatarso phalangeal (MC/MT-P)
(fetlock) joint
Several techniques are described for intra-articular analgesia of the MC/MT-P joint.
The authors prefer the technique described by Misheff and Stover21 during which the
limb is positioned in partial flexion by holding the foot with one hand, while the needle
is introduced through the collateral sesamoidean ligament into the space between
the articular surface of the lateral sesamoid bone and the palmar aspect of the lateral
metacarpal condyle. A volume of 7-10 mL mepivacaine is administered.
Although a positive re sponse to intra-articular analgesia of the MC/MT-P joint
localises disease to that joint in most horses, not all lameness associated with an
injury of the fetlock joint resolves with intra-articular analgesia, and not all horses
with lameness that improves with intra-articular analgesia of this joint have disease
of this joint. Whereas lameness caused by intra-articular fragmentation, synovitis,
capsulitis, and osteoarthritis improves or resolves after intra-articular analgesia,
lameness caused by injury of the subchondral bone or peri-articular ligaments does
not. Lameness caused by desmitis of the proximal portion of the straight or an
oblique distal sesamoidean ligament can improve after intra-articular analgesia of the
MC/MT-P joint.22
Analgesia of the digital flexor tendon sheath (DFTS)
Synoviocentesis of the DFTS can be performed by placing a 20- to 22-gauge needle
into one of the sheath’s several pouches. Access to these pouches is not difficult
when the sheath is distended with synovial fluid but is often difficult when it is not. A
palmar axial sesamoidian approach through the palmar/plantar annular ligament of
the MC/MT-P joint is consistently reliable for accurate synoviocentesis of the DFTS.23
Using this approach, the MC/MT-P joint is flexed to a dorsal angle of 225o, the
needle is placed through the skin at the level of the midbody of the lateral proximal
sesamoid bone, and then through the palmar annular ligament, 3 mm axial to the
palpable palmar border of the lateral proximal sesamoid bone, immediately palmar to
the palmar digital neurovascular bundle. The needle is inserted in a transverse plane
and advanced at an angle of 45 o to the sagittal plane, aiming toward the central
intersesamoidean region, to a depth of 1.5 to 2.0 cm.
A basilar sesamoidian approach to the DFTS24 is likely to result in retrieval of
synovial fluid to verify accuracy. To perform the basilar sesamoidian approach the
fetlock joint is held in a slightly flexed position and the needle is inserted distal to the
lateral proximal sesamoid bone into a palpable depression created by the base of
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
47