Page 704 - Adams and Stashak's Lameness in Horses, 7th Edition

670 Chapter 5

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A B
Figure 5.70. The outcome of horses that undergo natural ankylosis of the hocks is variable. The tarsus on the left (A) has nearly fused
naturally and the horse is sound. The one on the right (B) is attempting to fuse secondary to an infectious process and remains consistently lame.

radiographically or fluoroscopically controlled surgical time compared with other methods. 67,68,130 Surgeons per-
drilling of the articular cartilage is essential to maintain forming this technique suggest that horses with radio-
the drill within the joint space to allow the removal of graphic changes such as severe periarticular osteophyte
the maximum amount of articular cartilage. formation or excessive mineralization of the joint cap-
The use of internal fixation in horses with DT disease sule require a modification of the laser procedure to
has not been shown to improve the success rate of facilitate placement of the laser fiber into the joint. These
arthrodesis beyond drilling alone. If the PIT joint is changes may signify a less favorable prognosis after
involved, the prognosis is less favorable, but it too surgery.
should be drilled, because this offers the best chance of In one study that compared three methods of laser
a complete recovery. Other techniques that have been arthrodesis, the energy applied to the DT joints did not
utilized in addition to drilling include intramedullary result in generalized articular cartilage destruction when
decompression or fenestration of the DT bones. This has evaluated with MRI and histology. Full‐thickness
151
been proposed to provide rapid pain relief in some thermal destruction of the articular cartilage extended
horses, but this has not been proven. Complications of only a few millimeters from the insertion site of the laser
IA drilling include fracture of the CT or T3 bone(s), across the joint. It was also speculated that the laser may
development of OA in the PIT joint, and continued cause less postoperative pain due to thermal damage to
lameness despite apparent bone bridging of the DT nerve endings in the subchondral bone, synovium, and
joints. The latter may be due to micromotion between joint capsule, resulting in decreased pain perception in
the tarsal bones and splint bones or bone on bone con- horses after treatment. 151
tact secondary to cartilage destruction from the treat-
ment technique used.
Chemical‐Induced Arthrodesis: Ethyl Alcohol
Ethyl alcohol is a colorless liquid that has been
Laser Arthrodesis reported to provide clinical success in facilitated anky-
Laser‐facilitated arthrodesis is another technique to loses of the DT joints. Ethyl alcohol is thought to affect
promote fusion of the DT joints. This technique has chondrocytes (neurolysis and tissue destruction at the
been most commonly been performed using the neo- drug–tissue interface) in a manner similar to monoio-
dymium–yttrium aluminum garnet (Nd:YAG) or 980‐nm doacetate (MIA) but without the severe postinjection
diode laser (Figure 5.72). Laser arthrodesis is thought to pain. MIA has been evaluated and utilized in the past to
be effective because it destroys the articular cartilage by chemically induce arthrodesis but has fallen out of favor
superheating and vaporizing synovial fluid. It has been due to the severity of postinjection pain and the devel-
suggested that the increased temperatures that develop opment of severe long‐term complications (PIT and TC
within the joint result in chondrocyte death as well as a OA). 16,18,37,126 Like MIA, ethyl alcohol can be easily
collagen shift in the intertarsal ligaments and joint cap- injected into the joints, and because of its neurolytic and
sule. Reports on horses with laser‐facilitated arthrodesis nonselective protein destructive properties, it has the
suggest improvement in the successful outcome with potential to block sensory innervation to the joint
minimal postoperative pain and decreased convalescent while causing necrosis of chondrocytes and hastening